Double-tap to zoom and pinch to zoom on ImageView in android

Question

I was looking for iphone like tap and pinch zooming with android ImageView. Mike Ortiz have done some excellent work on TouchImageView to detect boundaries. His code can be found here.

This code is missing only one thing, i.e., double-tap to zoom. Can anyone help add this feature to Mike Ortiz code?

Answer 1

It's old, but as no answer picked as correct, I would like to share it.

I've tweaked the TouchImageView class in this answer to support double tap for zooming in/out by implementing GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener interfaces

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.ImageView;

public class TouchImageView extends ImageView implements GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener {

    Matrix matrix;

    // We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;

    // Remember some things for zooming
    PointF last = new PointF();
    PointF start = new PointF();
    float minScale = 1f;
    float maxScale = 3f;
    float[] m;

    int viewWidth, viewHeight;
    static final int CLICK = 3;
    float saveScale = 1f;
    protected float origWidth, origHeight;
    int oldMeasuredWidth, oldMeasuredHeight;

    ScaleGestureDetector mScaleDetector;

    Context context;

    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }

    GestureDetector mGestureDetector;

    private void sharedConstructing(Context context) {
        super.setClickable(true);
        this.context = context;
        mGestureDetector = new GestureDetector(context, this);
        mGestureDetector.setOnDoubleTapListener(this);

        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        matrix = new Matrix();
        m = new float[9];
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);

        setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                mScaleDetector.onTouchEvent(event);
                mGestureDetector.onTouchEvent(event);

                PointF curr = new PointF(event.getX(), event.getY());

                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        last.set(curr);
                        start.set(last);
                        mode = DRAG;
                        break;

                    case MotionEvent.ACTION_MOVE:
                        if (mode == DRAG) {
                            float deltaX = curr.x - last.x;
                            float deltaY = curr.y - last.y;
                            float fixTransX = getFixDragTrans(deltaX, viewWidth,
                                    origWidth * saveScale);
                            float fixTransY = getFixDragTrans(deltaY, viewHeight,
                                    origHeight * saveScale);
                            matrix.postTranslate(fixTransX, fixTransY);
                            fixTrans();
                            last.set(curr.x, curr.y);
                        }
                        break;

                    case MotionEvent.ACTION_UP:
                        mode = NONE;
                        int xDiff = (int) Math.abs(curr.x - start.x);
                        int yDiff = (int) Math.abs(curr.y - start.y);
                        if (xDiff < CLICK && yDiff < CLICK)
                            performClick();
                        break;

                    case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        break;
                }

                setImageMatrix(matrix);
                invalidate();
                return true; // indicate event was handled
            }

        });
    }

    public void setMaxZoom(float x) {
        maxScale = x;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        // Double tap is detected
        Log.i("MAIN_TAG", "Double tap detected");
        float origScale = saveScale;
        float mScaleFactor;

        if (saveScale == maxScale) {
            saveScale = minScale;
            mScaleFactor = minScale / origScale;
        } else {
            saveScale = maxScale;
            mScaleFactor = maxScale / origScale;
        }

        matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2,
                viewHeight / 2);

        fixTrans();
        return false;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onDown(MotionEvent e) {
        return false;
    }

    @Override
    public void onShowPress(MotionEvent e) {

    }

    @Override
    public boolean onSingleTapUp(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
        return false;
    }

    @Override
    public void onLongPress(MotionEvent e) {

    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        return false;
    }

    private class ScaleListener extends
            ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            mode = ZOOM;
            return true;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            float mScaleFactor = detector.getScaleFactor();
            float origScale = saveScale;
            saveScale *= mScaleFactor;
            if (saveScale > maxScale) {
                saveScale = maxScale;
                mScaleFactor = maxScale / origScale;
            } else if (saveScale < minScale) {
                saveScale = minScale;
                mScaleFactor = minScale / origScale;
            }

            if (origWidth * saveScale <= viewWidth
                    || origHeight * saveScale <= viewHeight)
                matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2,
                        viewHeight / 2);
            else
                matrix.postScale(mScaleFactor, mScaleFactor,
                        detector.getFocusX(), detector.getFocusY());

