Android中measure过程、WRAP_CONTENT详解以及xml布局文件解析流程浅析(下)
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Android中measure过程、WRAP_CONTENT详解以及xml布局文件解析流程浅析(下)
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public?class?View?implements?...?{?? ?????...?? ?????public?static?class?MeasureSpec?{?? ????????private?static?final?int?MODE_SHIFT?=?30;?//移位位數(shù)為30?? ????????//int類型占32位，向右移位30位，該屬性表示掩碼值，用來與size和mode進(jìn)行"&"運(yùn)算，獲取對(duì)應(yīng)值。?? ????????private?static?final?int?MODE_MASK??=?0x3?<<?MODE_SHIFT;?? ?? ????????//向右移位30位，其值為00?+?(30位0)??,?即?0x0000(16進(jìn)制表示)?? ????????public?static?final?int?UNSPECIFIED?=?0?<<?MODE_SHIFT;?? ????????//向右移位30位，其值為01?+?(30位0)??,?即0x1000(16進(jìn)制表示)?? ????????public?static?final?int?EXACTLY?????=?1?<<?MODE_SHIFT;?? ????????//向右移位30位，其值為02?+?(30位0)??,?即0x2000(16進(jìn)制表示)?? ????????public?static?final?int?AT_MOST?????=?2?<<?MODE_SHIFT;?? ?? ????????//創(chuàng)建一個(gè)整形值，其高兩位代表mode類型，其余30位代表長(zhǎng)或?qū)挼膶?shí)際值。可以是WRAP_CONTENT、MATCH_PARENT或具體大小exactly?size?? ????????public?static?int?makeMeasureSpec(int?size,?int?mode)?{?? ????????????return?size?+?mode;?? ????????}?? ????????//獲取模式??，與運(yùn)算?? ????????public?static?int?getMode(int?measureSpec)?{?? ????????????return?(measureSpec?&?MODE_MASK);?? ????????}?? ????????//獲取長(zhǎng)或?qū)挼膶?shí)際值?，與運(yùn)算?? ????????public?static?int?getSize(int?measureSpec)?{?? ????????????return?(measureSpec?&?~MODE_MASK);?? ????????}?? ?? ????}?? ????...?? }??
? ?? MeasureSpec類的處理思路是：路徑：\frameworks\base\core\java\android\view\ViewRoot.java?? public?final?class?ViewRoot?extends?Handler?implements?ViewParent,View.AttachInfo.Callbacks?{?? ????...?? ????//mView對(duì)象指添加至窗口的root?View?，對(duì)Activity窗口而言，則是DecorView對(duì)象。?? ????View?mView;?????? ?????? ????//開始View繪制流程?? ????private?void?performTraversals(){?? ????????...?? ????????//這兩個(gè)值我們?cè)诤竺嬗懻摃r(shí)，在回過頭來看看是怎么賦值的。現(xiàn)在只需要記住其值MeasureSpec.makeMeasureSpec()構(gòu)建的。?? ????????int?childWidthMeasureSpec;?//其值由MeasureSpec類構(gòu)建?,?makeMeasureSpec?? ????????int?childHeightMeasureSpec;//其值由MeasureSpec類構(gòu)建?,?makeMeasureSpec?? ?????????? ?? ????????//?Ask?host?how?big?it?wants?to?be?? ????????host.measure(childWidthMeasureSpec,?childHeightMeasureSpec);?? ????????...?? ????}?? ????...?? }??
這兒，我并沒有說出childWidthMeasureSpec和childHeightMeasureSpec類的來由(為了避免額外地開銷，等到 第三部分時(shí)我們?cè)趤砉タ怂?#xff0c;現(xiàn)在只需要記住其值MeasureSpec.makeMeasureSpec()構(gòu)建的。
public?class?View?implements?...?{?? ????...?? ????/**? ?????*?This?is?called?to?find?out?how?big?a?view?should?be.?The?parent? ?????*?supplies?constraint?information?in?the?width?and?height?parameters.? ?????*? ?????*?@param?widthMeasureSpec?Horizontal?space?requirements?as?imposed?by?the? ?????*????????parent? ?????*?@param?heightMeasureSpec?Vertical?space?requirements?as?imposed?by?the? ?????*????????parent? ?????*?@see?#onMeasure(int,?int)? ?????*/?? ????public?final?void?measure(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ????????//判斷是否為強(qiáng)制布局，即帶有“FORCE_LAYOUT”標(biāo)記?以及?widthMeasureSpec或heightMeasureSpec發(fā)生了改變?? ????????if?((mPrivateFlags?&?FORCE_LAYOUT)?==?FORCE_LAYOUT?||?? ????????????????widthMeasureSpec?!=?mOldWidthMeasureSpec?||?? ????????????????heightMeasureSpec?!=?mOldHeightMeasureSpec)?{?? ?? ????????????//?first?clears?the?measured?dimension?flag?? ????????????//清除MEASURED_DIMENSION_SET標(biāo)記???，該標(biāo)記會(huì)在onMeasure()方法后被設(shè)置?? ????????????mPrivateFlags?&=?~MEASURED_DIMENSION_SET;??? ?? ????????????//?measure?ourselves,?this?should?set?the?measured?dimension?flag?back?? ????????????//?1、?測(cè)量該View本身的大小?；?2?、?設(shè)置MEASURED_DIMENSION_SET標(biāo)記，否則接寫來會(huì)報(bào)異常。?? ????????????onMeasure(widthMeasureSpec,?heightMeasureSpec);?? ?? ????????????//?flag?not?set,?setMeasuredDimension()?was?not?invoked,?we?raise?? ????????????//?an?exception?to?warn?the?developer?? ????????????if?((mPrivateFlags?&?MEASURED_DIMENSION_SET)?!=?MEASURED_DIMENSION_SET)?{?? ????????????????throw?new?IllegalStateException("onMeasure()?did?not?set?the"?? ????????????????????????+?"?measured?dimension?by?calling"?+?"?setMeasuredDimension()");?? ????????????}?? ?? ????????????mPrivateFlags?|=?LAYOUT_REQUIRED;??//下一步是layout了，添加LAYOUT_REQUIRED標(biāo)記?? ????????}?? ?? ????????mOldWidthMeasureSpec?=?widthMeasureSpec;???//保存值?? ????????mOldHeightMeasureSpec?=?heightMeasureSpec;?//保存值?? ????}?? ????...?? }??
/**? ???*?Measure?the?view?and?its?content?to?determine?the?measured?width?and?the? ???*?measured?height.?This?method?is?invoked?by?{@link?#measure(int,?int)}?and? ???*?should?be?overriden?by?subclasses?to?provide?accurate?and?efficient? ???*?measurement?of?their?contents.? ???*?? ???*?@param?widthMeasureSpec?horizontal?space?requirements?as?imposed?by?the?parent.? ???*?????????????????????????The?requirements?are?encoded?with? ???*?@param?heightMeasureSpec?vertical?space?requirements?as?imposed?by?the?parent.? ???*?????????????????????????The?requirements?are?encoded?with? ???*/?? ??//設(shè)置該View本身地大小?? ??protected?void?onMeasure(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ??????setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(),?widthMeasureSpec),?? ??????????????getDefaultSize(getSuggestedMinimumHeight(),?heightMeasureSpec));?? ??}?? ???? ??/**? ???*?Utility?to?return?a?default?size.?Uses?the?supplied?size?if?the? ???*?MeasureSpec?imposed?no?contraints.?Will?get?larger?if?allowed? ???*?by?the?MeasureSpec.? ???*? ???*?@param?size?Default?size?for?this?view? ???*?@param?measureSpec?Constraints?imposed?by?the?parent? ???*?@return?The?size?this?view?should?be.? ???*/?? ??//@param?size參數(shù)一般表示設(shè)置了android:minHeight屬性或者該View背景圖片的大小值?? ??public?static?int?getDefaultSize(int?size,?int?measureSpec)?{?? ??????int?result?=?size;???? ??????int?specMode?=?MeasureSpec.getMode(measureSpec);?? ??????int?specSize?=??MeasureSpec.getSize(measureSpec);?? ?? ??????//根據(jù)不同的mode值，取得寬和高的實(shí)際值。?? ??????switch?(specMode)?{?? ??????case?MeasureSpec.UNSPECIFIED:??//表示該View的大小父視圖未定，設(shè)置為默認(rèn)值?? ??????????result?=?size;?? ??????????break;?? ??????case?MeasureSpec.AT_MOST:??????//表示該View的大小由父視圖指定了?? ??????case?MeasureSpec.EXACTLY:?? ??????????result?=?specSize;?? ??????????break;?? ??????}?? ??????return?result;?? ??}?? ??//獲得設(shè)置了android:minHeight屬性或者該View背景圖片的大小值，?最為該View的參考值?? ??protected?int?getSuggestedMinimumWidth()?{?? ??????int?suggestedMinWidth?=?mMinWidth;??//??android:minHeight?? ?? ??????if?(mBGDrawable?!=?null)?{?//?背景圖片對(duì)應(yīng)地Width。?? ??????????final?int?bgMinWidth?=?mBGDrawable.getMinimumWidth();?? ??????????if?(suggestedMinWidth?<?bgMinWidth)?{?? ??????????????suggestedMinWidth?=?bgMinWidth;?? ??????????}?? ??????}?? ?? ??????return?suggestedMinWidth;?? ??}?? ??//設(shè)置View在measure過程中寬和高?? ??protected?final?void?setMeasuredDimension(int?measuredWidth,?int?measuredHeight)?{?? ??????mMeasuredWidth?=?measuredWidth;?? ??????mMeasuredHeight?=?measuredHeight;?? ?? ??????mPrivateFlags?|=?MEASURED_DIMENSION_SET;??//設(shè)置了MEASURED_DIMENSION_SET標(biāo)記?? ??}??
