Question

I have a Canvas I draw on, I’m trying to take the bitmap out, convert it to a byte array and save it serialized into a file. then later open, deserialize, and apply the bitmap back to the canvas. In the code below everything seems to work well except that when applying the bitmap to canvas nothing appears. can someone please show me where I’m going wrong.

public byte[] getCanvasData(){

    ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
    mBitmap.compress(CompressFormat.PNG, 0, bos); 
    byte[] bitmapdata = bos.toByteArray();
    return bitmapdata;
}

public void setCanvasData(byte[] canvasData, int w, int h){
    mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    mBitmap.eraseColor(0x00000000);
    mCanvas = new Canvas(mBitmap);
    mCanvas.drawBitmap(BitmapFactory.decodeByteArray(canvasData , 0,  canvasData.length).copy(Bitmap.Config.ARGB_8888, true), 0, 0, null);

}

ADDED SOME EXTRA CODE TO POSSIBLY HELP A LITTLE

public void readInSerialisable() throws IOException
{
    FileInputStream fileIn = new FileInputStream("/sdcard/theBKup.ser");

    ObjectInputStream in = new ObjectInputStream(fileIn);


    try
    { 
       BookData book = (BookData) in.readObject();
       pages.clear();
       canvasContainer.removeAllViews();

       for (int i = 0; i < book.getBook().size(); i++){
           Log.d("CREATION", "LOADING PAGE " + i);
           pages.add(new Canvas2(context, book.getPageAt(i), canvasContainer.getWidth(), canvasContainer.getHeight()));
       }

       canvasContainer.addView(pages.get(page), new AbsoluteLayout.LayoutParams(AbsoluteLayout.LayoutParams.FILL_PARENT, AbsoluteLayout.LayoutParams.FILL_PARENT, 0, 0));

       updatePagination();
       Log.d("CREATION", "Updated Pagination");
    }
    catch (Exception exc)
    {
        System.out.println("didnt work");
        exc.printStackTrace();
    }
}

BookData – Serializable class containing all my data, simple gets/sets in there

onDraw Method

 @Override
protected void onDraw(Canvas canvas) {
    Log.d("DRAWING", "WE ARE DRAWING");
    canvas.drawColor(0x00AAAAAA); //MAKE CANVAS TRANSPARENT
    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
    canvas.drawPath(mPath, mPaint);
}

Answer 1

I would do the following 2 tests.

1. Log some of the byte stream to make sure that it was loaded correctly. Something like Log.v(canvasData[0]+canvasData[1]);, or put a break point there, or something just to make sure the data is correct.
2. Draw a bitmap that you know is valid, using the same code, and see if it appears correctly.

I’m not sure exactly what’s going on, but I strongly suspect one of the following.

1. The byte stream is not being read in correctly.
2. The bitmap is not being updated to the screen, or is using a trivially small size.

In the event that your byte stream data has something, then you will want to take a look at the Canvas documentation. Specifically, look at the following bit.

In order to see a Canvas, it has to be put on to a view. Once it is on a view, the onDraw() command must be called for it to be visible. I would make sure that you are in fact doing an onDraw(), and that the Canvas is associated with the View correctly. If you are using an onDraw() already, please post the bits of code associated with it.