Xamarin Android X Y Coordinates

Question

Hi, I'm playing around for the first time with drag drop features in Xamarin. Basically, I'm trying to drag an image from one spot to the next.

In the Android activity I'm using the DispatchTouchEvent MotionEvent to get the RawX and RawY screed coordinates that are touched as the persons finger moves across the screen. In the Xamarin Forms for the screen I have an AbsoluteLayout that fills the screen and handled the Drop event.

The problem is the coordinates I get from Android don't seem to translate to coordinates on the xamarin forms, and when I to Image.TranslateTo( and give it the last coordinates from the android activity, it sends the image down and off the screen.

I then tried dividing the RawX and Y by the screen pixel density. This faired a little better. Now the image is on the screen but still far down at the bottom, nowhere near where my finger dropped the image. I'm missing some translation between the coordinates given to me by Android and the type of coordinate Xamarin forms is expecting. Here's what the DispatchTouchEventLooks like:

public override bool DispatchTouchEvent(MotionEvent ev)
{

        if (ev.Action == MotionEventActions.Move)
        {
            DisplayMetrics dispM = Application.Context.Resources.DisplayMetrics;

            MobileGlobals.XPointerPos = (ev.RawX / dispM.Density);
            MobileGlobals.YPointerPos = (ev.RawY / dispM.Density);

        }

        return base.DispatchTouchEvent(ev);
    }
}

Then in my form I do:

private void DropGestureRecognizer_Drop(object sender, DropEventArgs e)
{

        img.TranslateTo(MobileGlobals.XPointerPos, MobileGlobals.YPointerPos);


    }
}

Any tips are greatly appreciated.

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

You do not need to get Coordinates from native android, you could handle the drag and drop in Forms directly.

   public class PanContainer : ContentView  
   {  
     
       private double x, y;  
       public PanContainer()  
       {  
           var panGesture = new PanGestureRecognizer();  
     
           panGesture.PanUpdated += OnPanUpdated;  
           this.GestureRecognizers.Add(panGesture);  
       }  
     
       private void OnPanUpdated(object sender, PanUpdatedEventArgs e)  
       {  
           switch (e.StatusType)  
           {  
               case GestureStatus.Started:  
     
     
                   break;  
               case GestureStatus.Running:  
     
                   Content.TranslationX = x + e.TotalX;  
                   Content.TranslationY = y + e.TotalY;  
     
                   break;  
               case GestureStatus.Completed:  
     
                   x = Content.TranslationX;  
                   y = Content.TranslationY;  
     
     
                   break;  
           }  
       }  
   }  

With xaml layout.

   <AbsoluteLayout>  
     
     
           <local:PanContainer AbsoluteLayout.LayoutFlags="All" AbsoluteLayout.LayoutBounds="0,0,1,1" HeightRequest="100" WidthRequest="100" >  
     
               <StackLayout VerticalOptions="CenterAndExpand" HorizontalOptions="CenterAndExpand">  
                   <Image Background="red" HeightRequest="20" WidthRequest="20" />  
               </StackLayout>   
     
           </local:PanContainer>  
     
       </AbsoluteLayout>  

Best Regards,

Leon Lu

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