            fixTrans();
            return true;
        }
    }

    void fixTrans() {
        matrix.getValues(m);
        float transX = m[Matrix.MTRANS_X];
        float transY = m[Matrix.MTRANS_Y];

        float fixTransX = getFixTrans(transX, viewWidth, origWidth * saveScale);
        float fixTransY = getFixTrans(transY, viewHeight, origHeight
                * saveScale);

        if (fixTransX != 0 || fixTransY != 0)
            matrix.postTranslate(fixTransX, fixTransY);
    }

    float getFixTrans(float trans, float viewSize, float contentSize) {
        float minTrans, maxTrans;

        if (contentSize <= viewSize) {
            minTrans = 0;
            maxTrans = viewSize - contentSize;
        } else {
            minTrans = viewSize - contentSize;
            maxTrans = 0;
        }

        if (trans < minTrans)
            return -trans + minTrans;
        if (trans > maxTrans)
            return -trans + maxTrans;
        return 0;
    }

    float getFixDragTrans(float delta, float viewSize, float contentSize) {
        if (contentSize <= viewSize) {
            return 0;
        }
        return delta;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = MeasureSpec.getSize(widthMeasureSpec);
        viewHeight = MeasureSpec.getSize(heightMeasureSpec);

        //
        // Rescales image on rotation
        //
        if (oldMeasuredHeight == viewWidth && oldMeasuredHeight == viewHeight
                || viewWidth == 0 || viewHeight == 0)
            return;
        oldMeasuredHeight = viewHeight;
        oldMeasuredWidth = viewWidth;

        if (saveScale == 1) {
            // Fit to screen.
            float scale;

            Drawable drawable = getDrawable();
            if (drawable == null || drawable.getIntrinsicWidth() == 0
                    || drawable.getIntrinsicHeight() == 0)
                return;
            int bmWidth = drawable.getIntrinsicWidth();
            int bmHeight = drawable.getIntrinsicHeight();

            Log.d("bmSize", "bmWidth: " + bmWidth + " bmHeight : " + bmHeight);

            float scaleX = (float) viewWidth / (float) bmWidth;
            float scaleY = (float) viewHeight / (float) bmHeight;
            scale = Math.min(scaleX, scaleY);
            matrix.setScale(scale, scale);

            // Center the image
            float redundantYSpace = (float) viewHeight
                    - (scale * (float) bmHeight);
            float redundantXSpace = (float) viewWidth
                    - (scale * (float) bmWidth);
            redundantYSpace /= (float) 2;
            redundantXSpace /= (float) 2;

            matrix.postTranslate(redundantXSpace, redundantYSpace);

            origWidth = viewWidth - 2 * redundantXSpace;
            origHeight = viewHeight - 2 * redundantYSpace;
            setImageMatrix(matrix);
        }
        fixTrans();
    }
}

Usage: You can replace your ImageView with TouchImageView in both XML & java

1. For XML

<?xml version="1.0" encoding="utf-8"?>
<com.example.android.myapp.TouchImageView 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/imViewedImage"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clickable="true"
    android:focusable="true" />

2. For Java

TouchImageView imViewedImage = findViewById(R.id.imViewedImage);

Answer 2

Pinch Zoom on ImageView in Android with Orientation handling

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PointF;
import android.os.Handler;
import android.util.AttributeSet;
import android.util.FloatMath;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.GestureDetector.SimpleOnGestureListener;

public class ZoomableImageView extends View {
    private static final String TAG = "ZoomableImageView";       

    private Bitmap imgBitmap = null;

    private int containerWidth;
    private int containerHeight;

    Paint background;   

    //Matrices will be used to move and zoom image
    Matrix matrix = new Matrix();
    Matrix savedMatrix = new Matrix();

    PointF start = new PointF();       

    float currentScale;
    float curX;
    float curY;

    //We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;

    //For animating stuff   
    float targetX;
    float targetY;
    float targetScale;
    float targetScaleX;
    float targetScaleY;
    float scaleChange;
    float targetRatio;
    float transitionalRatio;

    float easing = 0.2f;   
    boolean isAnimating = false;

    float scaleDampingFactor = 0.5f;

