Nguyễn Ngọc Tân Nguyễn Ngọc Tân - 1 month ago 8
Android Question

How to zoom in an ImageView in Android

I am trying about zoomin or zoomout an image using ImageView, I am using Draw Canvas to draw it step by step, x2,x3 or -x2,-x3 , so that it is not efficiently and cannot move into the image spot i wanna zoomin, I dont know why. Can somebody give me new advice or new idea how to zoomin or zoomout image should be smooth. Thank you very much

Answer Source

Try this,

JAVA: package test.com;

public class TouchImageView extends ImageView {
    private Matrix matrix;
    // We can be in one of these 3 states
    private static final int NONE = 0;
    private static final int DRAG = 1;
    private static final int ZOOM = 2;
    private int mode = NONE;
    // Remember some things for zooming
    private final PointF last = new PointF();
    private final PointF start = new PointF();
    private float maxScale = 3f;
    private float[] m;
    private int viewWidth;
    private int viewHeight;
    private static final int CLICK = 3;
    private float saveScale = 1f;
    private float origWidth;
    private float origHeight;
    private int oldMeasuredHeight;
    private ScaleGestureDetector mScaleDetector;

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

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

    private void sharedConstructing(Context context) {

        super.setClickable(true);

        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);
                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;

    }

    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;
            float minScale = 1f;
            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;
        }
    }

    private 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);
    }


    private 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;

    }

    private 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;
        int 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();
    }
}

XML:

<test.com.TouchImageView
    android:id="@+id/iv_zoom"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>