Zoom on ImageView.

ImageViewZoomListener

package rs.webnet.locmar;

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.FloatMath;
import android.util.Log;
import android.view.Display;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.WindowManager;
import android.widget.ImageView;

public class ImageViewZoomListener implements OnTouchListener {
  private static final int NONE = 0;
	private static final int DRAG = 1;
	private static final int ZOOM = 2;
	
	private ImageView imageView;
	private Context context;
	private Matrix matrix = new Matrix();
	private Matrix savedMatrix = new Matrix();
	
	private int mode = NONE;

	private PointF start = new PointF();
	private PointF mid = new PointF();
	private float oldDist = 1f;

	private GestureDetector doubleTapGestureDetector;
	private int zoomLevel = 1;

	public ImageViewZoomListener(Context context) {
		super();
		this.context = context;
		doubleTapGestureDetector = new GestureDetector(context, new DoubleTapGesureDetector());
	}

	@Override
	public boolean onTouch(View v, MotionEvent event) {
		imageView = (ImageView) v;
		doubleTapGestureDetector.onTouchEvent(event);
		
		switch (event.getAction() & MotionEvent.ACTION_MASK) {
		case MotionEvent.ACTION_DOWN:
			savedMatrix.set(matrix);
			start.set(event.getX(), event.getY());
			Log.d("d", "ACTION_DOWN");
			mode = DRAG;
			break;
		case MotionEvent.ACTION_POINTER_DOWN:
			oldDist = spacing(event);
			Log.d("d", "oldDist=" + oldDist);
			if (oldDist > 10f) {
				savedMatrix.set(matrix);
				midPoint(mid, event);
				mode = ZOOM;
				Log.d("d", "mode=ZOOM");
			}
			break;
		case MotionEvent.ACTION_UP:
			Log.d("d", "ACTION_UP");
		case MotionEvent.ACTION_POINTER_UP:
			mode = NONE;
			Log.d("d", "ACTION_POINTER_UP");
			break;
		case MotionEvent.ACTION_MOVE:
			Log.d("d", "ACTION_MOVE");
			if (mode == DRAG) {
				matrix.set(savedMatrix);
				matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);
			} else if (mode == ZOOM) {
				float newDist = spacing(event);
				if (newDist > 10f) {
					matrix.set(savedMatrix);
					float scale = newDist / oldDist;
					Log.d("d", "Scale: " + scale);
					matrix.postScale(scale, scale, mid.x, mid.y);
				}
			}
			break;
		}

		imageView.setImageMatrix(matrix);

		return true;
	}

	/** Determine the space between the first two fingers */
	private float spacing(MotionEvent event) {
		float x = event.getX(0) - event.getX(1);
		float y = event.getY(0) - event.getY(1);
		return FloatMath.sqrt(x * x + y * y);
	}

	/** Calculate the mid point of the first two fingers */
	private void midPoint(PointF point, MotionEvent event) {
		float x = event.getX(0) + event.getX(1);
		float y = event.getY(0) + event.getY(1);
		point.set(x / 2, y / 2);
	}

//	private void dumpEvent(MotionEvent event) {
//		String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE", "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
//		StringBuilder sb = new StringBuilder();
//		int action = event.getAction();
//		int actionCode = action & MotionEvent.ACTION_MASK;
//		sb.append("event ACTION_").append(names[actionCode]);
//		if (actionCode == MotionEvent.ACTION_POINTER_DOWN || actionCode == MotionEvent.ACTION_POINTER_UP) {
//			sb.append("(pid ").append(action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
//			sb.append(")");
//		}
//		sb.append("[");
//		for (int i = 0; i < event.getPointerCount(); i++) {
//			sb.append("#").append(i);
//			sb.append("(pid ").append(event.getPointerId(i));
//			sb.append(")=").append((int) event.getX(i));
//			sb.append(",").append((int) event.getY(i));
//			if (i + 1 < event.getPointerCount())
//				sb.append(";");
//		}
//		sb.append("]");
//		Log.d("d", sb.toString());
//	}

	class DoubleTapGesureDetector extends GestureDetector.SimpleOnGestureListener {
		@Override
		public boolean onDoubleTap(MotionEvent e) {
			Log.i("Taghere..", "onDoubleTap " + imageView.getWidth());

//			WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
//			Display display = wm.getDefaultDisplay();
//			int width = display.getWidth();
//			int height = display.getHeight();

			if (zoomLevel == 1) {
				float scale = 2;
				matrix.postScale(scale, scale, mid.x, mid.y);

				imageView.setImageMatrix(matrix);
				zoomLevel++;
			} else {
				float scale = (float) 0.5;
				matrix.postScale(scale, scale, mid.x, mid.y);
				imageView.setImageMatrix(matrix);
				zoomLevel--;
			}

			Log.i("d", "width: " + imageView.getMeasuredHeight());
			return true;
		}
	}

}

main

//add to imageview
imageView.setOnTouchListener(new ImageViewZoomListener(SomeActivity.this));