android - 为什么 MeasuredHeight 始终为 0，如何获取该值？

Question

我正在尝试应用动画来折叠 LinearLayout。此动画依赖于 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);
    }

MyAnimation 定义为:

公共(public)类 MyAnimation :动画 { 私有(private)只读 View _view； 私有(private)只读 int _initalHeight;

    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

试试这个:

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


int initialHeight = v.MeasuredHeight;