[mono-android] Trouble with Android.Graphics

[Jonathan Pryor]

On Nov 24, 2011, at 7:44 AM, Narcís Calvet wrote:
> Has this been fixed? I'm having problems compressing a bitmap as shown in
> the method below. DecodeStream returns null and I wonder if it's due to:

It's a bug in your code. When you write to a stream, the Position of the stream is at end-of-stream:

>        System.IO.MemoryStream stream = new System.IO.MemoryStream();
>        if (bmp.Compress(Android.Graphics.Bitmap.CompressFormat.Jpeg, 100, stream))
>        {
>          Android.Graphics.Bitmap b = Android.Graphics.BitmapFactory.DecodeStream(stream);

Notice that you don't rewind the stream, so the stream you're passing to Java is at EOF, and thus Java reads a 0-length stream, and does the only sane thing it can: return null.

Here's an Activity that Works For Me™ (though this is also tested with what should be the next release, so if this doesn't work for you...it'll be fixed in the next release ;-)

	[Activity (Label = "Scratch.Graphics", MainLauncher = true)]
	public class Activity1 : Activity
	{
		int count = 1;

		protected override void OnCreate (Bundle bundle)
		{
			base.OnCreate (bundle);

			// Set our view from the "main" layout resource
			SetContentView (Resource.Layout.Main);

			// Get our button from the layout resource,
			// and attach an event to it
			Button button = FindViewById<Button> (Resource.Id.myButton);

			button.Click += delegate {
				button.Text = string.Format ("{0} clicks!", count++); };
			
			var source = BitmapFactory.DecodeResource (Resources, Resource.Drawable.Icon);
			Log.Info ("*jonp*", "source? {0}", source != null);
			var dest = CompressToPNG (source);
			Log.Info ("*jonp*", "dest? {0}", dest != null);
		}

		private static Android.Graphics.Bitmap CompressToPNG (Android.Graphics.Bitmap bmp)
		{
			try {
				using (var stream = new System.IO.MemoryStream()) {
					if (bmp.Compress(Android.Graphics.Bitmap.CompressFormat.Jpeg, 100, stream)) {
						stream.Position = 0;
						var b = Android.Graphics.BitmapFactory.DecodeStream(stream);
						Log.Info ("*jonp*", "decoded stream? {0}", b != null);
						return (b == null) ? bmp : b;
					}
					else
						return bmp;
				}
			}
			catch (Exception e)
			{
				System.Diagnostics.Debug.WriteLine(e);
				return null;
			}
		}
	}

The output when I run this:

	I/*jonp*  (31153): source? True
	I/*jonp*  (31153): decoded stream? True
	I/*jonp*  (31153): dest? True

Notice that the "decoded stream" in CompressToPNG() is a non-null value.

 - Jon