旋转 Dragshadow（Xamarin，Android）

Question

我有一个旋转的文本视图，我想拖放这个视图。问题是拖动阴影没有旋转。

我在 java 中找到了 android 的解决方案，但这对我不起作用。可能是我翻译错了代码

How to drag a rotated DragShadow?

class CustomDragShdowBuilder : View.DragShadowBuilder
{
    private View _view;
    public CustomDragShdowBuilder(View view)
    {
        _view = view;
    }

    public override void OnDrawShadow(Canvas canvas)
    {
        double rotationRad = Math.ToRadians(_view.Rotation);
        int w = (int)(_view.Width * _view.ScaleX);
        int h = (int)(_view.Height * _view.ScaleY);
        double s = Math.Abs(Math.Sin(rotationRad));
        double c = Math.Abs(Math.Cos(rotationRad));

        int width = (int)(w * c + h * s);
        int height = (int)(w * s + h * c);

        canvas.Scale(_view.ScaleX, _view.ScaleY, width / 2, height / 2);
        canvas.Rotate(_view.Rotation, width / 2, height / 2);
        canvas.Translate((width - _view.Width) / 2, (height - _view.Height) / 2);

        base.OnDrawShadow(canvas);
    }

    public override void OnProvideShadowMetrics(Point shadowSize, Point shadowTouchPoint)
    {
        shadowTouchPoint.Set(shadowSize.X / 2, shadowSize.Y / 2);
        base.OnProvideShadowMetrics(shadowSize, shadowTouchPoint);
    }
}

Answer 1

I found a solution for android in java but this does not work for me. Maybe I translate the code wrong

是的，你翻译错了，你确实改了OnDrawShadow的代码但是你没有注意OnProvideShadowMetrics，目的是改变[=22=的大小] 绘图区域，所以需要传入相同的宽高，代码已经计算出来了：

这里是 DragShdowBuilder 的修改版本：

public class MyDragShadowBuilder : DragShadowBuilder
{
    private int width, height;

    // Defines the constructor for myDragShadowBuilder
    public MyDragShadowBuilder(View v) : base(v)
    {
    }

    // Defines a callback that sends the drag shadow dimensions and touch point back to the system.
    public override void OnProvideShadowMetrics(Android.Graphics.Point outShadowSize, Android.Graphics.Point outShadowTouchPoint)
    {
        double rotationRad = Java.Lang.Math.ToRadians(View.Rotation);
        int w = (int)(View.Width * View.ScaleX);
        int h = (int)(View.Height * View.ScaleY);
        double s = Java.Lang.Math.Abs(Java.Lang.Math.Sin(rotationRad));
        double c = Java.Lang.Math.Abs(Java.Lang.Math.Cos(rotationRad));


        //calculate the size of the canvas 
        //width = view's width*cos(rad)+height*sin(rad)
        width = (int)(w * c + h * s);
        //height = view's width*sin(rad)+height*cos(rad)
        height = (int)(w * s + h * c);

        outShadowSize.Set(width, height);

        // Sets the touch point's position to be in the middle of the drag shadow
        outShadowTouchPoint.Set(outShadowSize.X / 2, outShadowSize.Y / 2);
    }

    // Defines a callback that draws the drag shadow in a Canvas that the system constructs
    // from the dimensions passed in onProvideShadowMetrics().
    public override void OnDrawShadow(Canvas canvas)
    {

        canvas.Scale(View.ScaleX, View.ScaleY, width/2 , height/2);
        //canvas.DrawColor(Android.Graphics.Color.White);
        canvas.Rotate(View.Rotation,width/2, height / 2);
        canvas.Translate((width - View.Width)/2, (height - View.Height) / 2);
        base.OnDrawShadow(canvas);
    }

}

这是完整的示例：RotatedTextViewSample

旋转 Dragshadow（Xamarin，Android）

Rotated Dragshadow (Xamarin, Android)

android

rotation

dropshadow

xamarin