Android 在imageview中在图像上绘制透明线的步骤

我制作了一个绘画应用程序，在该应用程序中，我在布局中使用ImageView来显示可以从相机或画廊拍摄的图像。我想在图像上画一条透明线，以便在绘制后可以看到图像。请帮助我

谢谢你的支持

我使用的代码使绘制线透明是：

myPaint.setAlpha(50);

我的代码是：

protected void onDraw(Canvas canvas) { 
     Toast.makeText(PaintScreen.this, "onDraw is called", Toast.LENGTH_SHORT).show();
     // myPaint.setAlpha(100); 
     canvas.drawBitmap(PaintScreen.this.localBitmap, 0,0,null); 
     //  canvas.drawPath(myPath, paintBlur); 
     canvas.drawPath(myPath, myPaint); Log.i("OnDRAWING", "REACH ON DRAW"); }


public class CustomView extends ImageView { 
      private float mX, mY; 

      public CustomView(Context context) { 
          super(context);        
          localBitmap = Bitmap.createBitmap(myBitmap.getWidth(), myBitmap.getHeight(), Config.ARGB_8888);
          myCanvas = new Canvas(localBitmap); 
          myPaint = new Paint(); setPaintForDraw(paintcolor, false, 30);                 
          setFocusable(true); 
          setFocusableInTouchMode(true); myPath = new Path(); 
      } 
}






private void setPaintForDraw(int color, boolean eraseMode, int brushSize) { 
          //myPaint.setAlpha(100); 
          myPaint.setAntiAlias(true);
          myPaint.setDither(true); 
          myPaint.setStyle(Paint.Style.STROKE); 
          myPaint.setColor(color); 
          myPaint.setStrokeCap(Paint.Cap.ROUND);        
          myPaint.setStrokeJoin(Paint.Join.ROUND); 
          myPaint.setStrokeWidth(brushSize);  
          myPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
          if (eraseMode) { 
              myPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
          } 
          else { myPaint.setXfermode(null); }

---

}

查看此线程，在这里您可以使用在图像上绘制的多个可绘制层

首先，您必须检查位图是否可变。如果不是，复制一份。下面是如何在图像上画一条线：

Bitmap copyBmp = yourBMP.copy(Bitmap.Config.ARGB_8888, true); //Copy if yourBMP is not mutable
Canvas canvas = new Canvas(copyBmp);
Paint paint = new Paint();
paint.setAlpha(50); //Put a value between 0 and 255
paint.setColor(Color.GRAY); //Put your line color
paint.setStrokeWidth(5); //Choose the width of your line
canvas.drawLine(startX, startY, stopX, stopY, paint); //Set the coordinates of the line

---

现在，如果显示copyBmp，您应该会看到在其上绘制了一条线

它的工作，但问题是，当我们移除手指并再次触摸时，透明颜色会变成深色myPaint，声明为onDraw实现的类的成员？