//某個(gè)ViewGroup類型的視圖?? protected?void?onMeasure(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ??//必須調(diào)用super.ononMeasure()或者直接調(diào)用setMeasuredDimension()方法設(shè)置該View大小，否則會(huì)報(bào)異常。?? ??super.onMeasure(widthMeasureSpec?,?heightMeasureSpec)?? ?????//setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(),?widthMeasureSpec),?? ?????//????????getDefaultSize(getSuggestedMinimumHeight(),?heightMeasureSpec));?? ??????? ??//遍歷每個(gè)子View?? ??for(int?i?=?0?;?i?<?getChildCount()?;?i++){?? ????View?child?=?getChildAt(i);?? ????//調(diào)用子View的onMeasure，設(shè)置他們的大小。childWidthMeasureSpec?，?childHeightMeasureSpec???? ????child.onMeasure(childWidthMeasureSpec,?childHeightMeasureSpec);?? ??}?? }??
/**? ?*?Ask?all?of?the?children?of?this?view?to?measure?themselves,?taking?into? ?*?account?both?the?MeasureSpec?requirements?for?this?view?and?its?padding.? ?*?We?skip?children?that?are?in?the?GONE?state?The?heavy?lifting?is?done?in? ?*?getChildMeasureSpec.? ?*/?? //widthMeasureSpec?和??heightMeasureSpec?表示該父View的布局要求?? //遍歷每個(gè)子View，然后調(diào)用measureChild()方法去實(shí)現(xiàn)每個(gè)子View大小?? protected?void?measureChildren(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ????final?int?size?=?mChildrenCount;?? ????final?View[]?children?=?mChildren;?? ????for?(int?i?=?0;?i?<?size;?++i)?{?? ????????final?View?child?=?children[i];?? ????????if?((child.mViewFlags?&?VISIBILITY_MASK)?!=?GONE)?{?//?不處于?“GONE”?狀態(tài)?? ????????????measureChild(child,?widthMeasureSpec,?heightMeasureSpec);?? ????????}?? ????}?? }?? ????? /**? ?*?Ask?one?of?the?children?of?this?view?to?measure?itself,?taking?into? ?*?account?both?the?MeasureSpec?requirements?for?this?view?and?its?padding.? ?*?The?heavy?lifting?is?done?in?getChildMeasureSpec.? ?*? ?*?@param?child?The?child?to?measure? ?*?@param?parentWidthMeasureSpec?The?width?requirements?for?this?view? ?*?@param?parentHeightMeasureSpec?The?height?requirements?for?this?view? ?*/?? //測(cè)量每個(gè)子View高寬時(shí)，清楚了該View本身的邊距大小，即android:padding屬性?或android:paddingLeft等屬性標(biāo)記?? protected?void?measureChild(View?child,?int?parentWidthMeasureSpec,?? ????????int?parentHeightMeasureSpec)?{?? ????final?LayoutParams?lp?=?child.getLayoutParams();?//?LayoutParams屬性?? ????//設(shè)置子View的childWidthMeasureSpec屬性，去除了該父View的邊距值??mPaddingLeft?+?mPaddingRight?? ????final?int?childWidthMeasureSpec?=?getChildMeasureSpec(parentWidthMeasureSpec,?? ????????????mPaddingLeft?+?mPaddingRight,?lp.width);?? ????//設(shè)置子View的childHeightMeasureSpec屬性，去除了該父View的邊距值??mPaddingTop?+?mPaddingBottom?? ????final?int?childHeightMeasureSpec?=?getChildMeasureSpec(parentHeightMeasureSpec,?? ????????????mPaddingTop?+?mPaddingBottom,?lp.height);?? ?? ????child.measure(childWidthMeasureSpec,?childHeightMeasureSpec);?? }??
??
/**? ?*?Does?the?hard?part?of?measureChildren:?figuring?out?the?MeasureSpec?to? ?*?pass?to?a?particular?child.?This?method?figures?out?the?right?MeasureSpec? ?*?for?one?dimension?(height?or?width)?of?one?child?view.? ?*? ?*?The?goal?is?to?combine?information?from?our?MeasureSpec?with?the? ?*?LayoutParams?of?the?child?to?get?the?best?possible?results.? ?*/?? //?spec參數(shù)????????????????????????????????????表示該父View本身所占的widthMeasureSpec?或??heightMeasureSpec值?? //?padding參數(shù)??????????????????????????表示該父View的邊距大小，見于android:padding屬性?或android:paddingLeft等屬性標(biāo)記?? //?childDimension參數(shù)??表示該子View內(nèi)部LayoutParams屬性的值，可以是wrap_content、match_parent、一個(gè)精確指(an?exactly?size),?? //???????????例如：由android:width指定等。?? public?static?int?getChildMeasureSpec(int?spec,?int?padding,?int?childDimension)?{?? ????int?specMode?=?MeasureSpec.getMode(spec);??//獲得父View的mode?? ????int?specSize?=?MeasureSpec.getSize(spec);??//獲得父View的實(shí)際值?? ?? ????int?size?=?Math.max(0,?specSize?-?padding);?//父View為子View設(shè)定的大小，減去邊距值，?? ?? ????int?resultSize?=?0;????//子View對(duì)應(yīng)地?size?實(shí)際值?，由下面的邏輯條件賦值?? ????int?resultMode?=?0;????//子View對(duì)應(yīng)地?mode?值?，?由下面的邏輯條件賦值?? ?? ????switch?(specMode)?{?? ????//?Parent?has?imposed?an?exact?size?on?us?? ????//1、父View是EXACTLY的?！?? ????case?MeasureSpec.EXACTLY:??? ????????//1.1、子View的width或height是個(gè)精確值?(an?exactly?size)?? ????????if?(childDimension?>=?0)?{???????????? ????????????resultSize?=?childDimension;?????????//size為精確值?? ????????????resultMode?=?MeasureSpec.EXACTLY;????//mode為?EXACTLY?。?? ????????}??? ????????//1.2、子View的width或height為?MATCH_PARENT/FILL_PARENT??? ????????else?if?(childDimension?==?LayoutParams.MATCH_PARENT)?{?? ????????????//?Child?wants?to?be?our?size.?So?be?it.?? ????????????resultSize?=?size;???????????????????//size為父視圖大小?? ????????????resultMode?=?MeasureSpec.EXACTLY;????//mode為?EXACTLY?。?? ????????}??? ????????//1.3、子View的width或height為?WRAP_CONTENT?? ????????else?if?(childDimension?==?LayoutParams.WRAP_CONTENT)?{?? ????????????//?Child?wants?to?determine?its?own?size.?It?can't?be?? ????????????//?bigger?than?us.?? ????????????resultSize?=?size;???????????????????//size為父視圖大小?? ????????????resultMode?=?MeasureSpec.AT_MOST;????//mode為AT_MOST?。?? ????????}?? ????????break;?? ?? ????//?Parent?has?imposed?a?maximum?size?on?us?? ????//2、父View是AT_MOST的?！?????? ????case?MeasureSpec.AT_MOST:?? ????????//2.1、子View的width或height是個(gè)精確值?(an?exactly?size)?? ????????if?(childDimension?>=?0)?{?? ????????????//?Child?wants?a?specific?size...?so?be?it?? ????????????resultSize?=?childDimension;????????//size為精確值?? ????????????resultMode?=?MeasureSpec.EXACTLY;???//mode為?EXACTLY?。?? ????????}?? ????????//2.2、子View的width或height為?MATCH_PARENT/FILL_PARENT?? ????????else?if?(childDimension?==?LayoutParams.MATCH_PARENT)?{?? ????????????//?Child?wants?to?be?our?size,?but?our?size?is?not?fixed.?? ????????????//?Constrain?child?to?not?be?bigger?than?us.?? ????????????resultSize?=?size;??????????????????//size為父視圖大小?? ????????????resultMode?=?MeasureSpec.AT_MOST;???//mode為AT_MOST?? ????????}?? ????????//2.3、子View的width或height為?WRAP_CONTENT?? ????????else?if?(childDimension?==?LayoutParams.WRAP_CONTENT)?{?? ????????????//?Child?wants?to?determine?its?own?size.?It?can't?be?? ????????????//?bigger?than?us.?? ????????????resultSize?=?size;??????????????????//size為父視圖大小?? ????????????resultMode?=?MeasureSpec.AT_MOST;???//mode為AT_MOST?? ????????}?? ????????break;?? ?? ????//?Parent?asked?to?see?how?big?we?want?to?be?? ????//3、父View是UNSPECIFIED的?！?? ????case?MeasureSpec.UNSPECIFIED:?? ????????//3.1、子View的width或height是個(gè)精確值?(an?exactly?size)?? ????????if?(childDimension?>=?0)?{?? ????????????//?Child?wants?a?specific?size...?let?him?have?it?? ????????????resultSize?=?childDimension;????????//size為精確值?? ????????????resultMode?=?MeasureSpec.EXACTLY;???//mode為?EXACTLY?? ????????}?? ????????//3.2、子View的width或height為?MATCH_PARENT/FILL_PARENT?? ????????else?if?(childDimension?==?LayoutParams.MATCH_PARENT)?{?? ????????????//?Child?wants?to?be?our?size...?find?out?how?big?it?should?? ????????????//?be?? ????????????resultSize?=?0;????????????????????????//size為0！?,其值未定?? ????????????resultMode?=?MeasureSpec.UNSPECIFIED;??//mode為?UNSPECIFIED?? ????????}??? ????????//3.3、子View的width或height為?WRAP_CONTENT?? ????????else?if?(childDimension?==?LayoutParams.WRAP_CONTENT)?{?? ????????????//?Child?wants?to?determine?its?own?size....?find?out?how?? ????????????//?big?it?should?be?? ????????????resultSize?=?0;????????????????????????//size為0!?，其值未定?? ????????????resultMode?=?MeasureSpec.UNSPECIFIED;??//mode為?UNSPECIFIED?? ????????}?? ????????break;?? ????}?? ????//根據(jù)上面邏輯條件獲取的mode和size構(gòu)建MeasureSpec對(duì)象。?? ????return?MeasureSpec.makeMeasureSpec(resultSize,?resultMode);?? }??
