无法通过覆盖位图图像提取图形缓存

Question

我正试图在sdcard上保存一个画布。基本上我在onDraw（Canvas canvas）方法中绘制两个位图（一个在另一个之上）。但是当我保存文件时，只有最底层的Bitmap被存储。我张贴了代号为的onDraw方法在这里：

Paint paint = new Paint(); 
    paint.setColor(Color.BLACK); 

    //rectangle for the first image 
    rct = new Rect(10, 10, canvas.getWidth(), canvas.getHeight()); 

    // rectangle for the second image, the secong image is drawn where the user touches the screen 
    new_image = new RectF(touchX, touchY, touchX + secondBitmap.getWidth(), 
       touchY + secondBitmap.getHeight()); 

    //this is the bitmap that is drawn first 
    canvas.drawBitmap(firstBitmap, null, rct, paint); 

    //this is the bitmap drawn on top of the first bitmap on user touch 
    canvas.drawBitmap(secondBitmap, null, new_image, paint); 

    canvas.save(); 

保存写在MainActivity的SD卡在画布上的代码是：

Bitmap bm = canvas.getDrawingCache() // canvas in an object of the class I extended from View 
    String path = Environment.getExternalStorageDirectory() 
      .getAbsolutePath(); 
    boolean exists = (new File(path)).exists(); 

    OutputStream outStream = null; 
    File file = new File(path, "drawn_image" + ".jpg"); 

    try { 
     outStream = new FileOutputStream(file); 
     bmp.compress(Bitmap.CompressFormat.JPEG, 100, outStream); 
     outStream.flush(); 
     outStream.close(); 
     } 
    catch (FileNotFoundException e) { 
    e.printStackTrace(); 
    } 
    catch (IOException e) { 
     e.printStackTrace(); 
    } 

的问题是，只有基本的图像（firstBitmap的onDraw（）方法）保存在SDCard上，而不是整个画布（包含两个图像）。我是新来的画布...所以任何帮助将不胜感激

Answer 1

当getDrawingcache（）被称为它使视图无效，以获得完整的缓存。所以调试你的代码，并检查它是否正在浏览你的onDraw（）方法的每一行。