Room實(shí)體類構(gòu)造函數(shù)異常

本案例是Entity無(wú)主構(gòu)造函數(shù)，多次構(gòu)造函數(shù)的情況。

異常描述：Room cannot pick a constructor since multiple constructors are suitable. Try to annotate unwanted constructors with @Ignore.

異常源代碼：

//創(chuàng)建數(shù)據(jù)庫(kù)實(shí)體 Entity @Entity(tableName = "User")//數(shù)據(jù)庫(kù)實(shí)體類 class User{//主鍵 自增@PrimaryKey(autoGenerate = true)var id:Int = 0@ColumnInfo(name="user_name") //實(shí)際數(shù)據(jù)庫(kù)中的字段user_namevar name:String = ""@ColumnInfo(name = "user_gender")var gender:String = ""var age:Int = 0constructor(id:Int,name:String,gender:String,age:Int) {this.id = idthis.name = namethis.gender = genderthis.age = age}constructor(name:String,gender: String,age:Int){this.name = namethis.gender = genderthis.age = age} }

異常原因：屬性有初始值，有兩個(gè)次構(gòu)造函數(shù)，系統(tǒng)認(rèn)為這兩個(gè)都適用，導(dǎo)致系統(tǒng)在創(chuàng)建對(duì)象里無(wú)法選擇構(gòu)造函數(shù)。

解決方案：

方案一，在次構(gòu)造函數(shù)上添加@ignore注解，只保留一個(gè)次構(gòu)造函數(shù)不添加。

//創(chuàng)建數(shù)據(jù)庫(kù)實(shí)體 Entity @Entity(tableName = "User")//數(shù)據(jù)庫(kù)實(shí)體類 class User{//主鍵 自增@PrimaryKey(autoGenerate = true)var id:Int = 0@ColumnInfo(name="user_name") //實(shí)際數(shù)據(jù)庫(kù)中的字段user_namevar name:String = ""@ColumnInfo(name = "user_gender")var gender:String = ""var age:Int = 0@Ignoreconstructor(id:Int,name:String,gender:String,age:Int) {this.id = idthis.name = namethis.gender = genderthis.age = age}constructor(name:String,gender: String,age:Int){this.name = namethis.gender = genderthis.age = age} }

方案二，添加主構(gòu)造函數(shù)，可以不帶參數(shù)的和帶參數(shù)的，次構(gòu)造函數(shù)得指向主構(gòu)造函數(shù)。下面示例使用不帶參數(shù)。

//創(chuàng)建數(shù)據(jù)庫(kù)實(shí)體 Entity @Entity(tableName = "User")//數(shù)據(jù)庫(kù)實(shí)體類 class User(){//主鍵 自增@PrimaryKey(autoGenerate = true)var id:Int = 0@ColumnInfo(name="user_name") //實(shí)際數(shù)據(jù)庫(kù)中的字段user_namevar name:String = ""@ColumnInfo(name = "user_gender")var gender:String = ""var age:Int = 0constructor(id:Int,name:String,gender:String,age:Int) : this() {this.id = idthis.name = namethis.gender = genderthis.age = age}constructor(name:String,gender: String,age:Int) : this() {this.name = namethis.gender = genderthis.age = age} }

ok,以上。

總結(jié)，

kotlin類，不寫主、次構(gòu)造函數(shù)。編譯java類會(huì)自動(dòng)生成默認(rèn)的構(gòu)造函數(shù)

kotlin類，不寫主構(gòu)造函數(shù)，寫次構(gòu)造函數(shù)。需要保證不能讓系統(tǒng)識(shí)別多個(gè)都適合，編譯java類不會(huì)自動(dòng)生成默認(rèn)主構(gòu)造函數(shù)

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