//設(shè)置View在measure過程中寬和高?? protected?final?void?setMeasuredDimension(int?measuredWidth,?int?measuredHeight)?{?? ????mMeasuredWidth?=?measuredWidth;?? ????mMeasuredHeight?=?measuredHeight;?? ?? ????mPrivateFlags?|=?MEASURED_DIMENSION_SET;??//設(shè)置了MEASURED_DIMENSION_SET標(biāo)記?? }??
<?xml?version="1.0"?encoding="utf-8"?>?? <LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android"?? ????android:id="@+id/llayout"?? ???????android:orientation="vertical"??? ????android:layout_width="match_parent"?? ???????android:layout_height="match_parent">?? ?????? ?????? ????<TextView?android:id="@+id/tv"??? ????????android:layout_width="match_parent"?? ????????android:layout_height="wrap_content"?? ????????android:text="@string/hello"?/>?? ?? </LinearLayout>?????
?public?class?LinearLayout?extends?ViewGroup?{?? ...?? @Override??//onMeasure方法。?? protected?void?onMeasure(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ????//判斷是垂直方向還是水平方向，這兒我們假設(shè)是VERTICAL垂直方向，?? ????if?(mOrientation?==?VERTICAL)?{?? ????????measureVertical(widthMeasureSpec,?heightMeasureSpec);?? ????}?else?{?? ????????measureHorizontal(widthMeasureSpec,?heightMeasureSpec);?? ????}?? }?? //垂直方向布局?? ???void?measureVertical(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? ???????mTotalLength?=?0;?????????//該LinearLayout測(cè)量子View時(shí)的總高度。?? ????float?totalWeight?=?0;????//所有子View的權(quán)重和?,?android:layout_weight?? ????int?maxWidth?=?0;?????????//保存子View中最大width值?? ???????...?? ???????final?int?count?=?getVirtualChildCount();??//子View的個(gè)數(shù)?? ????????? ???????final?int?widthMode?=?MeasureSpec.getMode(widthMeasureSpec);?? ???????final?int?heightMode?=?MeasureSpec.getMode(heightMeasureSpec);?? ??????????...?? ???????//?See?how?tall?everyone?is.?Also?remember?max?width.?? ???????for?(int?i?=?0;?i?<?count;?++i)?{?? ???????????final?View?child?=?getVirtualChildAt(i);?? ??????????????...?? ???????????LinearLayout.LayoutParams?lp?=?(LinearLayout.LayoutParams)?child.getLayoutParams();?? ?? ???????????totalWeight?+=?lp.weight;???? ???????????//滿足該條件地View會(huì)在該LinearLayout有剩余高度時(shí)，才真正調(diào)用measure()?? ???????????if?(heightMode?==?MeasureSpec.EXACTLY?&&?lp.height?==?0?&&?lp.weight?>?0)?{?? ???????????????...?? ???????????}?else?{?? ???????????????int?oldHeight?=?Integer.MIN_VALUE;?? ???????????????//如果View的hight值為0，并且設(shè)置了android:layout_weight屬性，重新糾正其height值為WRAP_CONTENT?? ???????????????if?(lp.height?==?0?&&?lp.weight?>?0)?{?? ???????????????????oldHeight?=?0;?? ???????????????????lp.height?=?LayoutParams.WRAP_CONTENT;?? ???????????????}?? ???????????????//?Determine?how?big?this?child?would?like?to?be.?If?this?or?? ???????????????//?previous?children?have?given?a?weight,?then?we?allow?it?to?? ???????????????//?use?all?available?space?(and?we?will?shrink?things?later?? ???????????????//?if?needed).?? ???????????????//對(duì)每個(gè)子View調(diào)用measure()方法?? ???????????????measureChildBeforeLayout(?? ??????????????????????child,?i,?widthMeasureSpec,?0,?heightMeasureSpec,?? ??????????????????????totalWeight?==?0???mTotalLength?:?0);?? ????????????????? ???????????????//這三行代碼做了如下兩件事情：?? ???????????????//1、獲得該View的measuredHeight值，每個(gè)View都會(huì)根據(jù)他們地屬性正確設(shè)置值??>?0?;?? ???????????????//2、更新mTotalLength值：取當(dāng)前高度mTotalLength值與mTotalLength?+?childHeight?的最大值?? ???????????????//?于是對(duì)于android:layout_height="wrap_height"屬性地LinearLayout控件也就知道了它的確切高度值了。?? ???????????????final?int?childHeight?=?child.getMeasuredHeight();?? ???????????????final?int?totalLength?=?mTotalLength;?? ???????????????mTotalLength?=?Math.max(totalLength,?totalLength?+?childHeight?+?lp.topMargin?+?? ??????????????????????lp.bottomMargin?+?getNextLocationOffset(child));?? ???????????????...?? ???????????}?? ???????????final?int?margin?=?lp.leftMargin?+?lp.rightMargin;?? ???????????final?int?measuredWidth?=?child.getMeasuredWidth()?+?margin;?? ???????????maxWidth?=?Math.max(maxWidth,?measuredWidth);?? ???????????...?? ???????}?? ??????????//后續(xù)還有很多處理，包括繼續(xù)measure()某些符合條件地子View?? ???????...?? ???}?? ???void?measureChildBeforeLayout(View?child,?int?childIndex,?? ???????????int?widthMeasureSpec,?int?totalWidth,?int?heightMeasureSpec,?? ???????????int?totalHeight)?{?? ????//調(diào)用measureChildWithMargins()方法去設(shè)置子View大小?? ???????measureChildWithMargins(child,?widthMeasureSpec,?totalWidth,?? ???????????????heightMeasureSpec,?totalHeight);?? ???}?? ...??
? ? ? ? ??/**? ?*?Ask?one?of?the?children?of?this?view?to?measure?itself,?taking?into? ?*?account?both?the?MeasureSpec?requirements?for?this?view?and?its?padding? ?*?and?margins.?The?child?must?have?MarginLayoutParams?The?heavy?lifting?is? ?*?done?in?getChildMeasureSpec.? ?*/?? //基本流程同于measureChild()方法，但添加了對(duì)子View?Margin的處理，即：android:margin屬性或者android:marginLeft等屬性的處理?? //widthUsed參數(shù)??表示該父View已經(jīng)使用的寬度?? //heightUsed參數(shù)??表示該父View已經(jīng)使用的高度?? protected?void?measureChildWithMargins(View?child,?? ????????int?parentWidthMeasureSpec,?int?widthUsed,?? ????????int?parentHeightMeasureSpec,?int?heightUsed)?{?? ????final?MarginLayoutParams?lp?=?(MarginLayoutParams)?child.getLayoutParams();?? ?? ????//獲得子View的childWidthMeasureSpec和childHeightMeasureSpec值?? ????final?int?childWidthMeasureSpec?=?getChildMeasureSpec(parentWidthMeasureSpec,?? ????????????mPaddingLeft?+?mPaddingRight?+?lp.leftMargin?+?lp.rightMargin?? ????????????????????+?widthUsed,?lp.width);?? ????final?int?childHeightMeasureSpec?=?getChildMeasureSpec(parentHeightMeasureSpec,?? ????????????mPaddingTop?+?mPaddingBottom?+?lp.topMargin?+?lp.bottomMargin?? ????????????????????+?heightUsed,?lp.height);?? ?? ????child.measure(childWidthMeasureSpec,?childHeightMeasureSpec);?? }??
