屏幕旋转时ViewModel不保留数据

如何解决屏幕旋转时ViewModel不保留数据

我将自己放在从Java到Kotlin的RecycleView中。我正在尝试在屏幕旋转之间保持状态。但这是行不通的。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会被弃用（使用注释的行），而在另一个具有类似gradle依赖关系的项目中却可以。

谢谢！

解决方法

每次使用ViewModelProvider.NewInstanceFactory().create都会创建一个新实例-这永远不是正确的选择。相反，请遵循ViewModelProviders.of() deprecation message：

使用by viewModels() Kotlin属性委托或ViewModelProvider(ViewModelStoreOwner)来传递活动。

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