自定义可拖放缩的Android ImageView

        import android.content.Context;
        import android.graphics.Bitmap;
        import android.graphics.Color;
        import android.graphics.Matrix;
        import android.graphics.PointF;
        import android.util.AttributeSet;
        import android.view.GestureDetector;
        import android.view.GestureDetector.SimpleOnGestureListener;
        import android.view.MotionEvent;
        import android.view.View;


/**
 *
 * @ClassName:MatrixImageView
 * @author: LQF
 * @date: 2017/4/24 10:19
 * @description: 带放大、缩小、移动效果的ImageView
 */
public class MatrixImageView extends android.support.v7.widget.AppCompatImageView {
    private GestureDetector mGestureDetector;
    /** 模板Matrix，用以初始化 */
    private Matrix mMatrix = new Matrix();
    /** 图片长度 */
    private float mImageWidth;
    /** 图片高度 */
    private float mImageHeight;

    public MatrixImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        MatrixTouchListener mListener = new MatrixTouchListener();
        setOnTouchListener(mListener);
        mGestureDetector = new GestureDetector(getContext(),
                new GestureListener(mListener));
        // 背景设置为balck
        setBackgroundColor(Color.BLACK);
        // 将缩放类型设置为FIT_CENTER，表示把图片按比例扩大/缩小到View的宽度，居中显示
        setScaleType(ScaleType.FIT_CENTER);
    }

    @Override
    public void setImageBitmap(Bitmap bm) {

        super.setImageBitmap(bm);
        // 设置完图片后，获取该图片的坐标变换矩阵
        mMatrix.set(getImageMatrix());
        float[] values = new float[9];
        mMatrix.getValues(values);
        // 图片宽度为屏幕宽度除缩放倍数
        mImageWidth = getWidth() / values[Matrix.MSCALE_X];
        mImageHeight = (getHeight() - values[Matrix.MTRANS_Y] * 2)
                / values[Matrix.MSCALE_Y];
    }

    public class MatrixTouchListener implements OnTouchListener {
        /** 拖拉照片模式 */
        private static final int MODE_DRAG = 1;
        /** 放大缩小照片模式 */