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前言

　　ScaleGestureDetector是实现多指操作缩放

　　GestureDetector 是实现单指追踪

　　这2个类的使用都很简单，下面的代码中有注释，另外其实也可以实现在TextView或者其他View中

代码

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.widget.ImageView;

import com.facebook.drawee.view.SimpleDraweeView;

public class ZoomableDraweeView4 extends ImageView {
    private ScaleGestureDetector mScaleGestureDetector;
    private GestureDetector mGestureDetector;
    private Matrix mCurrentMatrix;
    private float mMidX;
    private float mMidY;

    public ZoomableDraweeView4(Context context) {
        super(context);
        initScaleGestureDetector();
    }

    public ZoomableDraweeView4(Context context, AttributeSet attrs) {
        super(context, attrs);
        initScaleGestureDetector();
    }

    public ZoomableDraweeView4(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initScaleGestureDetector();
    }

    private void initScaleGestureDetector() {
        mCurrentMatrix = new Matrix();
        mScaleGestureDetector = new ScaleGestureDetector(getContext(), new ScaleGestureDetector.SimpleOnScaleGestureListener() {
            @Override
            public boolean onScaleBegin(ScaleGestureDetector detector) {
                //缩放开始
                return true;
            }

            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                float scaleFactor = detector.getScaleFactor();
                if (mMidX == 0f) {
                    //最小X轴缩放
                    mMidX = getWidth() / 2f;
                }
                if (mMidY == 0f) {
                    //最小Y轴缩放
                    mMidY = getHeight() / 2f;
                }
                mCurrentMatrix.postScale(scaleFactor, scaleFactor, mMidX, mMidY);
                //让View失效重绘
                invalidate();
                return true;
            }

            @Override
            public void onScaleEnd(ScaleGestureDetector detector) {
                //缩放结束
            }
        });

        GestureDetector.SimpleOnGestureListener gestureListener = new GestureDetector.SimpleOnGestureListener() {
            @Override
            public boolean onSingleTapConfirmed(MotionEvent e) {
                //单击确认
                return true;
            }

            @Override
            public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
                Log.e("zh", "onScroll: distanceX = " + distanceX);
                Log.e("zh", "onScroll: distanceY = " + distanceY);
                mCurrentMatrix.postTranslate(-distanceX, -distanceY);
                invalidate();
                return true;
            }
        };
        mGestureDetector = new GestureDetector(getContext(), gestureListener);
    }

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

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //这里将触摸事件转接给ScaleGestureDetector与GestureDetector
        mScaleGestureDetector.onTouchEvent(event);
        //mScaleGestureDetector.isInProgress() 如果缩放功能没有正在处理，就说明是单指操作中
        if (!mScaleGestureDetector.isInProgress()) {
            mGestureDetector.onTouchEvent(event);
        }
        return true;
    }

}