主要實現刻度尺的效果，能夠快速滑動刻度，設置刻度間距，刻度值，滑動回調。簡單易用

效果圖

textureView控件的選擇

總結來說:

1.view的繪制在主線程里面，頻繁繪制會導致主線程阻塞

2.我們知道一個surfaceview是異步繪制的，不阻塞主線程，但是它不支持平移、縮放、旋轉，且很難放在srollview等控件里面

TextureView.SurfaceTextureListener

abstract void

Invoked when a

abstract boolean

Invoked when the specified

is about to be destroyed.

//textureview銷毀時，可以在這個地方釋放一些資源，比如camera

abstract void

Invoked when the

abstract void

@Override

public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {

mBorderRectF.set(mBorderPaint.getStrokeWidth(), mBorderPaint.getStrokeWidth(),

width - mBorderPaint.getStrokeWidth(), height - mBorderPaint.getStrokeWidth()); //設置一塊矩形區域，

mWidth = mBorderRectF.width();

dis = (int)(mWidth / allBlockNum); //每個刻度間距,allBlockNum是小刻度的個數

refreshCanvas();

}

//刷新視圖

private void refreshCanvas() {

if (mBorderRectF.isEmpty()) {

return;

}

Canvas canvas = lockCanvas();

if(canvas != null) {

canvas.drawColor(Color.WHITE);

drawBorder(canvas);

drawScaleMark(canvas);

drawMarkPoint(canvas);

}

unlockCanvasAndPost(canvas);

}

畫出刻度線:由中間向兩邊畫

//畫出所有刻度:從中間向兩邊畫

private void drawScaleMark(Canvas canvas) {

int count = 0;

final int centerX = (int)mBorderRectF.centerX();

if(mCenterNum > maxNum)

mCenterNum = maxNum;

if (mCenterNum < minNum)

mCenterNum = minNum;

if(numberListener != null)

numberListener.onChanged(mCenterNum);

while(true){

int left = centerX - dis * count;

int leftNum = mCenterNum - count * scaleNum;

int right = centerX + dis * count;

int rightNum = mCenterNum + count * scaleNum;

String leftText = String.valueOf(leftNum);

String rightText = String.valueOf(rightNum);

//間隔5刻度畫文字信息

if(leftNum % (5*scaleNum) == 0) {

canvas.drawLine(left, canvas.getHeight() / 2, left, canvas.getHeight() - 1, mScaleMarkPaint);

mScaleMarkPaint.getTextBounds(leftText, 0, leftText.length(), mTextRect);

canvas.drawText(leftText, left - mTextRect.centerX(), canvas.getHeight() / 2, mScaleMarkPaint);

}

else

canvas.drawLine(left, canvas.getHeight() * 2 / 3, left, canvas.getHeight() - 1, mScaleMarkPaint);

if(rightNum % (5*scaleNum) == 0) {

canvas.drawLine(right, canvas.getHeight() / 2, right, canvas.getHeight() - 1, mScaleMarkPaint);

mScaleMarkPaint.getTextBounds(rightText, 0, rightText.length(), mTextRect);

canvas.drawText(rightText, right - mTextRect.centerX(), canvas.getHeight() / 2, mScaleMarkPaint);

}

else

canvas.drawLine(right, canvas.getHeight() * 2 / 3, right, canvas.getHeight() - 1, mScaleMarkPaint);

count++;

if(left < 0)

break;

}

}

手勢判斷

我把手勢判斷的邏輯代碼寫在ScaleScroller類中，onTouchEvent用來判斷按下，移動和抬起三個手勢。GestureDetector.SimpleOnGestureListener中的onFling來處理快速滑動

OnFling在手指快速滑動控件時觸發，onfling有四個參數

(注意:onFling只能觸發一次,但是快速滑動的效果是要在一定時間內做滾動處理，所以需要通過Scroller類+Handler的方式來幫助實現)

@Override

public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {

final int minX = -0x7fffffff;

final int maxX = 0x7fffffff;

lastX = 0;

scroller.fling(0, 0, (int)-velocityX, 0, minX, maxX, 0, 0); //滾動的距離有速度決定

handler.sendEmptyMessage(ON_FLING);

return true;

}

e1

The first down motion event that started the fling.?????? //按下時候的event

e2

The move motion event that triggered the current onFling.? //觸發快速滑動時的event

velocityX

The velocity of this fling measured in pixels per second along the x axis.

velocityY

The velocity of this fling measured in pixels per second along the y axis.

private Handler handler = new Handler(){

@Override

public void handleMessage(Message msg) {

boolean isFinished = scroller.computeScrollOffset(); //判斷滾動是否結束

int curX = scroller.getCurrX();

int delta = lastX - curX;

if(listener != null){

listener.onScroll(delta);

}

lastX = curX;

if(isFinished)

handler.sendEmptyMessage(ON_FLING);

else

listener.onFinished();

}

};

總結

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