Pinch zoom for custom view

I have created my custom view and I want to apply pinch zoom for my custom view. How to do that?

This article on the Android Developers Blog covers this topic very well (scroll down to the section on GestureDetectors):

Making Sense of Multitouch

If you just want to implement pinch-to-zoom, there's only a few lines of code you'll need:

private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;

public MyCustomView(Context mContext){
    //...
    //Your view code
    //...
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}

@Override
public boolean onTouchEvent(MotionEvent ev) {
    // Let the ScaleGestureDetector inspect all events.
    mScaleDetector.onTouchEvent(ev);
    return true;
}

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    canvas.save();
    canvas.scale(mScaleFactor, mScaleFactor);
    //...
    //Your onDraw() code
    //...
    canvas.restore();
}

private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        mScaleFactor *= detector.getScaleFactor();
        
        // Don't let the object get too small or too large.
        mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));

        invalidate();
        return true;
    }
}

The rest of the article deals with handling other gestures but rather than using their implementation, you can use GestureDetector just like ScaleGestureDetector is used in the code above.

Put your view inside ZoomView.

Custom view available here https://github.com/Polidea/android-zoom-view it's easy, free and so much fun!

This library allows you to apply zooming and panning to custom views. It worked for my needs:

https://github.com/natario1/ZoomLayout

use this :

> Implementation of ImageView for Android that supports zooming, by various touch gestures.

https://github.com/chrisbanes/PhotoView