android - 为什么 MeasuredHeight 总是 0，我怎样才能得到这个值？

Question

我正在尝试应用动画来折叠 LinearLayout。此动画取决于 LinearLayout 的 MeasuredHeight 属性，其值大于 0，但该值始终为 0。

这是我正在使用的代码：

    public void Collapse()
    {
        var v = FindViewById<LinearLayout>(Resource.Id.layoutBranding);
        int initialHeight = v.MeasuredHeight; // always 0!!

        var a = new MyAnimation(v, initialHeight);

        a.Duration = (int)(initialHeight / v.Context.Resources.DisplayMetrics.Density);
        v.StartAnimation(a);
    }

其中 MyAnimation 定义为：

public class MyAnimation : Animation { private readonly View _view; 私有只读 int _initialHeight;

    public MyAnimation(View view, int initalHeight)
    {
        _view = view;
        _initalHeight = initalHeight;
    }

    protected override void ApplyTransformation(float interpolatedTime, Transformation t)
    {
        if (interpolatedTime == 1)
        {
            _view.Visibility = ViewStates.Gone;
        }
        else
        {
            _view.LayoutParameters.Height = _initalHeight - (int) (_initalHeight*interpolatedTime);
            _view.RequestLayout();
        }
    }

    public override bool WillChangeBounds()
    {
        return true;
    }
}

Answer 1

尝试这个：

v.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);


int initialHeight = v.MeasuredHeight; 

Answer 2

尝试测量视图的高度和宽度 -

    @Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);
        if(hasFocus)
        {
            // Get the height and the width of the view 
        }
    }

Answer 3

在 View 真正布局之前（就在渲染之前），它的高度和宽度始终为 0

如果你测量onMeasure或onLayout（我认为）的高度，那么它应该有一个非零高度