Pinch-zoomable Android frame layout -- modified to center the zoom based on the user's gesture

ZoomLayout.java

package au.id.alexn;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.FrameLayout;

/**
 * Layout that provides pinch-zooming of content. This view should have exactly one child
 * view containing the content.
 */
public class ZoomLayout extends FrameLayout implements ScaleGestureDetector.OnScaleGestureListener {

  private enum Mode {
    NONE,
    DRAG,
    ZOOM
  }

  private static final String TAG = "ZoomLayout";
  private static final float MIN_ZOOM = 1.0f;
  private static final float MAX_ZOOM = 4.0f;

  private Mode mode = Mode.NONE;
  private float scale = 1.0f;
  private float lastScaleFactor = 0f;

  // Where the finger first  touches the screen
  private float startX = 0f;
  private float startY = 0f;

  // How much to translate the canvas
  private float dx = 0f;
  private float dy = 0f;
  private float prevDx = 0f;
  private float prevDy = 0f;

  public ZoomLayout(Context context) {
    super(context);
    init(context);
  }

  public ZoomLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    init(context);
  }

  public ZoomLayout(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    init(context);
  }

  private void init(Context context) {
    final ScaleGestureDetector scaleDetector = new ScaleGestureDetector(context, this);
    this.setOnTouchListener(new View.OnTouchListener() {
      @Override
      public boolean onTouch(View view, MotionEvent motionEvent) {
        switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
          case MotionEvent.ACTION_DOWN:
            Log.i(TAG, "DOWN");
            if (scale > MIN_ZOOM) {
              mode = Mode.DRAG;
              startX = motionEvent.getX() - prevDx;
              startY = motionEvent.getY() - prevDy;
            }
            break;
          case MotionEvent.ACTION_MOVE:
            if (mode == Mode.DRAG) {
              dx = motionEvent.getX() - startX;
              dy = motionEvent.getY() - startY;
            }
            break;
          case MotionEvent.ACTION_POINTER_DOWN:
            mode = Mode.ZOOM;
            break;
          case MotionEvent.ACTION_POINTER_UP:
            mode = Mode.NONE; // changed from DRAG, was messing up zoom
            break;
          case MotionEvent.ACTION_UP:
            Log.i(TAG, "UP");
            mode = Mode.NONE;
            prevDx = dx;
            prevDy = dy;
            break;
        }
        scaleDetector.onTouchEvent(motionEvent);

        if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
          getParent().requestDisallowInterceptTouchEvent(true);
          float maxDx = child().getWidth() * (scale - 1);  // adjusted for zero pivot
          float maxDy = child().getHeight() * (scale - 1);  // adjusted for zero pivot
          dx = Math.min(Math.max(dx, -maxDx), 0);  // adjusted for zero pivot
          dy = Math.min(Math.max(dy, -maxDy), 0);  // adjusted for zero pivot
          Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
            + ", max " + maxDx);
          applyScaleAndTranslation();
        }

        return true;
      }
    });
  }

  // ScaleGestureDetector

  @Override
  public boolean onScaleBegin(ScaleGestureDetector scaleDetector) {
    Log.i(TAG, "onScaleBegin");
    return true;
  }

  @Override
  public boolean onScale(ScaleGestureDetector scaleDetector) {
    float scaleFactor = scaleDetector.getScaleFactor();
    Log.i(TAG, "onScale(), scaleFactor = " + scaleFactor);
    if (lastScaleFactor == 0 || (Math.signum(scaleFactor) == Math.signum(lastScaleFactor))) {
      float prevScale = scale;
      scale *= scaleFactor;
      scale = Math.max(MIN_ZOOM, Math.min(scale, MAX_ZOOM));
      lastScaleFactor = scaleFactor;
      float adjustedScaleFactor = scale / prevScale;
      // added logic to adjust dx and dy for pinch/zoom pivot point
      Log.d(TAG, "onScale, adjustedScaleFactor = " + adjustedScaleFactor);
      Log.d(TAG, "onScale, BEFORE dx/dy = " + dx + "/" + dy);
      float focusX = scaleDetector.getFocusX();
      float focusY = scaleDetector.getFocusY();
      Log.d(TAG, "onScale, focusX/focusy = " + focusX + "/" + focusY);
      dx += (dx - focusX) * (adjustedScaleFactor - 1);
      dy += (dy - focusY) * (adjustedScaleFactor - 1);
      Log.d(TAG, "onScale, dx/dy = " + dx + "/" + dy);
    } else {
      lastScaleFactor = 0;
    }
    return true;
  }

  @Override
  public void onScaleEnd(ScaleGestureDetector scaleDetector) {
    Log.i(TAG, "onScaleEnd");
  }

  private void applyScaleAndTranslation() {
    child().setScaleX(scale);
    child().setScaleY(scale);
    child().setPivotX(0f);  // default is to pivot at view center
    child().setPivotY(0f);  // default is to pivot at view center
    child().setTranslationX(dx);
    child().setTranslationY(dy);
  }

  private View child() {
    return getChildAt(0);
  }
}

This works perfectly on my device running Nougat (Samsung J7 Pro), but on my device running Lollipop (Samsung S4), when I zoom it moves the view to the top left position. I only have one child, here is my xml layout:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <packageName.ZoomLayout
        android:id="@+id/fZoom"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:measureAllChildren="true">

            <SurfaceView
                android:id="@+id/mSurfaceView"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                />

    </packageName.ZoomLayout>

</RelativeLayout>

I have been struggling with this for 3 days now, I can't understand how come it work on one device and not the other? Should I change something when running it on my S4?

Any advise would be greatly appreciated.

I've asked a question on stackoverflow regarding this issue - https://stackoverflow.com/q/50411590/8199772

I have used this code, Zoom is not working smoothly in Samsung Galaxy J5(2016). OS is 7.1.1 Could you please replay how can I resolve it. @HBiSoft

@jishnu02180 What view are you using inside the ZoomLayout?

Hello sir,
If i remove that code LastScaleFactor i noticed that there is no effect on code functionality is there any reason why it is needed.