//自定義View????? public?Class?MyView?extends?View?{?? ?????? ?????//針對(duì)不同地mode值，設(shè)置本View地大小?? ?????protected?void?onMeasure(int?widthMeasureSpec,?int?heightMeasureSpec){?? ?????????//獲得父View傳遞給我們地測(cè)量需求?? ?????????int?widthMode?=?MeasureSpec.getMode(widthMeasureSpec);?? ?????????int?heightMode?=?MeasureSpec.getMode(heightMeasureSpec);?? ??????????? ?????????int?width?=?0?;?? ?????????int?height?=?0?;?? ?????????//對(duì)UNSPECIFIED?則拋出異常?? ?????????if(widthMode?==?MeasureSpec.UNSPECIFIED?||?heightMode?==?MeasureSpec.UNSPECIFIED)?? ?????????????throw?new?RuntimeException("widthMode?or?heightMode?cannot?be?UNSPECIFIED");?? ?????????? ?????????//精確指定?? ?????????if(widthMode?==?MeasureSpec.EXACTLY){?? ?????????????width?=?100?;?? ?????????}?? ?????????//模糊指定?? ?????????else?if(widthMode?==?MeasureSpec.AT_MOST?)?? ?????????????width?=?50?;??? ??????????? ??????????//精確指定?? ?????????if(heightMode?==?MeasureSpec.EXACTLY){?? ?????????????height?=?100?;?? ?????????}?? ?????????//模糊指定?? ?????????else?if(heightMode?==?MeasureSpec.AT_MOST?)?? ?????????????height?=?50?;?? ??????????? ?????????setMeasuredDimension(width?,?height)?;?? ?????}?? }??
public?class?LinearLayout?extends?ViewGroup?{?? ????...?? ????@Override??//layout?過程?? ????protected?void?onLayout(boolean?changed,?int?l,?int?t,?int?r,?int?b)?{?? ????????//假定是垂直方向布局?? ????????if?(mOrientation?==?VERTICAL)?{?? ????????????layoutVertical();?? ????????}?else?{?? ????????????layoutHorizontal();?? ????????}?? ????}?? ????//對(duì)每個(gè)子View調(diào)用layout過程?? ????void?layoutVertical()?{?? ????????...?? ????????final?int?count?=?getVirtualChildCount();?? ????????...?? ????????for?(int?i?=?0;?i?<?count;?i++)?{?? ????????????final?View?child?=?getVirtualChildAt(i);?? ????????????if?(child?==?null)?{??//一般為非null?? ????????????????childTop?+=?measureNullChild(i);?? ????????????}?else?if?(child.getVisibility()?!=?GONE)?{?? ????????????????//獲得子View測(cè)量時(shí)的實(shí)際寬高值，?? ????????????????final?int?childWidth?=?child.getMeasuredWidth();?? ????????????????final?int?childHeight?=?child.getMeasuredHeight();?? ?????????????????? ????????????????...?? ????????????????//??封裝了child.layout()方法，見如下?? ????????????????setChildFrame(child,?childLeft,?childTop?+?getLocationOffset(child),?? ????????????????????????childWidth,?childHeight);??? ????????????????childTop?+=?childHeight?+?lp.bottomMargin?+?getNextLocationOffset(child);?? ?? ????????????????i?+=?getChildrenSkipCount(child,?i);?? ????????????}?? ????????}?? ????}?? ????//width?=?getMeasuredWidth()?;?height?=?childHeight();?View的大小就是測(cè)量大小?? ????private?void?setChildFrame(View?child,?int?left,?int?top,?int?width,?int?height)?{?? ?????????? ????????child.layout(left,?top,?left?+?width,?top?+?height);?? ????}?? ????...?? }?????
//自定義ViewGroup?，?包含了三個(gè)LinearLayout控件，存放在不同的布局位置?? public?class?MultiViewGroup?extends?ViewGroup?{?? ????private?void?init()?{?? ????????//?初始化3個(gè)?LinearLayout控件?? ????????LinearLayout?oneLL?=?new?LinearLayout(mContext);?? ????????oneLL.setBackgroundColor(Color.RED);?? ????????addView(oneLL);?? ????????...?? ????}?? ????@Override?? ????//?我們知曉每個(gè)子View的layout布局大小，因此我們不需要為每個(gè)子View進(jìn)行measure()操作了。?? //??protected?void?onMeasure(int?widthMeasureSpec,?int?heightMeasureSpec)?{?? //??????setMeasuredDimension(width,?height);?? //??????//?設(shè)置該ViewGroup的大小?? //??????int?width?=?MeasureSpec.getSize(widthMeasureSpec);?? //??????int?height?=?MeasureSpec.getSize(heightMeasureSpec);?? //??????int?childCount?=?getChildCount();?? //??????for?(int?i?=?0;?i?<?childCount;?i++)?{?? //??????????View?child?=?getChildAt(i);?? //??????????//?設(shè)置每個(gè)子視圖的大小?，?即全屏?? //??????????child.measure(MultiScreenActivity.screenWidth,?MultiScreenActivity.scrrenHeight);?? //??????}?? ????}?? ?? ????//?layout過程?? ????@Override?? ????protected?void?onLayout(boolean?changed,?int?l,?int?t,?int?r,?int?b)?{?? ????????//?TODO?Auto-generated?method?stub?? ????????Log.i(TAG,?"---?start?onLayout?--");?? ????????int?startLeft?=?0;?//?每個(gè)子視圖的起始布局坐標(biāo)?? ????????int?startTop?=?10;?//?間距設(shè)置為10px?相當(dāng)于?android：marginTop=?"10px"?? ????????int?childCount?=?getChildCount();?? ????????Log.i(TAG,?"---?onLayout?childCount?is?-->"?+?childCount);?? ????????for?(int?i?=?0;?i?<?childCount;?i++)?{?? ????????????View?child?=?getChildAt(i);?? ????????????child.layout(startLeft,?startTop,??? ????????????????????startLeft?+?MultiScreenActivity.screenWidth,??? ????????????????????startTop?+?MultiScreenActivity.scrrenHeight);?? ????????????startLeft?=?startLeft?+?MultiScreenActivity.screenWidth?;?//校準(zhǔn)每個(gè)子View的起始布局位置?? ????????????//三個(gè)子視圖的在屏幕中的分布如下?[0?,?320]?/?[320,640]?/?[640,960]?? ????????}?? ????}?? }????
? ? ? ? ?老子道德經(jīng)有言：“道生一，一生二，二生三，三生萬物。” ?UI繪制也就是個(gè)遞歸過程。理解其基本架構(gòu)后， ?也就“掌握了一個(gè)中心點(diǎn)”了。在第一節(jié)中，我們沒有說明開始UI繪制時(shí) ，沒有說明mView.measure()參數(shù)地由來， ?參數(shù)也就是我們本節(jié)需要弄懂的“道” --- root View的 widthMeasureSpec和heightMeasureSpec?是如何確定的。
? ?對(duì)于如下布局文件： main.xml [java] view plaincopyprint?<?xml?version="1.0"?encoding="utf-8"?>?? <LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android"?? ????android:orientation="vertical"?? ????android:layout_width="fill_parent"?? ????android:layout_height="fill_parent"?? ????>?? <TextView???? ????android:layout_width="fill_parent"??? ????android:layout_height="wrap_content"??? ????android:text="@string/hello"?? ????/>?? </LinearLayout>?? ??