    //For pinch and zoom
    float oldDist = 1f;   
    PointF mid = new PointF();

    private Handler mHandler = new Handler();       

    float minScale;
    float maxScale = 8.0f;

    float wpRadius = 25.0f;
    float wpInnerRadius = 20.0f;

    float screenDensity;

    private GestureDetector gestureDetector;

    public static final int DEFAULT_SCALE_FIT_INSIDE = 0;
    public static final int DEFAULT_SCALE_ORIGINAL = 1;

    private int defaultScale;

    public int getDefaultScale() {
        return defaultScale;
    }

    public void setDefaultScale(int defaultScale) {
        this.defaultScale = defaultScale;
    }

    public ZoomableImageView(Context context) {
        super(context);       
        setFocusable(true);
        setFocusableInTouchMode(true);

        screenDensity = context.getResources().getDisplayMetrics().density;

        initPaints();
        gestureDetector = new GestureDetector(new MyGestureDetector());       
    }

    public ZoomableImageView(Context context, AttributeSet attrs) {
        super(context, attrs);

        screenDensity = context.getResources().getDisplayMetrics().density;       
        initPaints();
        gestureDetector = new GestureDetector(new MyGestureDetector());

        defaultScale = ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE;
    }

    private void initPaints() {
        background = new Paint();
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
        super.onSizeChanged(width, height, oldWidth, oldHeight);

        //Reset the width and height. Will draw bitmap and change
        containerWidth = width;
        containerHeight = height;

        if(imgBitmap != null) {
            int imgHeight = imgBitmap.getHeight();
            int imgWidth = imgBitmap.getWidth();

            float scale;
            int initX = 0;
            int initY = 0;           

            if(defaultScale == ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE) {               
                if(imgWidth > containerWidth) {           
                    scale = (float)containerWidth / imgWidth;           
                    float newHeight = imgHeight * scale;           
                    initY = (containerHeight - (int)newHeight)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(0, initY);
                }
                else {           
                    scale = (float)containerHeight / imgHeight;
                    float newWidth = imgWidth * scale;
                    initX = (containerWidth - (int)newWidth)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = scale;
                minScale = scale;
            }
            else {
                if(imgWidth > containerWidth) {                                   
                    initY = (containerHeight - (int)imgHeight)/2;                   
                    matrix.postTranslate(0, initY);
                }
                else {                               
                    initX = (containerWidth - (int)imgWidth)/2;                   
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = 1.0f;
                minScale = 1.0f;               
            }


            invalidate();           
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {               
        if(imgBitmap != null && canvas != null)
        {                                           
            canvas.drawBitmap(imgBitmap, matrix, background);                                                   
        }
    }

    //Checks and sets the target image x and y co-ordinates if out of bounds
    private void checkImageConstraints() {
        if(imgBitmap == null) {
            return;
        }

        float[] mvals = new float[9];
        matrix.getValues(mvals);

        currentScale = mvals[0];

        if(currentScale < minScale) {                               
            float deltaScale = minScale / currentScale;                   
            float px = containerWidth/2;
            float py = containerHeight/2;           
            matrix.postScale(deltaScale, deltaScale, px, py);
            invalidate();
        }       

        matrix.getValues(mvals);
        currentScale = mvals[0];
        curX = mvals[2];
        curY = mvals[5];

        int rangeLimitX = containerWidth - (int)(imgBitmap.getWidth() * currentScale);
        int rangeLimitY = containerHeight - (int)(imgBitmap.getHeight() * currentScale);


        boolean toMoveX = false;
        boolean toMoveY = false;   

        if(rangeLimitX < 0) {
            if(curX > 0) {
                targetX = 0;
                toMoveX = true;
            }
            else if(curX < rangeLimitX) {
                targetX = rangeLimitX;
                toMoveX = true;
            }
        }
        else {
            targetX = rangeLimitX / 2;
            toMoveX = true;
        }

        if(rangeLimitY < 0) {
            if(curY > 0) {
                targetY = 0;
                toMoveY = true;
            }
            else if(curY < rangeLimitY) {
                targetY = rangeLimitY;
                toMoveY = true;
            }
        }
        else {
            targetY = rangeLimitY / 2;
            toMoveY = true;
        }

        if(toMoveX == true || toMoveY == true) {
            if(toMoveY == false) {
                targetY = curY;
            }
            if(toMoveX == false) {
                targetX = curX;
            }           

