Taking Screenshot

I'm developing an application for taking screenshots in the device. In this application, we can draw anything on the screen. For this I am using Canvas, Paint and Path to do this.

I'm using this code to take screenshots:

        public void saveScreenshot() 
    {
        if (ensureSDCardAccess()) 
        {
            Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
            Canvas canvas = new Canvas(bitmap);
            onDraw(canvas);
            File file = new File(mScreenshotPath + "/" + System.currentTimeMillis() + ".jpg");
            FileOutputStream fos;
            try {
                fos = new FileOutputStream(file);
                bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
                fos.close();
            } catch (FileNotFoundException e) {
                Log.e("Panel", "FileNotFoundException", e);
            } catch (IOException e) {
                Log.e("Panel", "IOEception", e);
            }
        }
    }

    /**
     * Helper method to ensure that the given path exists.
     * TODO: check external storage state
     */
    private boolean ensureSDCardAccess() {
        File file = new File(mScreenshotPath);
        if (file.exists()) {
            return true;
        } else if (file.mkdirs()) {
            return true;
        }
        return false;
    }

However, when the following line is run:

Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);

my application closes with the following exception:

11-28 15:05:46.291: E/AndroidRuntime(8209): java.lang.IllegalArgumentException: width and height must be > 0

If I change the height and width, the screenshot is taken, but it's empty:

Why is that happening? What am I doing wrong?