Android ImageView Zoom-in and Zoom-Out

Question

I want to Zoom-in and Zoom-out an Android ImageView. I tried most of the samples but in all of them the image in the ImageView itself is getting Zoomed-in and Zoomed-out, wh

Answer 1

Here is my solution, it is based on @alexbirkett's solution.

public class ZoomImageView extends ImageView {

// region . Static fields .

static final int NONE = 0;
static final int DRAG = 1;
static final int ZOOM = 2;
static final int CLICK = 3;

// endregion . Static fields .

// region . Fields .

private int mode = NONE;

private Matrix mMatrix = new Matrix();

private PointF mLastTouch = new PointF();
private PointF mStartTouch = new PointF();
private float minScale = 0.5f;
private float maxScale = 4f;
private float[] mCriticPoints;

private float mScale = 1f;
private float mRight;
private float mBottom;
private float mOriginalBitmapWidth;
private float mOriginalBitmapHeight;

private ScaleGestureDetector mScaleDetector;

//endregion . Fields .

// region . Ctor .
public ZoomImageView(Context context) {
    super(context);
    init(context);
}

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

public ZoomImageView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init(context);
}

// endregion . Ctor .

// region . Overrider .

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    int bmHeight = getBmHeight();
    int bmWidth = getBmWidth();

    float width = getMeasuredWidth();
    float height = getMeasuredHeight();
    float scale = 1;

    // If image is bigger then display fit it to screen.
    if (width < bmWidth || height < bmHeight) {
        scale = width > height ? height / bmHeight : width / bmWidth;
    }

    mMatrix.setScale(scale, scale);
    mScale = 1f;

    mOriginalBitmapWidth = scale * bmWidth;
    mOriginalBitmapHeight = scale * bmHeight;

    // Center the image
    float redundantYSpace = (height - mOriginalBitmapHeight);
    float redundantXSpace = (width - mOriginalBitmapWidth);

    mMatrix.postTranslate(redundantXSpace / 2, redundantYSpace / 2);

    setImageMatrix(mMatrix);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    mScaleDetector.onTouchEvent(event);

    mMatrix.getValues(mCriticPoints);
    float translateX = mCriticPoints[Matrix.MTRANS_X];
    float trnslateY = mCriticPoints[Matrix.MTRANS_Y];
    PointF currentPoint = new PointF(event.getX(), event.getY());

    switch (event.getAction()) {
        //when one finger is touching
        //set the mode to DRAG
        case MotionEvent.ACTION_DOWN:
            mLastTouch.set(event.getX(), event.getY());
            mStartTouch.set(mLastTouch);
            mode = DRAG;
            break;
        //when two fingers are touching
        //set the mode to ZOOM
        case MotionEvent.ACTION_POINTER_DOWN:
            mLastTouch.set(event.getX(), event.getY());
            mStartTouch.set(mLastTouch);
            mode = ZOOM;
            break;
        //when a finger moves
        //If mode is applicable move image
        case MotionEvent.ACTION_MOVE:

            //if the mode is ZOOM or
            //if the mode is DRAG and already zoomed
            if (mode == ZOOM || (mode == DRAG && mScale > minScale)) {

                // region . Move  image.

                float deltaX = currentPoint.x - mLastTouch.x;// x difference
                float deltaY = currentPoint.y - mLastTouch.y;// y difference
                float scaleWidth = Math.round(mOriginalBitmapWidth * mScale);// width after applying current scale
                float scaleHeight = Math.round(mOriginalBitmapHeight * mScale);// height after applying current scale

                // Move image to lef or right if its width is bigger than display width
                if (scaleWidth > getWidth()) {
                    if (translateX + deltaX > 0) {
                        deltaX = -translateX;
                    } else if (translateX + deltaX < -mRight) {
                        deltaX = -(translateX + mRight);
                    }
                } else {
                    deltaX = 0;
                }
                // Move image to up or bottom if its height is bigger than display height
                if (scaleHeight > getHeight()) {
                    if (trnslateY + deltaY > 0) {
                        deltaY = -trnslateY;
                    } else if (trnslateY + deltaY < -mBottom) {
                        deltaY = -(trnslateY + mBottom);
                    }
                } else {
                    deltaY = 0;
                }

                //move the image with the matrix
                mMatrix.postTranslate(deltaX, deltaY);
                //set the last touch location to the current
                mLastTouch.set(currentPoint.x, currentPoint.y);

                // endregion . Move image .
            }
            break;
        //first finger is lifted
        case MotionEvent.ACTION_UP:
            mode = NONE;
            int xDiff = (int) Math.abs(currentPoint.x - mStartTouch.x);
            int yDiff = (int) Math.abs(currentPoint.y - mStartTouch.y);
            if (xDiff < CLICK && yDiff < CLICK)
                performClick();
            break;
        // second finger is lifted
        case MotionEvent.ACTION_POINTER_UP:
            mode = NONE;
            break;
    }
    setImageMatrix(mMatrix);
    invalidate();
    return true;
}

//endregion . Overrides .

// region . Privates .

private void init(Context context) {
    super.setClickable(true);
    mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
    mCriticPoints = new float[9];
    setImageMatrix(mMatrix);
    setScaleType(ScaleType.MATRIX);
}

private int getBmWidth() {
    Drawable drawable = getDrawable();
    if (drawable != null) {
        return drawable.getIntrinsicWidth();
    }
    return 0;
}

private int getBmHeight() {
    Drawable drawable = getDrawable();
    if (drawable != null) {
        return drawable.getIntrinsicHeight();
    }
    return 0;
}

//endregion . Privates .

// region . Internal classes .

private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        mode = ZOOM;
        return true;
    }

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        float scaleFactor = detector.getScaleFactor();
        float newScale = mScale * scaleFactor;
        if (newScale < maxScale && newScale > minScale) {
            mScale = newScale;
            float width = getWidth();
            float height = getHeight();
            mRight = (mOriginalBitmapWidth * mScale) - width;
            mBottom = (mOriginalBitmapHeight * mScale) - height;

            float scaledBitmapWidth = mOriginalBitmapWidth * mScale;
            float scaledBitmapHeight = mOriginalBitmapHeight * mScale;

            if (scaledBitmapWidth <= width || scaledBitmapHeight <= height) {
                mMatrix.postScale(scaleFactor, scaleFactor, width / 2, height / 2);
            } else {
                mMatrix.postScale(scaleFactor, scaleFactor, detector.getFocusX(), detector.getFocusY());
            }
        }
        return true;
    }
}

// endregion . Internal classes .
}