上代码，然后没了

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.os.Handler;
import android.os.Message;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.ImageView;

import com.example.culturecloud.R;

import java.util.HashMap;

/**
 * Created by leafly on 2019/12/12.
 */

public class ErasureView extends ImageView {
    private int height,width;
    private Bitmap front_Bitmap,back_Bitmap;
    private Bitmap fore_bitmap;
    String str = "";
    private Paint paint;
    private Canvas canvasTemp;//声明画布类
    Path path;//画图类
    HashMap<Integer,PointBean> points=new HashMap<Integer, PointBean>();
    private Boolean is_prepare_size = false,is_prepare_bitmap = false,is_prepare = true;

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

    public ErasureView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        paint =new Paint();
        init();
    }
    void init_paint(){
        paint.setColor(Color.RED);//设置画笔颜色
        paint.setStrokeWidth(25);//设置描边宽度
        BlurMaskFilter bmf = new BlurMaskFilter(40, BlurMaskFilter.Blur.NORMAL);//指定了一个模糊的样式和半径来处理Paint的边缘。
        paint. setMaskFilter(bmf);//为Paint分配边缘效果。
        paint.setStyle(Paint.Style.FILL);//让画出的图形是空心的
        //paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));//它的作用是用此画笔后，画笔划过的痕迹就变成透明色了。画笔设置好了后，就可以调用该画笔进行橡皮痕迹的绘制了
        paint.setStrokeJoin(Paint.Join.ROUND);//设置结合处的样子 Miter:结合处为锐角， Round:结合处为圆弧：BEVEL：结合处为直线。
        paint.setStrokeCap(Paint.Cap.ROUND);//画笔笔刷类型   方形形状
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
        path = new Path();//实例化画图类
    }

    void init_canvas() {
        int width = this.getWidth(); // 获取宽度
        int height =this.getHeight(); // 获取高度
        Bitmap bitmap = resizeBitmap(front_Bitmap,width ,height);
        fore_bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_4444);
        canvasTemp = new Canvas(fore_bitmap);
        canvasTemp.drawColor(Color.TRANSPARENT);
        canvasTemp.drawBitmap(bitmap,0,0,null);
        is_prepare = true;
    }

    public void setImages(Bitmap front_Bitmap,Bitmap back_Bitmap){
        this.front_Bitmap= front_Bitmap;
        this.setImageBitmap(back_Bitmap);
        is_prepare_bitmap = true;
        if(is_prepare_size){
            init_canvas();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if(is_prepare){
            int pointerCount = event.getPointerCount();
            HashMap<Integer,PointBean> new_points=new HashMap<Integer, PointBean>();
            int id = 0;
            long time=System.currentTimeMillis();
            if (canvasTemp != null) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        break;
                    case MotionEvent.ACTION_POINTER_DOWN:
                        break;
                    case MotionEvent.ACTION_MOVE:
                        for (int i = 0; i < pointerCount; i++) {
                            int point_id=(int) event.getPointerId(i);
                            int x = (int) event.getX(i);
                            int y = (int) event.getY(i);
                            new_points.put(point_id,new PointBean(x,y,time));
                            if(points.containsKey(point_id)) {
                                PointBean old_point=points.get(point_id);
                                if(time-old_point.mCurTime<150) canvasTemp.drawLine(old_point.x,old_point.y,x,y,paint);
                            }
                        }
                        points=new_points;
                        break;
                    case MotionEvent.ACTION_UP:
                        break;
                    case MotionEvent.ACTION_POINTER_UP:
                        break;
                }
            }
            postInvalidate();//刷新界面
        }
        return true;
    }
    private void init(){
        init_paint();
        getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                int new_width = getWidth();
                int new_height =  getHeight();
                if(new_height!=height||new_width!=width){
                    width = new_width;
                    height = new_height;
                    is_prepare_size =true;
                    if (is_prepare_bitmap){
                        init_canvas();
                    }
                }
                postInvalidate();
            }
        });
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if(is_prepare){
            canvas.drawBitmap(fore_bitmap, 0, 0, null);//绘制图像
        }
    }

    public Bitmap resizeBitmap(Bitmap bitmap,int bitmap_width,int bitmap_height){
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        float scaleWidth = (float)bitmap_width/width;
        float scaleHeight =(float)bitmap_height/height;
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);
        Bitmap newbm = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix,true);
        return newbm;
    }

    public class PointBean {
        public long mCurTime=0;
        public int x;
        public int y;

        public PointBean(int x, int y, long mCurTime)
        {
            this.x=x;
            this.y=y;
            this.mCurTime=mCurTime;
        }
    }
}