? ? 當(dāng)使用LayoutInflater類解析成View時(shí) ，LinearLayout對(duì)象的LayoutParams參數(shù)為null 。具體原因請(qǐng)參考上篇博文
? ? 任何一個(gè)View被添加至窗口時(shí)，都需要利用WindowManager類去操作。例如，如下代碼： ? [java] view plaincopyprint?//顯示一個(gè)懸浮窗吧?，?just?so?so??? public?void?showView()?? {?? ????//解析布局文件?? ????LayoutInflater?layoutInflater?=?(LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);?? ????//rootView對(duì)應(yīng)地LayoutParams屬性值為null，將會(huì)在UI繪制時(shí)設(shè)定其值?? ????View?rootView?=?layoutInflater.inflate(R.layout.main,?null);?? ?????? ????WindowManager?windowManager?=?(WindowManager)getSystemService(Context.WINDOW_SERVICE);?? ????//設(shè)置WindowManager.LayoutParams參數(shù)值，作為該窗口的各種屬性?? ????WindowManager.LayoutParams?winparams?=?WindowManager.LayoutParams();?? ?????//?以屏幕左上角為原點(diǎn)，設(shè)置x、y初始值?? ????winparams.x?=?0;?? ????winparams.y?=?0;?? ?? ????//設(shè)置懸浮窗口長(zhǎng)寬數(shù)據(jù)?? ????winparams.width?=?WindowManager.LayoutParams.WRAP_CONTENT;;?? ????winparams.height?=?WindowManager.LayoutParams.WRAP_CONTENT;;?? ??????? ????windowManager.addView(rootView,?winparams);?? }??
[java] view plaincopyprint???
? ? ???關(guān)于WindowManager的使用請(qǐng)看如下博客 ：
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?<<android學(xué)習(xí)---- WindowManager 接口?>>
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? <<在Android中使用WindowManager實(shí)現(xiàn)懸浮窗口>>
? ? ??關(guān)于WindowManager.LayoutParams類說明請(qǐng)看如下博客：?
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? <<?android學(xué)習(xí)---- WindowManager.LayoutParams>>
? ? ? ?下面，我們從獲得WindowManager對(duì)象引用開始，一步步觀察addView()做了一些什么事情。
? ?Step 1 、獲得WindowManager對(duì)象服務(wù) ，具體實(shí)現(xiàn)類在ContextImpl.java內(nèi)中
? ? ? ? ? ?路徑：?/frameworks/base/core/java/android/app/ContextImpl.java ? ? ? ??
[java] view plaincopyprint? @Override?? public?Object?getSystemService(String?name)?{?? ????if?(WINDOW_SERVICE.equals(name))?{?? ????????return?WindowManagerImpl.getDefault();?? ????}?? ????...?? }?? ? ? ? ??WindowManager是個(gè)接口，具體返回對(duì)象則是WindowManagerImpl的單例對(duì)象。
?Step 2 、?獲得WindowManagerImpl的單例對(duì)象，以及部分源碼分析 ? ? ? ? ? ?路徑：?/frameworks/base/core/java/android/view/WindowManagerImpl.java? [java] view plaincopyprint?public?class?WindowManagerImpl?implements?WindowManager{?? ????????? ???public?static?WindowManagerImpl?getDefault()?? ???{?? ???????return?mWindowManager;?? ???}?? ???//以特定Window屬性添加一個(gè)窗口?? ???public?void?addView(View?view,?ViewGroup.LayoutParams?params)?? ???{?? ???????addView(view,?params,?false);?? ???}?? ???//參數(shù)nest表示該窗口是不是一個(gè)字窗口?? ???private?void?addView(View?view,?ViewGroup.LayoutParams?params,?boolean?nest)?? ???{???...?? ???????final?WindowManager.LayoutParams?wparams?=?(WindowManager.LayoutParams)params;?? ????????? ???????ViewRoot?root;?? ???????View?panelParentView?=?null;????//該子窗口對(duì)應(yīng)地父窗口View?? ????????? ???????synchronized?(this)?{?? ???????????? ???????????...//需要對(duì)傳遞過來地參數(shù)進(jìn)行檢測(cè)...?? ????????????? ???????????//對(duì)每個(gè)窗口皆構(gòu)建一個(gè)ViewRoot對(duì)象?? ???????????root?=?new?ViewRoot(view.getContext());?? ???????????root.mAddNesting?=?1;?? ???????????//設(shè)置root?View?的LayoutParams為wparams，即WindowManager.LayoutParams類型?? ???????????view.setLayoutParams(wparams);?? ???????????...//對(duì)參數(shù)檢測(cè)，以及拷貝原有數(shù)組...?? ????????????? ???????????//將窗口對(duì)應(yīng)地view、root、wparams保存在屬性集合中?? ???????????mViews[index]?=?view;?? ???????????mRoots[index]?=?root;?? ???????????mParams[index]?=?wparams;?? ???????}?? ???????//?do?this?last?because?it?fires?off?messages?to?start?doing?things?? ???????//?調(diào)用ViewRoot對(duì)象去通知系統(tǒng)添加一個(gè)窗口?? ???????root.setView(view,?wparams,?panelParentView);?? ???}?? ???...?? ???//這三個(gè)數(shù)組分別保存了一個(gè)窗口對(duì)應(yīng)地屬性?? ???private?View[]?mViews;?????????//root?View對(duì)象?，?View類型?? ???private?ViewRoot[]?mRoots;?????//ViewRoot類型?，?與WMS通信?? ???private?WindowManager.LayoutParams[]?mParams;??//窗口屬性?? ????? ???//WindowManagerImpl實(shí)現(xiàn)了單例模式?? ???private?static?WindowManagerImpl?mWindowManager?=?new?WindowManagerImpl();?? }??
? ? ??WindowManagerImpl類的三個(gè)數(shù)組集合保存了每個(gè)窗口相關(guān)屬性，這樣我們可以通過這些屬性去操作特定的 ?窗口(例如，可以根據(jù)View去更新/銷毀該窗口)。當(dāng)參數(shù)檢查成功時(shí)，構(gòu)建一個(gè)ViewRoot對(duì)象，并且設(shè)置設(shè)置root ?View 的LayoutParams為wparams，即WindowManager.LayoutParams類型。最后調(diào)用root.setView()方法去通知 ?系統(tǒng)需要?jiǎng)?chuàng)建該窗口。我們接下來往下看看ViewRoot類相關(guān)操作。 ?? ? ??Step 3、 ? ? [java] view plaincopyprint?public?final?class?ViewRoot?extends?Handler?implements?ViewParent,View.AttachInfo.Callbacks?{?? ????????? ????View?mView;???//所有窗口地root?View????? ????final?WindowManager.LayoutParams?mWindowAttributes?=?new?WindowManager.LayoutParams();???? ?? ????...?? ?????/**? ?????*?We?have?one?child? ?????*/?? ????public?void?setView(View?view,?WindowManager.LayoutParams?attrs,?? ????????????View?panelParentView)?{?? ????????synchronized?(this)?{?? ????????????if?(mView?==?null)?{?? ????????????????mView?=?view;?? ????????????????mWindowAttributes.copyFrom(attrs);?//保存WindowManager.LayoutParams屬性值?? ????????????????attrs?=?mWindowAttributes;?? ????????????????...?? ?????????????????? ????????????????mAdded?=?true;?? ????????????????int?res;?/*?=?WindowManagerImpl.ADD_OKAY;?*/?? ?? ????????????????//?Schedule?the?first?layout?-before-?adding?to?the?window?? ????????????????//?manager,?to?make?sure?we?do?the?relayout?before?receiving?? ????????????????//?any?other?events?from?the?system.?? ????????????????requestLayout();???//請(qǐng)求UI開始繪制。?? ????????????????mInputChannel?=?new?InputChannel();??//創(chuàng)建一個(gè)InputChannel對(duì)象，接受消息?? ????????????????try?{?? ????????????????????//通知WindowManagerService添加一個(gè)窗口?? ????????????????????res?=?sWindowSession.add(mWindow,?mWindowAttributes,?? ????????????????????????????getHostVisibility(),?mAttachInfo.mContentInsets,?? ????????????????????????????mInputChannel);?? ????????????????}??? ????????????????...?? ????????????????view.assignParent(this);??//將root?View的父View設(shè)置為該ViewRoot對(duì)象(實(shí)現(xiàn)了ViewParent接口)?? ????????????????...?? ????????????}?? ????????}?? ????}?? }?? ? ? ?? ? ? 說明：ViewRoot類繼承了Handler，實(shí)現(xiàn)了ViewParent接口
? setView()方法地主要功能如下：
? ? ? ? 1、保存相關(guān)屬性值，例如：mView、mWindowAttributes等；
? ? ? ? 2、調(diào)用requestLayout()方法請(qǐng)求UI繪制，由于ViewRoot是個(gè)Handler對(duì)象，異步請(qǐng)求；
? ? ? ? 3、通知WindowManagerService添加一個(gè)窗口；
? ? ? ? 4、注冊(cè)一個(gè)事件監(jiān)聽管道，用來監(jiān)聽：按鍵(KeyEvent)和觸摸(MotionEvent)事件。
??我們這兒重點(diǎn)關(guān)注 requestLayout()方法請(qǐng)求UI繪制地流程。
??Step 4、異步調(diào)用請(qǐng)求UI繪制
? ? [java] view plaincopyprint?/**? ?*?{@inheritDoc}? ?*/?? public?void?requestLayout()?{?? ????checkThread();????????//檢查是不是UI線程調(diào)用，如果不是UI線程，會(huì)報(bào)異常?? ????mLayoutRequested?=?true;???//置為真，表示需要進(jìn)行measure和layout過程?? ????scheduleTraversals();???? }?? //開始UI繪制流程?? public?void?scheduleTraversals()?{?? ????if?(!mTraversalScheduled)?{?? ????????mTraversalScheduled?=?true;???????//防止多次調(diào)用?? ????????sendEmptyMessage(DO_TRAVERSAL);???//異步請(qǐng)求UI繪制?? ????}?? }?? @Override?? public?void?handleMessage(Message?msg)?{?? ?switch?(msg.what)?{?? ????????case?DO_TRAVERSAL:?? ?????????????performTraversals();??//開始UI繪制?? ?????????????break;?? ?}?? }?? ? ?
