android自定义可缩放，移动图像裁剪框

在实际项目中，经常要制作一个简易的图像裁剪功能，即获取一张图片，并用一个遮罩层选择目标范围并截取保存的功能，如下图所示：

在此分享下该自定义视图的制作过程。

需求说明

整一个视图包含一个透明的遮罩层，一个透明带白色边框的矩形。要实现的功能是：

• 点击矩形框外围：无任何响应
• 点击矩形框内部：可随手指移动而移动
• 点击矩形框的4个顶点：可进行对角顶点坐标不变的情况下的矩形的缩放，同时边框变色

下面是实现该功能的完整源码

/**
 * Created by Farble on 2015/3/10.
 */
public class PhotoCropView extends View {
    private static final String TAG = "PhotoCropView";

    private onLocationListener locationListener;/*listen to the Rect */
    private onChangeLocationlistener changeLocationlistener;/*listening position changed */

    private int MODE;
    private static final int MODE_OUTSIDE = 0x000000aa;/*170*/
    private static final int MODE_INSIDE = 0x000000bb;/*187*/
    private static final int MODE_POINT = 0X000000cc;/*204*/
    private static final int MODE_ILLEGAL = 0X000000dd;/*221*/

    private static final int minWidth = 100;/*the minimum width of the rectangle*/
    private static final int minHeight = 200;/*the minimum height of the rectangle*/

    private static final int START_X = 200;
    private static final int START_Y = 200;

    private static final float EDGE_WIDTH = 1.8f;
    private static final int ACCURACY= 15;/*touch accuracy*/

    private int pointPosition;/*vertex of a rectangle*/

    private int sX;/*start X location*/
    private int sY;/*start Y location*/
    private int eX;/*end X location*/
    private int eY;/*end Y location*/

    private int pressX;/*X coordinate values while finger press*/
    private int pressY;/*Y coordinate values while finger press*/

    private int memonyX;/*the last time the coordinate values of X*/
    private int memonyY;/*the last time the coordinate values of Y*/

    private int coverWidth = 300;/*width of selection box*/
    private int coverHeight = 400;/*height of selection box*/

    private Paint mPaint;
    private Paint mPaintLine;
    private Bitmap mBitmapCover;
    private Bitmap mBitmapRectBlack;
    private PorterDuffXfermode xfermode;/*paint mode*/

    public PhotoCropView(Context context) {
        super(context);
        init();
    }

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

    pu