Question

I am writing a program in Monodroid to capture a signature on screen, then save it to a jpg file. I can capture the signature fine, the problem comes when I try to save it to file. When the user wants to save the image, the below code runs:

 void buttonSave_Click(object sender, EventArgs e)
    {
        try
        {
            if (!m_locked)
            {

                MemoryStream stream = new MemoryStream();
                m_bitmap.Compress(Bitmap.CompressFormat.Jpeg, 100, stream);                                                                         
                byte[] byteArray = stream.GetBuffer();

                //string toSave = Convert.ToBase64String(byteArray);

                //save it to file (test);
                string path = "/mnt/sdcard/TestSig/";
                if (!Directory.Exists(path))
                    Directory.CreateDirectory(path);

                string file = path + "signature.jpg";


                FileOutputStream fo = new FileOutputStream(file);  

                fo.Write(byteArray);
            }
        }
        catch (Exception ex)
        {
            //display message
        }
    }

The ImageView that the signature is drawn onto is set up thus (in the activity’s OnCreate method):

       m_imageView = (ImageView)FindViewById(Resource.Id.imageView);

        m_imageView.SetBackgroundColor(Android.Graphics.Color.White);

        Display d = WindowManager.DefaultDisplay;

        m_dw = d.Width;
        m_dh = d.Height;
        m_bitmap = Bitmap.CreateBitmap((int)m_dw, (int)(m_dh * 0.5), Bitmap.Config.Argb8888);



        m_canvas = new Canvas(m_bitmap);
        m_paint = new Paint();
        m_paint.Color = Color.Black;
        m_imageView.SetImageBitmap(m_bitmap);


        m_imageView.SetOnTouchListener(this);

The problem is when I open the file in an image editor, all the dimensions are OK but it is completely black. It should look something like this:

By the way this seems to work OK when the png format is used. I am saving the image on an Android device but viewing it on a Windows PC.

Thanks.

Answer 1

In your setup of m_imageView, enable the drawing cache (and set it’s background colour):

m_imageView.DrawingCacheEnabled = true;
m_imageView.DrawingCacheBackgroundColor = Color.White;

Then fill the MemoryStream with the contents of the cache:

m_imageView.GetDrawingCache(false).Compress(Bitmap.CompressFormatJpeg,100, stream);

The call to .GetDrawingCache() will return a Bitmap of what you see inside m_imageView.