? ? ? ? ? 由于performTraversals()方法比較復(fù)雜，我們側(cè)重于第一次設(shè)置root View的widhtSpecSize以及 ? ?
? heightSpecSize值。
[java] view plaincopyprint? private?void?performTraversals()?{?? ????//?cache?mView?since?it?is?used?so?much?below...?? ????final?View?host?=?mView;?? ?? ????mTraversalScheduled?=?false;??????????? ????boolean?surfaceChanged?=?false;?? ????WindowManager.LayoutParams?lp?=?mWindowAttributes;???? ?? ????int?desiredWindowWidth;??????????????//表示該窗口期望width值?? ????int?desiredWindowHeight;?????????????//表示該窗口期望width值?? ????int?childWidthMeasureSpec;???????????//保存root?View的widthMeasureSpec?? ????int?childHeightMeasureSpec;??????????//保存root?View的heightMeasureSpec?? ?? ????final?View.AttachInfo?attachInfo?=?mAttachInfo;?? ?? ????final?int?viewVisibility?=?getHostVisibility();?? ????boolean?viewVisibilityChanged?=?mViewVisibility?!=?viewVisibility?? ????????????||?mNewSurfaceNeeded;?? ?? ????float?appScale?=?mAttachInfo.mApplicationScale;?? ?? ????WindowManager.LayoutParams?params?=?null;?? ????if?(mWindowAttributesChanged)?{?? ????????mWindowAttributesChanged?=?false;?? ????????surfaceChanged?=?true;?? ????????params?=?lp;?? ????}?? ????Rect?frame?=?mWinFrame;?? ????if?(mFirst)?{???//mFirst表示是否是第一次繪制該Window?? ????????fullRedrawNeeded?=?true;?? ????????mLayoutRequested?=?true;?? ?? ????????DisplayMetrics?packageMetrics?=?? ????????????mView.getContext().getResources().getDisplayMetrics();?? ????????//第一次繪制時(shí)desiredWindowWidth，desiredWindowHeight?值大小為屏幕大小?? ????????desiredWindowWidth?=?packageMetrics.widthPixels;?? ????????desiredWindowHeight?=?packageMetrics.heightPixels;?? ????????...?? ????}?else?{???//不是第一次繪制，則desiredWindowWidth值為frame保存大小，frame值會(huì)由WMS填充?? ????????desiredWindowWidth?=?frame.width();?? ????????desiredWindowHeight?=?frame.height();?? ????????...?? ????}?? ????...?? ????boolean?insetsChanged?=?false;?? ?? ????if?(mLayoutRequested)?{?? ????????...//獲得root?View的widthMeasureSpec?和?heightMeasureSpec值?? ????????childWidthMeasureSpec?=?getRootMeasureSpec(desiredWindowWidth,?lp.width);?? ????????childHeightMeasureSpec?=?getRootMeasureSpec(desiredWindowHeight,?lp.height);?? ????????//開始measure過程?? ????????host.measure(childWidthMeasureSpec,?childHeightMeasureSpec);?? ????}?? ????...?? ????final?boolean?didLayout?=?mLayoutRequested;?? ?????? ????boolean?triggerGlobalLayoutListener?=?didLayout?? ????????????||?attachInfo.mRecomputeGlobalAttributes;?? ????if?(didLayout)?{?? ????????...?//layout過程?? ???????host.layout(0,?0,?host.mMeasuredWidth,?host.mMeasuredHeight);?? ????????...?? ????}?? ????...?? ????if?(!cancelDraw?&&?!newSurface)?{?? ????????mFullRedrawNeeded?=?false;?? ????????draw(fullRedrawNeeded);?? ????????...?? }?? [java] view plaincopyprint? /**? ??*?@param?windowSize??The?available?width?or?height?of?the?window? ??*? ??*?@param?rootDimension?The?layout?params?for?one?dimension?(width?or?height)?of?the?window.? ?*/?? ?private?int?getRootMeasureSpec(int?windowSize,?int?rootDimension)?{?? ?????int?measureSpec;?? ?????switch?(rootDimension)?{?? ?????case?ViewGroup.LayoutParams.MATCH_PARENT:?? ?????????//?Window?can't?resize.?Force?root?view?to?be?windowSize.?? ?????????measureSpec?=?MeasureSpec.makeMeasureSpec(windowSize,?MeasureSpec.EXACTLY);?? ?????????break;?? ?????case?ViewGroup.LayoutParams.WRAP_CONTENT:?? ?????????//?Window?can?resize.?Set?max?size?for?root?view.?? ?????????measureSpec?=?MeasureSpec.makeMeasureSpec(windowSize,?MeasureSpec.AT_MOST);?? ?????????break;?? ?????default:?? ?????????//?Window?wants?to?be?an?exact?size.?Force?root?view?to?be?that?size.?? ?????????measureSpec?=?MeasureSpec.makeMeasureSpec(rootDimension,?MeasureSpec.EXACTLY);?? ?????????break;?? ?????}?? ?????return?measureSpec;?? ?}?????????
? ? ? 調(diào)用root View的measure()方法時(shí)，其參數(shù)是由getRootMeasureSpec()設(shè)置的，基本思路同我們前面描述的 ? 差不多。貼出來的代碼只是簡(jiǎn)簡(jiǎn)單單列出了measure 、layout 、 draw 過程的調(diào)用點(diǎn)，里面有很多邏輯處理， ? 閱讀起來比較費(fèi)勁，我也只能算是個(gè)囫圇吞棗水平。大家有興趣地可以看看源碼，加深理解。
? ??
? ? 最后，由于小子理解水平有限，可能很多地方讓大家“丈二和尚--摸不著頭腦”，給大家兩個(gè)小建議吧： ? ? ? ? ? ? 1、仔細(xì)鉆研源碼 ?； ? ? ? ? ? ? 2、想認(rèn)真系統(tǒng)性研讀UI繪制原理的話，建議詳細(xì)閱讀<<Android內(nèi)核剖析>>第十三章 <UI繪制原理> 《新程序員》：云原生和全面數(shù)字化實(shí)踐50位技術(shù)專家共同創(chuàng)作，文字、視頻、音頻交互閱讀
? ? ? ? 上篇文章<<Android中measure過程、WRAP_CONTENT詳解以及xml布局文件解析流程淺析(上)>>中，我們
? 了解了View樹的轉(zhuǎn)換過程以及如何設(shè)置View的LayoutParams的。本文繼續(xù)沿著既定軌跡繼續(xù)未完成的job。
? ? ? ? 主要知識(shí)點(diǎn)如下：
? ? ? ? ? ? ? ? ?1、MeasureSpc類說明
? ? ? ? ? ? ? ? ?2、measure過程詳解(揭秘其細(xì)節(jié));
? ? ? ? ? ? ? ? ?3、root View被添加至窗口時(shí)，UI框架是如何設(shè)置其LayoutParams值得。
? ? ? ?在講解measure過程前，我們非常有必要理解MeasureSpc類的使用，否則理解起來也只能算是囫圇吞棗。
?1、MeasureSpc類說明
? ?1.1 ?SDK 說明如下
? ? ? ? ? ? ? A MeasureSpec encapsulates the layout requirements passed from parent to child. Each MeasureSpec? ? ? ? ?represents a requirement for either the width or the height. A MeasureSpec is comprised of a size and
? ? ? ? ?a mode.
