Xamarin Imageview Drag Sample

问题

(Xamarin with Visual Studio 2015 ) I want to implement a simple Activity inwith an Imageview, which can be moved/dragged with touch: This is what I have implemented, but the Image is flickering and moving slower. Can you give me an example how to implement this? Thanks for your help!

    private void TouchMeImageViewOnTouch(object sender, View.TouchEventArgs touchEventArgs)
    {
        View bild = (View)sender;
        RelativeLayout.LayoutParams layouti = (RelativeLayout.LayoutParams)bild.LayoutParameters;
        switch (touchEventArgs.Event.Action & MotionEventActions.Mask)
        {
            case MotionEventActions.Down:
                xDelta = touchEventArgs.Event.GetX()-layouti.LeftMargin;
                yDelta = touchEventArgs.Event.GetX() - layouti.LeftMargin;
                break;
            case MotionEventActions.Move:
                int wert = (int)touchEventArgs.Event.GetX();
                yvalue = touchEventArgs.Event.GetY()-yDelta;
                xvalue = touchEventArgs.Event.GetX()-xDelta;
                float xdpi = (int) Resources.DisplayMetrics.Density;
                layouti.LeftMargin = (int)xvalue;
                layouti.TopMargin = (int)yvalue;
                container.Invalidate();
                break;

            case MotionEventActions.Up:
                break;

            default:
                break;
        }

        xPositionText.Text = xvalue.ToString();
        yPositionText.Text = yvalue.ToString();
    }

回答1:

I have tried to implement a dragable imageview for testing. the drag is slow in the android emulator. But by testing it in the real device it works fine and move fast.

Try the following code sample：

public class MainActivity : Activity, IOnTouchListener
{
    Button dragAbleBt;
    ImageView imgV1;
    int screenWidth = 0;
    int screenHeight = 0;
    int lastX = 0, lastY = 0;
    public bool OnTouch(View v, MotionEvent e)
    {

        MotionEventActions ea = e.Action;
        switch (ea) {
            case MotionEventActions.Down:
                lastX = (int)e.RawX;
                lastY = (int)e.RawY;                
                break;
            case MotionEventActions.Move:
                int dx = (int)e.RawX - lastX;
                int dy = (int)e.RawY - lastY;
                int left = v.Left + dx;
                int right = v.Right + dx;
                int top = v.Top + dy;
                int bottom = v.Bottom + dy;
                if (left < 0)
                {
                    left = 0;
                    right = left + v.Width;
                }
                if (right > screenWidth)
                {
                    right = screenWidth;
                    left = right - v.Width;
                }
                if (top < 0)
                {
                    top = 0;
                    bottom = top + v.Height;
                }
                if (bottom > screenHeight)
                {
                    bottom = screenHeight;
                    top = bottom - v.Height;
                }
                v.Layout(left, top, right, bottom);
                lastX = (int) e.RawX;
                lastY = (int) e.RawY;
                v.PostInvalidate();
                break;
            case MotionEventActions.Up:                  
                break;                   
        }
        if (v.Id == Resource.Id.imageView1)
        {
            return true;
        }
        return false;
    }
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView (Resource.Layout.Main);
        //DisplayMetrics dm = Resources.DisplayMetrics;
        //screenWidth = dm.WidthPixels;
        //screenHeight = dm.HeightPixels;
        dragAbleBt = FindViewById<Button>(Resource.Id.button1);
        imgV1 = FindViewById<ImageView>(Resource.Id.imageView1);
        dragAbleBt.SetOnTouchListener(this);
        imgV1.SetOnTouchListener(this);
    }

    public override void OnWindowFocusChanged(bool hasFocus)
    {
        base.OnWindowFocusChanged(hasFocus);
        if (hasFocus)
        {
            Rect outRect = new Rect();
            this.Window.FindViewById(Window.IdAndroidContent).GetDrawingRect(outRect);
            screenWidth = outRect.Width();
            screenHeight = outRect.Height();
        }
    }
}

Please refer the source code to the github

来源：https://stackoverflow.com/questions/42489687/xamarin-imageview-drag-sample