ViewModel 不应该引用视图。如果你这样做，那么你会得到内存泄漏。如何不违反这个规则？

Question

A ViewModel must never reference a view, Lifecycle, or any class that may hold a reference to the activity context.

View model should never reference a view. If you do, then you'll get memory leaks.

public class FirstActivityViewModel extends ViewModel {

    private int displayWidth;
    private int displayHeight;

    private double widthMultiplier;
    private double heightMultiplier;

    private int testedWidth = 1200;
    private int testedHeight = 1920;

    public void setDisplayCorrectedSizes(RelativeLayout relativeLayout){
        displayWidth = relativeLayout.getWidth();
        widthMultiplier = ((double) displayWidth) / ((double) testedWidth);

        displayHeight = relativeLayout.getHeight();
        heightMultiplier = ((double) displayHeight) / ((double) testedHeight);
    }

    public double getWidthMultiplier(){
        return widthMultiplier;
    }

    public double getHeightMultiplier(){
        return heightMultiplier;
    }
}

或者这样的代码违反了该规则？

public class FirstActivityViewModel extends ViewModel {

    private RelativeLayout relativeLayout;

    private int displayWidth;
    private int displayHeight;

    private double widthMultiplier;
    private double heightMultiplier;

    private int testedWidth = 1200;
    private int testedHeight = 1920;

    public void setDisplayCorrectedSizes(RelativeLayout relativeLayout){
        displayWidth = relativeLayout.getWidth();
        widthMultiplier = ((double) displayWidth) / ((double) testedWidth);

        displayHeight = relativeLayout.getHeight();
        heightMultiplier = ((double) displayHeight) / ((double) testedHeight);
        
        this.relativeLayout = relativeLayout;
    }

    public double getWidthMultiplier(){
        return widthMultiplier;
    }

    public double getHeightMultiplier(){
        return heightMultiplier;
    }
}

或者两者都违规？

我只是想了解我是否以正确的方式理解它。

........................................

这是我想从视图替换为 ViewModel 的全部代码。

 void actionsForUISizesOptimizationProcess(){
        RelativeLayout relativeLayout2 = findViewById(R.id.rootLayoutSmallBoard);

       
        int displayWidth = relativeLayout2.getWidth();
        int displayHeight = relativeLayout2.getHeight();

        
        int testedWidth = 1200;
        double widthMultiplier = ((double) displayWidth) / ((double) testedWidth);
        int testedHeight = 1920;
        double heightMultiplier = ((double) displayHeight) / ((double) testedHeight);

//        firstActivityViewModel.setDisplayCorrectedSizes(relativeLayout2);
//        double widthMultiplier = firstActivityViewModel.getWidthMultiplier();
//        double heightMultiplier = firstActivityViewModel.getHeightMultiplier();

        if (limitOfOnWindowFocusChangedOperationForSmallBoard == 0) { /

            //Log.i("userTest2020", "display width = " + displayWidth + "\n" + "display height = " + displayHeight);

            int viewWidth;
            int viewHeight;

            viewWidth = (int) getResources().getDimension(R.dimen.tv10WidthSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.tv10HeightSmallBoard);

            tvSmallBoardResolutionInfoValue.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            tvSmallBoardResolutionInfoValue.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            viewWidth = (int) getResources().getDimension(R.dimen.tv11WidthSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.tv11HeightSmallBoard);

            tvSmallBoardScoreValue.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            tvSmallBoardScoreValue.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            viewWidth = (int) getResources().getDimension(R.dimen.btn1WidthSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.btn1HeightSmallBoard);

            btnSmallBoardGetTheResolutionInfo.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            btnSmallBoardGetTheResolutionInfo.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            viewWidth = (int) getResources().getDimension(R.dimen.btnNewRoundWidthSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.btnNewRoundHeightSmallBoard);

            btnNewRoundSmallBoard.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            btnNewRoundSmallBoard.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            ImageView ivBtnGreen = findViewById(R.id.ivNewRoundSmallBoard);
            viewWidth = (int) getResources().getDimension(R.dimen.ivNewRoundWidthSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.ivNewRoundHeightSmallBoard);

            ivBtnGreen.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            ivBtnGreen.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