            //Disable touch event actions
            isAnimating = true;
            //Initialize timer           
            mHandler.removeCallbacks(mUpdateImagePositionTask);
            mHandler.postDelayed(mUpdateImagePositionTask, 100);
        }
    }       


    @Override
    public boolean onTouchEvent(MotionEvent event) {       
        if(gestureDetector.onTouchEvent(event)) {
            return true;
        }

        if(isAnimating == true) {
            return true;
        }

        //Handle touch events here       
        float[] mvals = new float[9];
        switch(event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            if(isAnimating == false) {
                savedMatrix.set(matrix);
                start.set(event.getX(), event.getY());           
                mode = DRAG;               
            }
        break;

        case MotionEvent.ACTION_POINTER_DOWN:
            oldDist = spacing(event);           
            if(oldDist > 10f) {
                savedMatrix.set(matrix);
                midPoint(mid, event);
                mode = ZOOM;
            }
        break;

        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
            mode = NONE;

            matrix.getValues(mvals);
            curX = mvals[2];
            curY = mvals[5];
            currentScale = mvals[0];

            if(isAnimating == false) {                                       
                checkImageConstraints();
            }
        break;

        case MotionEvent.ACTION_MOVE:           
            if(mode == DRAG && isAnimating == false) {
                matrix.set(savedMatrix);
                float diffX = event.getX() - start.x;
                float diffY = event.getY() - start.y;

                matrix.postTranslate(diffX, diffY);

                matrix.getValues(mvals);
                curX = mvals[2];
                curY = mvals[5];
                currentScale = mvals[0];
            }
            else if(mode == ZOOM && isAnimating == false) {
                float newDist = spacing(event);               
                if(newDist > 10f) {
                    matrix.set(savedMatrix);
                    float scale = newDist / oldDist;                   
                    matrix.getValues(mvals);
                    currentScale = mvals[0];

                    if(currentScale * scale <= minScale) {
                        matrix.postScale(minScale/currentScale, minScale/currentScale, mid.x, mid.y);
                    }                   
                    else if(currentScale * scale >= maxScale) {
                        matrix.postScale(maxScale/currentScale, maxScale/currentScale, mid.x, mid.y);
                    }
                    else {
                        matrix.postScale(scale, scale, mid.x, mid.y);
                    }


                    matrix.getValues(mvals);
                    curX = mvals[2];
                    curY = mvals[5];
                    currentScale = mvals[0];                                       
                }
            }

        break;                               
        }

        //Calculate the transformations and then invalidate
        invalidate();
        return true;
    }

    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);
    }

    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);
    }

    public void setImageBitmap(Bitmap b) {       
        if(b != null) {
            imgBitmap = b;               

            containerWidth = getWidth();
            containerHeight = getHeight();

            int imgHeight = imgBitmap.getHeight();
            int imgWidth = imgBitmap.getWidth();

            float scale;
            int initX = 0;
            int initY = 0;

            matrix.reset();

            if(defaultScale == ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE) {               
                if(imgWidth > containerWidth) {           
                    scale = (float)containerWidth / imgWidth;           
                    float newHeight = imgHeight * scale;           
                    initY = (containerHeight - (int)newHeight)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(0, initY);
                }
                else {           
                    scale = (float)containerHeight / imgHeight;
                    float newWidth = imgWidth * scale;
                    initX = (containerWidth - (int)newWidth)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = scale;
                minScale = scale;
            }
            else {
                if(imgWidth > containerWidth) {
                    initX = 0;
                    if(imgHeight > containerHeight) {                       
                        initY = 0;
                    }
                    else {                       
                        initY = (containerHeight - (int)imgHeight)/2;
                    }

                    matrix.postTranslate(0, initY);
                }
                else {                               
                    initX = (containerWidth - (int)imgWidth)/2;
                    if(imgHeight > containerHeight) {
                        initY = 0;
                    }
                    else {
                        initY = (containerHeight - (int)imgHeight)/2;
                    }
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = 1.0f;
                minScale = 1.0f;               
            }

