Adding Pinch & Zoom to PreviewView

Question

I have a CameraX PreviewView in which I want the user to be able to zoom in/out using the standard pinch gesture. I currently have a handler for the Click event attached to the PreviewView, but I also want to allow the user to zoom using the pinch gesture (if this requires me to convert the Click to using Touch I can do that). I have found the following page:

https://learn.microsoft.com/en-us/xamarin/android/app-fundamentals/touch/android-touch-walkthrough

But that seems to be overcomplicating things by adding many different gestures & creating a custom View, and sounded very inefficient for my scenario. I also found the following:

https://medium.com/androiddevelopers/display-a-camera-preview-with-previewview-86562433d86c#:~:text=Another%20common%20camera%20preview%20feature%20is,update%20the%20camera%E2%80%99s%20zoom%20ratio%20accordingly.&text=Another%20common%20camera%20preview,camera%E2%80%99s%20zoom%20ratio%20accordingly.&text=camera%20preview%20feature%20is,update%20the%20camera%E2%80%99s%20zoom

But I was having trouble understanding that, since it was written in Java & only displayed a small part of the code. I am pretty sure I will be inheriting from ScaleGestureDetector.SimpleOnScaleGestureListener to create a new class & overriding OnScale, although I am not completely sure what I will need to put in the override. What exactly do I need to do to add the scale gesture, and is there anything extra I need to do to keep the Click event as well? Thanks.

Answer 1

Hello,

What exactly do I need to do to add the scale gesture, and is there anything extra I need to do to keep the Click event as well? Thanks.

You need to set TouchListener with previewView1.SetOnTouchListener(new MyTouchListener(Application.Context)); You need to judge the guesture(click or Pinch & Zoom) by move distance.

Then, you can inherit from ScaleGestureDetector.SimpleOnScaleGestureListener to create a new class & overriding OnScale. Here is simple code.

   public class MyScaleGestureDetector : ScaleGestureDetector.SimpleOnScaleGestureListener  
       {  
           public override bool OnScale(ScaleGestureDetector detector)  
           {  
               //add your code here.  
     
               return true;  
           }  
       }  
       internal class MyTouchListener : Java.Lang.Object, View.IOnTouchListener  
       {  
          private Context context;  
           ScaleGestureDetector myScaleGestureDetector;  
           public MyTouchListener(Context context)  
           {  
               this.context = context;  
                myScaleGestureDetector = new ScaleGestureDetector(context, new MyScaleGestureDetector());  
          }  
     
          public bool OnTouch(View v, MotionEvent e)  
           {  
               float MoveDownX=0F;  
               if (e.Action==MotionEventActions.Down)  
               {                 
                   MoveDownX = e.RawX;  
               }  
              if (e.Action==MotionEventActions.Move)  
               {  
                   //execute the Pinch & Zoom  
                   myScaleGestureDetector.OnTouchEvent(e);  
               }  
               if (e.Action==MotionEventActions.Up)  
               {  
                 float tempDX=  e.RawX - MoveDownX;  
                   if (Math.Abs(tempDX)<6)  
                   {  
                       // distance is too low, execute click event.  
                         
                   }  
               }       
               return true;  
           }  
       }  

Best Regards,

Leon Lu

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