? ? ? ? 即：
? ? ? ? ? ? ?MeasureSpc類封裝了父View傳遞給子View的布局(layout)要求。每個(gè)MeasureSpc實(shí)例代表寬度或者高度
? ?(只能是其一)要求。?它有三種模式：
? ? ? ? ? ? ①、UNSPECIFIED(未指定)，父元素部隊(duì)自元素施加任何束縛，子元素可以得到任意想要的大小；
? ? ? ? ? ? ②、EXACTLY(完全)，父元素決定自元素的確切大小，子元素將被限定在給定的邊界里而忽略它本身大小；
? ? ? ? ? ? ③、AT_MOST(至多)，子元素至多達(dá)到指定大小的值。
? ?常用的三個(gè)函數(shù)：
static int getMode(int measureSpec) ?: ?根據(jù)提供的測(cè)量值(格式)提取模式(上述三個(gè)模式之一)
? ? ?static int getSize(int measureSpec) ?: 根據(jù)提供的測(cè)量值(格式)提取大小值(這個(gè)大小也就是我們通常所說的大小)
? ? ?static int makeMeasureSpec(int size,int mode) ?: ?根據(jù)提供的大小值和模式創(chuàng)建一個(gè)測(cè)量值(格式)
? ? ? ? ? ? ?以上摘取自: ?<<MeasureSpec介紹及使用詳解>>
? ?1.2 ? MeasureSpc類源碼分析???其為View.java類的內(nèi)部類，路徑：\frameworks\base\core\java\android\view\View.java
[java] view plaincopyprint?? ?? MeasureSpec類的處理思路是：
? ? ? ①、右移運(yùn)算，使int 類型的高兩位表示模式的實(shí)際值，其余30位表示其余30位代表長(zhǎng)或?qū)挼膶?shí)際值----可以是
? ? ? ? ?WRAP_CONTENT、MATCH_PARENT或具體大小exactly size。
? ? ? ②、通過掩碼MODE_MASK進(jìn)行與運(yùn)算 “&”，取得模式(mode)以及長(zhǎng)或?qū)?value)的實(shí)際值。
?2、measure過程詳解
?
? ?2.1 ?measure過程深入分析
? ? ? ?之前的一篇博文<<?Android中View繪制流程以及invalidate()等相關(guān)方法分析>>，我們從”二B程序員”的角度簡(jiǎn)單 ? ?解了measure過程的調(diào)用過程。過了這么多，我們也該升級(jí)了，- - 。現(xiàn)在請(qǐng)開始從”普通程序員”角度去理解這個(gè)
?過程。我們重點(diǎn)查看measure過程中地相關(guān)方法。
? ? ?我們說過，當(dāng)UI框架開始繪制時(shí)，皆是從ViewRoot.java類開始繪制的。
? ? ? ViewRoot類簡(jiǎn)要說明: 任何顯示在設(shè)備中的窗口，例如：Activity、Dialog等，都包含一個(gè)ViewRoot實(shí)例，該
? 類主要用來與遠(yuǎn)端 WindowManagerService交互以及控制(開始/銷毀)繪制。
? ? ?Step 1、 開始UI繪制 ， 具體繪制方法則是：
這兒，我并沒有說出childWidthMeasureSpec和childHeightMeasureSpec類的來由(為了避免額外地開銷，等到 第三部分時(shí)我們?cè)趤砉タ怂?#xff0c;現(xiàn)在只需要記住其值MeasureSpec.makeMeasureSpec()構(gòu)建的。
? ? Step 2 、調(diào)用measure()方法去做一些前期準(zhǔn)備
? ? ? ?measure()方法原型定義在View.java類中，final修飾符修飾，其不能被重載：
? ??
[java] view plaincopyprint?
? ? ??參數(shù)widthMeasureSpec和heightMeasureSpec?由父View構(gòu)建，表示父View給子View的測(cè)量要求。其值地構(gòu)建
?會(huì)在下面步驟中詳解。 ?
? ?measure()方法顯示判斷是否需要重新調(diào)用設(shè)置改View大小，即調(diào)用onMeasure()方法，然后操作兩個(gè)標(biāo)識(shí)符：
? ? ? ? ? ??①、重置MEASURED_DIMENSION_SET? ?： onMeasure()方法中，需要添加該標(biāo)識(shí)符，否則，會(huì)報(bào)異常； ? ?
? ? ? ?②、添加LAYOUT_REQUIRED ： 表示需要進(jìn)行l(wèi)ayout操作。
? ? 最后，保存當(dāng)前的widthMeasureSpec和heightMeasureSpec值。
?? Step 3 、調(diào)用onMeasure()方法去真正設(shè)置View的長(zhǎng)寬值，其默認(rèn)實(shí)現(xiàn)為：
[java] view plaincopyprint?
? ? ? ?主要功能就是根據(jù)該View屬性(android:minWidth和背景圖片大小)和父View對(duì)該子View的"測(cè)量要求"，設(shè)置該 ? ? ?View的?mMeasuredWidth 和?mMeasuredHeight 值。
? ? ? ?這兒只是一般的View類型地實(shí)現(xiàn)方法。一般來說，父View，也就是ViewGroup類型，都需要在重寫onMeasure() ? 方法，遍歷所有子View，設(shè)置每個(gè)子View的大小。基本思想如下：遍歷所有子View，設(shè)置每個(gè)子View的大小。偽
? 代碼表示為：
[java] view plaincopyprint?
? ? ??Step 2、Step 3?代碼也比較好理解，但問題是我們示例代碼中widthMeasureSpec、heightMeasureSpec是如何
?確定的呢？父View是如何設(shè)定其值的？
??
? ? ? 要想回答這個(gè)問題，我們看是去源代碼里找找答案吧。在ViewGroup.java類中，為我們提供了三個(gè)方法，去設(shè)置
每個(gè)子View的大小，基本思想也如同我們之前描述的思想：遍歷所有子View，設(shè)置每個(gè)子View的大小。
? ? ?主要有如下方法：
[java] view plaincopyprint?? ? ?measureChildren()方法：遍歷所有子View，調(diào)用measureChild()方法去設(shè)置該子View的屬性值。
? ? ?measureChild() ?方法 ? ： 獲取特定子View的widthMeasureSpec、heightMeasureSpec，調(diào)用measure()方法
?設(shè)置子View的實(shí)際寬高值。
? ??getChildMeasureSpec()就是獲取子View的widthMeasureSpec、heightMeasureSpec值。
??
[java] view plaincopyprint?? ? ? ?為了便于分析，我將上面的邏輯判斷語句使用列表項(xiàng)進(jìn)行了說明.
? getChildMeasureSpec()方法的主要功能如下：
? ? ? ??根據(jù)父View的measureSpec值(widthMeasureSpec,heightMeasureSpec)值以及子View的子View內(nèi)部
??LayoutParams屬性值，共同決定子View的measureSpec值的大小。主要判斷條件主要為MeasureSpec的mode
?類型以及LayoutParams的寬高實(shí)際值(lp.width,lp.height)，見于以上所貼代碼中的列表項(xiàng)： 1、 1.1 ; 1.2 ; 1.3 ;?
? 2、2.1等。
? ? ? ? 例如，分析列表3：假設(shè)當(dāng)父View為MeasureSpec.UNSPECIFIED類型，即未定義時(shí)，只有當(dāng)子View的width
?或height指定時(shí)，其mode才為MeasureSpec.EXACTLY，否者該View size為 0 ，mode為MeasureSpec.UNSPECIFIED時(shí)
?，即處于未指定狀態(tài)。
? ? ? 由此可以得出， 每個(gè)View大小的設(shè)定都事由其父View以及該View共同決定的。但這只是一個(gè)期望的大小，每個(gè)
?View在測(cè)量時(shí)最終大小的設(shè)定是由setMeasuredDimension()最終決定的。因此，最終確定一個(gè)View的“測(cè)量長(zhǎng)寬“是
?由以下幾個(gè)方面影響：
? ? ? ? 1、父View的MeasureSpec屬性；
? ? ? ? 2、子View的LayoutParams屬性 ；
? ? ? ? 3、setMeasuredDimension()或者其它類似設(shè)定?mMeasuredWidth 和?mMeasuredHeight 值的方法。
? ? ? ? ? ? ? ??setMeasuredDimension()原型：
[java] view plaincopyprint?
? 將上面列表項(xiàng)轉(zhuǎn)換為表格為：
? ? ? ? ? ? ? ? ? ? ? ? ? ? ??
? ?這張表格更能幫助我們分析View的MeasureSpec的確定條件關(guān)系。
? ?為了幫助大家理解，下面我們分析某個(gè)窗口使用地xml布局文件，我們弄清楚該xml布局文件中每個(gè)View的
MeasureSpec值的組成。
? ??
[java] view plaincopyprint?? ? ?該布局文件共有兩個(gè)View： ?①、id為llayout的LinearLayout布局控件 ;
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?②、id為tv的TextView控件。
? ? ? 假設(shè)LinearLayout的父View對(duì)應(yīng)地widthSpec和heightSpec值皆為MeasureSpec.EXACTLY類型(Activity窗口
? 的父View為DecorView，具體原因見第三部分說明)。
? ? ? ?對(duì)LinearLayout而言比較簡(jiǎn)單，由于 android:layout_width="match_parent"，因此其width對(duì)應(yīng)地widthSpec?