            invalidate();           
        }
        else {
            Log.d(TAG, "bitmap is null");
        }
    }

    public Bitmap getPhotoBitmap() {       
        return imgBitmap;
    }


    private Runnable mUpdateImagePositionTask = new Runnable() {
        public void run() {       
            float[] mvals;

            if(Math.abs(targetX - curX) < 5 && Math.abs(targetY - curY) < 5) {
                isAnimating = false;
                mHandler.removeCallbacks(mUpdateImagePositionTask);

                mvals = new float[9];
                matrix.getValues(mvals);

                currentScale = mvals[0];
                curX = mvals[2];
                curY = mvals[5];

                //Set the image parameters and invalidate display
                float diffX = (targetX - curX);
                float diffY = (targetY - curY);

                matrix.postTranslate(diffX, diffY);
            }
            else {
                isAnimating = true;
                mvals = new float[9];
                matrix.getValues(mvals);

                currentScale = mvals[0];
                curX = mvals[2];
                curY = mvals[5];

                //Set the image parameters and invalidate display
                float diffX = (targetX - curX) * 0.3f;
                float diffY = (targetY - curY) * 0.3f;

                matrix.postTranslate(diffX, diffY);               
                mHandler.postDelayed(this, 25);               
            }

            invalidate();           
        }
    };

    private Runnable mUpdateImageScale = new Runnable() {
        public void run() {           
            float transitionalRatio = targetScale / currentScale;           
            float dx;
            if(Math.abs(transitionalRatio - 1) > 0.05) {
                isAnimating = true;               
                if(targetScale > currentScale) {                                       
                    dx = transitionalRatio - 1;
                    scaleChange = 1 + dx * 0.2f;

                    currentScale *= scaleChange;

                    if(currentScale > targetScale) {
                        currentScale = currentScale / scaleChange;
                        scaleChange = 1;
                    }
                }
                else {                                   
                    dx = 1 - transitionalRatio;                   
                    scaleChange = 1 - dx * 0.5f;
                    currentScale *= scaleChange;

                    if(currentScale < targetScale) {
                        currentScale = currentScale / scaleChange;
                        scaleChange = 1;
                    }
                }


                if(scaleChange != 1) {
                    matrix.postScale(scaleChange, scaleChange, targetScaleX, targetScaleY);               
                    mHandler.postDelayed(mUpdateImageScale, 15);
                    invalidate();
                }
                else {
                    isAnimating = false;
                    scaleChange = 1;                   
                    matrix.postScale(targetScale/currentScale, targetScale/currentScale, targetScaleX, targetScaleY);
                    currentScale = targetScale;
                    mHandler.removeCallbacks(mUpdateImageScale);
                    invalidate();
                    checkImageConstraints();
                }               
            }
            else {
                isAnimating = false;
                scaleChange = 1;               
                matrix.postScale(targetScale/currentScale, targetScale/currentScale, targetScaleX, targetScaleY);
                currentScale = targetScale;
                mHandler.removeCallbacks(mUpdateImageScale);
                invalidate();
                checkImageConstraints();
            }                               
        }
    };

   /** Show an event in the LogCat view, for debugging */
   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("]");
   }

   class MyGestureDetector extends SimpleOnGestureListener {
        @Override
        public boolean onDoubleTap(MotionEvent event) {           
            if(isAnimating == true) {
                return true;
            }

            scaleChange = 1;
            isAnimating = true;
            targetScaleX = event.getX();
            targetScaleY = event.getY();

            if(Math.abs(currentScale - maxScale) > 0.1) {           
                targetScale = maxScale;
            }
            else {
                targetScale = minScale;
            }
            targetRatio = targetScale / currentScale;
            mHandler.removeCallbacks(mUpdateImageScale);
            mHandler.post(mUpdateImageScale);           
            return true;
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            return super.onFling(e1, e2, velocityX, velocityY);
        }

        @Override
        public boolean onDown(MotionEvent e) {
            return false;
        }
    }
}