PinchToZoomScaleDetector.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 - Nathan Barraille
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;

import com.facebook.drawee.view.SimpleDraweeView;

/**
 * A SimpleDraweeView that supports Pinch to zoom.
 */
public class PinchToZoomDraweeView extends SimpleDraweeView {
    private final ScaleGestureDetector mScaleDetector;
    private final ScaleGestureDetector.OnScaleGestureListener mScaleListener;

    private float mCurrentScale;
    private final Matrix mCurrentMatrix;
    private float mMidX;
    private float mMidY;
    @Nullable private OnZoomChangeListener mListener;

    public PinchToZoomDraweeView(Context context) {
        this(context, null);
    }

    public PinchToZoomDraweeView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PinchToZoomDraweeView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mScaleListener = new ScaleGestureDetector.SimpleOnScaleGestureListener() {
            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                float scaleFactor = detector.getScaleFactor();
                float newScale = mCurrentScale * scaleFactor;
                // Prevent from zooming out more than original
                if (newScale > 1.0f) {
                    // We initialize this lazily so that we don't have to register (and force the user
                    // to unregister) a global layout listener on the view.
                    if (mMidX == 0.0f) {
                        mMidX = getWidth() / 2.0f;
                    }
                    if (mMidY == 0.0f) {
                        mMidY = getHeight() / 2.0f;
                    }
                    mCurrentScale = newScale;
                    mCurrentMatrix.postScale(scaleFactor, scaleFactor, mMidX, mMidY);
                    invalidate();
                } else {
                    scaleFactor = 1.0f / mCurrentScale;
                    reset();
                }

                if (mListener != null && scaleFactor != 1.0f) {
                    mListener.onZoomChange(mCurrentScale);
                }

                return true;
            }
        };
        mScaleDetector = new ScaleGestureDetector(getContext(), mScaleListener);
        mCurrentMatrix = new Matrix();
    }

    public void setOnZoomChangeListener(OnZoomChangeListener listener) {
        mListener = listener;
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        setOnZoomChangeListener(null);
    }

    @Override
    protected void onDraw(@NonNull Canvas canvas) {
        int saveCount = canvas.save();
        canvas.concat(mCurrentMatrix);
        super.onDraw(canvas);
        canvas.restoreToCount(saveCount);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return mScaleDetector.onTouchEvent(event) || super.onTouchEvent(event);
    }

    /**
     * Resets the zoom on that view
     */
    public void resetZoom() {
        reset();
    }

    /**
     * Resets the zoom of the attached image.
     * This has no effect if the image has been destroyed
     */
    public void reset() {
        mCurrentMatrix.reset();
        mCurrentScale = 1.0f;
        invalidate();
    }

    /**
     * A listener interface for when the zoom scale changes
     */
    public interface OnZoomChangeListener {
        /**
         * Callback method getting triggered when the zoom scale changes.
         * This is not called when the zoom is programmatically reset
         * @param scale the new scale
         */
        public void onZoomChange(float scale);
    }
}

It will be useful if you can add a functionality to make the image move by drag. For now, it's only zooming with anchor center. Thanks anyway for the gist :)

Edit : Ok, so it is an example of how to pinch zoom drawee view. I got the solution for pinch zoom and drag image https://github.com/facebook/fresco/blob/master/samples/zoomable/src/main/java/com/facebook/samples/zoomable/ZoomableDraweeView.java if anyone want to use.

@nbarraille
Thank you for code.

@hendrawd
Please not if are going to use in commercial project.
This file provided by Facebook is for non-commercial testing and evaluation purposes only. Facebook reserves all rights not expressly granted.