? mode值為MeasureSpec.EXACTLY ，?size由父視圖大小指定 ;??由于android:layout_height = "match_parent"，
? 因此其height對(duì)應(yīng)地heightSpec mode值為MeasureSpec.EXACTLY，size由父視圖大小指定 ;
? ? ? ?對(duì)TextView而言 ，其父View為L(zhǎng)inearLayout的widthSpec和heightSpec值皆為MeasureSpec.EXACTLY類型，
?由于android:layout_width="match_parent" ， 因此其width對(duì)應(yīng)地widthSpec mode值為MeasureSpec.EXACTLY，
?size由父視圖大小指定 ; ?由于android:layout_width="wrap_content" ， 因此其height對(duì)應(yīng)地widthSpec mode值為
?MeasureSpec.AT_MOST，size由父視圖大小指定 。
? ? 我們繼續(xù)窺測(cè)下LinearLayout類是如何進(jìn)行measure過程的：
[java] view plaincopyprint?
? ? ? ? ??
? ? ? ? 繼續(xù)看看measureChildWithMargins()方法，該方法定義在ViewGroup.java內(nèi)，基本流程同于measureChild()方法，但添加了對(duì)子View Margin的處理，即：android:margin屬性或者android:marginLeft等屬性的處理。
? ? ??measureChildWithMargins@ViewGroup.java?
[java] view plaincopyprint?
? ? measure()過程時(shí)，LinearLayout類做了如下事情 ：
? ? ? ? ? ? 1、遍歷每個(gè)子View，對(duì)其調(diào)用measure()方法；
? ? ? ? ? ? 2、子View?measure()完成后，需要取得該子View地寬高實(shí)際值，繼而做處理(例如：LinearLayout屬性為
? ? ? ?android:widht="wrap_content"時(shí)，LinearLayout的實(shí)際width值則是每個(gè)子View的width值的累加值)。
? ? ?
??2.2 WRAP_CONTENT、MATCH_PARENT以及measure動(dòng)機(jī)揭秘
? ? ? ? 子View地寬高實(shí)際值 ，即child.getMeasuredWidth()值得返回最終會(huì)是一個(gè)確定值？? 難道WRAP_CONTENT(
其值為-2)?、MATCH_PARENT(值為-1)或者說一個(gè)具體值(an exactly size > 0)。前面我們說過,View最終“測(cè)量”值的
確定是有三個(gè)部分組成地：
? ? ? ? ?①、父View的MeasureSpec屬性；
? ? ? ? ?②、子View的LayoutParams屬性 ；
? ? ? ? ?③、setMeasuredDimension()或者其它類似設(shè)定?mMeasuredWidth 和?mMeasuredHeight 值的方法。
? ?因此，一個(gè)View必須以某種合適地方法確定它地最終大小。例如，如下自定義View：
[java] view plaincopyprint?
?該View的mMeasuredWidth 和?mMeasuredHeight值。
? ? ? 對(duì)于TextView而言，如果它地mode不是Exactly類型 ， 它會(huì)根據(jù)一些屬性，例如：android:textStyle
? 、android:textSizeandroid:typeface等去確定TextView類地需要占用地長(zhǎng)和寬。
? ?
? ? ?因此，如果你地自定義View必須手動(dòng)對(duì)不同mode做出處理。否則，則是mode對(duì)你而言是無效的。
? ?
? ? ? Android框架中提供地一系列View/ViewGroup都需要去進(jìn)行這個(gè)measure()過程地 ，因?yàn)樵趌ayout()過程中，父
? View需要調(diào)用getMeasuredWidth()或getMeasuredHeight()去為每個(gè)子View設(shè)置他們地布局坐標(biāo)，只有確定布局
? 坐標(biāo)后，才能真正地將該View 繪制(draw)出來，否則該View的layout大小為0，得不到期望效果。我們繼續(xù)看看
? LinearLayout的layout布局過程：
[java] view plaincopyprint?? ? ? 對(duì)一個(gè)View進(jìn)行measure操作地主要目的就是為了確定該View地布局大小，見上面所示代碼。但measure操作
?通常是耗時(shí)的，因此對(duì)自定義ViewGroup而言，我們可以自由控制measure、layout過程，如果我們知道如何layout
?一個(gè)View，我們可以跳過該ViewGroup地measure操作(onMeasure()方法中measure所有子View地)，直接去layout
? ? ? 在前面一篇博客<<Android中滑屏初探 ---- scrollTo 以及 scrollBy方法使用說明>>中，我們自定義了一個(gè) ? ? ViewGroup, ?并且重寫了onMeasure()和onLayout()方法去分別操作每個(gè)View。就該ViewGroup而言，我們只需要
??重寫onLayout()操作即可，因?yàn)槲覀冎廊绾蝜ayout每個(gè)子View。如下代碼所示：
? ? ?更多關(guān)于自定義ViewGroup無須重寫measure動(dòng)作的，可以參考 Android API ：
? ? ? ? ? ? ? ?<<Optimizing the View?>>
? ? ?中文翻譯見于：<<?Android中View繪制優(yōu)化之三---- 優(yōu)化View>>
?3、root View被添加至窗口時(shí)，UI框架是如何設(shè)置其LayoutParams值
? ? ? ? ?老子道德經(jīng)有言：“道生一，一生二，二生三，三生萬物。” ?UI繪制也就是個(gè)遞歸過程。理解其基本架構(gòu)后， ?也就“掌握了一個(gè)中心點(diǎn)”了。在第一節(jié)中，我們沒有說明開始UI繪制時(shí) ，沒有說明mView.measure()參數(shù)地由來， ?參數(shù)也就是我們本節(jié)需要弄懂的“道” --- root View的 widthMeasureSpec和heightMeasureSpec?是如何確定的。
? ?對(duì)于如下布局文件： main.xml [java] view plaincopyprint?
? ? 任何一個(gè)View被添加至窗口時(shí)，都需要利用WindowManager類去操作。例如，如下代碼： ? [java] view plaincopyprint?
[java] view plaincopyprint?
?Step 2 、?獲得WindowManagerImpl的單例對(duì)象，以及部分源碼分析 ? ? ? ? ? ?路徑：?/frameworks/base/core/java/android/view/WindowManagerImpl.java? [java] view plaincopyprint?
? ? ??WindowManagerImpl類的三個(gè)數(shù)組集合保存了每個(gè)窗口相關(guān)屬性，這樣我們可以通過這些屬性去操作特定的 ?窗口(例如，可以根據(jù)View去更新/銷毀該窗口)。當(dāng)參數(shù)檢查成功時(shí)，構(gòu)建一個(gè)ViewRoot對(duì)象，并且設(shè)置設(shè)置root ?View 的LayoutParams為wparams，即WindowManager.LayoutParams類型。最后調(diào)用root.setView()方法去通知 ?系統(tǒng)需要?jiǎng)?chuàng)建該窗口。我們接下來往下看看ViewRoot類相關(guān)操作。 ?? ? ??Step 3、 ? ? [java] view plaincopyprint?
? setView()方法地主要功能如下：
? ? ? ? 1、保存相關(guān)屬性值，例如：mView、mWindowAttributes等；
? ? ? ? 2、調(diào)用requestLayout()方法請(qǐng)求UI繪制，由于ViewRoot是個(gè)Handler對(duì)象，異步請(qǐng)求；
? ? ? ? 3、通知WindowManagerService添加一個(gè)窗口；
? ? ? ? 4、注冊(cè)一個(gè)事件監(jiān)聽管道，用來監(jiān)聽：按鍵(KeyEvent)和觸摸(MotionEvent)事件。
??我們這兒重點(diǎn)關(guān)注 requestLayout()方法請(qǐng)求UI繪制地流程。
??Step 4、異步調(diào)用請(qǐng)求UI繪制
? ? [java] view plaincopyprint?
? ? ? 調(diào)用root View的measure()方法時(shí)，其參數(shù)是由getRootMeasureSpec()設(shè)置的，基本思路同我們前面描述的 ? 差不多。貼出來的代碼只是簡(jiǎn)簡(jiǎn)單單列出了measure 、layout 、 draw 過程的調(diào)用點(diǎn)，里面有很多邏輯處理， ? 閱讀起來比較費(fèi)勁，我也只能算是個(gè)囫圇吞棗水平。大家有興趣地可以看看源碼，加深理解。
? ??
? ? 最后，由于小子理解水平有限，可能很多地方讓大家“丈二和尚--摸不著頭腦”，給大家兩個(gè)小建議吧： ? ? ? ? ? ? 1、仔細(xì)鉆研源碼 ?； ? ? ? ? ? ? 2、想認(rèn)真系統(tǒng)性研讀UI繪制原理的話，建議詳細(xì)閱讀<<Android內(nèi)核剖析>>第十三章 <UI繪制原理> 《新程序員》：云原生和全面數(shù)字化實(shí)踐50位技術(shù)專家共同創(chuàng)作，文字、視頻、音頻交互閱讀
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