视图模型在屏幕旋转时不保留数据

Question

我把自己放在从Java到Kotlin的RecycleView中。我试图在屏幕旋转之间保持状态。但它不起作用。这是我的代码：

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
//import androidx.lifecycle.ViewModelProviders
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity() {
private lateinit var viewModel: ScoreViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel = ViewModelProvider.NewInstanceFactory().create(ScoreViewModel::class.java)
//viewModel  = ViewModelProviders.of(this).get(ScoreViewModel::class.java)
println("-> "+viewModel.scoreTeamA);
}
fun addOneForTeamA(view: View) {
viewModel.scoreTeamA++
displayForTeamA()
}
fun addTwoForTeamA(view: View) {
viewModel.scoreTeamA += 2
displayForTeamA()
}
fun addThreeForTeamA(view: View) {
viewModel.scoreTeamA += 3
displayForTeamA()
}
fun addOneForTeamB(view: View) {
++viewModel.scoreTeamB
displayForTeamB()
}
fun addTwoForTeamB(view: View) {
viewModel.scoreTeamB += 2
displayForTeamB()
}
fun addThreeForTeamB(view: View) {
viewModel.scoreTeamB += 3
displayForTeamB()
}
fun displayForTeamA(){
team_a_score.text = viewModel.scoreTeamA.toString()
}
fun displayForTeamB(){
team_b_score.text = viewModel.scoreTeamB.toString()
}
fun resetScore(view: View) {
viewModel.scoreTeamA = 0
viewModel.scoreTeamB = 0
displayForTeamA()
displayForTeamB()
}
}


import androidx.lifecycle.ViewModel

class ScoreViewModel : ViewModel() {
var scoreTeamA: Int = 0
var scoreTeamB: Int = 0

}

另一个问题是，为什么在一个项目中ViewModelProviders.of显示为不推荐使用(se注释行(，而在另一个具有类似渐变依赖关系的项目中，它是可以的。

提前感谢！

Answer 1

每次使用ViewModelProvider.NewInstanceFactory().create都会创建一个新实例——这从来都不是正确的使用方法。相反，请遵循ViewModelProviders.of((的弃用消息：

使用by viewModels()Kotlin属性delegate或ViewModelProvider(ViewModelStoreOwner)，传入活动。

viewModel  = new ViewModelProvider(this).get(ScoreViewModel::class.java)