           
            FrameLayout flNewBoard = findViewById(R.id.newRoundViewGroupSmallBoard);
            viewWidth = flNewBoard.getWidth();
            viewHeight = flNewBoard.getHeight();

            flNewBoard.getLayoutParams().width = (int) (viewWidth * widthMultiplier);
            flNewBoard.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            FrameLayout flBiggerBoard = findViewById(R.id.biggerBoardViewGroupSmallBoard);
            viewWidth = (int) getResources().getDimension(R.dimen.BiggerBoardViewGroupSmallBoard);

            flBiggerBoard.getLayoutParams().width = (int) (viewWidth * widthMultiplier);

            viewHeight = (int) getResources().getDimension(R.dimen.btnNextBoardHeightSmallBoard);

            btnNextBoardSmallBoard.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            ImageView ivNextBoard = findViewById(R.id.ivNextBoardSmallBoard);
            viewHeight = (int) getResources().getDimension(R.dimen.ivNextBoardHeightSmallBoard);

            ivNextBoard.getLayoutParams().height = (int) (viewHeight * heightMultiplier);

            limitOfOnWindowFocusChangedOperationForSmallBoard = 1; 
        }
    }

为什么我认为我必须将此代码替换为 ViewModel？看这里https://android.jlelse.eu/mvvm-how-view-and-viewmodel-should-communicate-8a386ce1bb42（第一条规则）为什么我不知道该怎么做？另一方面，还有另一条规则：视图模型不应该引用视图。如果你这样做，那么你会得到内存泄漏。

Answer 1

在避免内存泄漏方面，您的第二个 FirstActivityViewModel 违反了规则。您有一个 Java 字段，其中包含对 RelativeLayout 的引用。如果 FirstActivity 由于配置更改而被销毁并重新创建，直到 setDisplayCorrectedSizes() 被第二个 activity 实例调用，您的视图模型正在泄漏第一个 activity 实例。

更一般地说，我会避免使用这两种方法中的任何一种。 viewmodel 负责准备要呈现到屏幕的数据，但是关于像素和大小的问题是 UI 层的工作，而不是 viewmodel，恕我直言。

此外，FWIW，您可能希望迁移到 ConstraintLayout，因为它比 RelativeLayout 更强大且维护得更好。

Answer 2

理论上，第二个违反规则而第一个不违反规则，但理想情况下，viewModel 永远不应该关心视图。在编写单元测试时，使用相对布局作为参数会出现问题。我们的目标应该是尽可能将 viewModel 与 view 分开。我建议像这样重写你的第二种方法

public void setDisplayCorrectedSizes(int displayWidth, int displayHeight){
    widthMultiplier = ((double) displayWidth) / ((double) testedWidth);
    heightMultiplier = ((double) displayHeight) / ((double) testedHeight);
}

另一个建议是将 getter 方法替换为发出值供视图观察的可观察对象。我会像这样重写你的 viewModel

public class FirstActivityViewModel extends ViewModel {

    private LiveData<Double> widthMultiplierLiveData = new MutableLiveData();
    private LiveData<Double> heightMultiplierLiveData = new MutableLiveData();
    
    private final int testedWidth = 1200;
    private final int testedHeight = 1920;

    public void setDisplayCorrectedSizes(int displayWidth, int displayHeight){
        double widthMultiplier = ((double) displayWidth) / ((double) testedWidth);
        double heightMultiplier = ((double) displayHeight) / ((double) testedHeight);
        
        widthMultiplierLiveData.value = widthMultiplier;
        heightMultiplierLiveData.value = heightMultiplier;
    }
}

ViewModel 不应该引用视图。如果你这样做，那么你会得到内存泄漏。如何不违反这个规则？

ViewModel should never reference a view. If you do, then you'll get memory leaks. How to not violate this rule?

android

memory-leaks

mvvm

viewmodel