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A long while back I had written a quick sample when Silverlight introduced drag-and-drop into the framework.  Then I decided to show dragging MP3 files into a Silverlight app and reading the metadata and album art.  In order to accomplish this I had to read into the ID3 data from a Silverlight library.  I found a few libraries but settled on TagLib# to do the job.  I had to modify it a bit to get it working in Silverlight as the .NET profile wasn’t the same.  Recently a surge of people have been emailing me for the code.  I spent time searching and apparently I didn’t think the TagLib# modifications were that important because I never saved them anywhere!  A conversation started on Twitter and I decided to devote some “20% time” to making these modifications and take it a step further and make it into a Portable Class Library (PCL).  Here’s my journey…

Deciding to Fork

My first task was finding the source of truth for TagLib#.  The main link on the Novell developer site was broken and stale.  I found it on GitHub and started looking around.  It really hadn’t been updated in a long while (after all, it really didn’t need to be fore core .NET framework) and the project is very stale.  There is no open issues list on GitHub as you have to use Bugzilla, but that didn’t even look like it was getting much attention.  I emailed the maintainer listed in the authors file in the repository and he indicated he’s not really the maintainer.  This felt like a project kind of fizzling down (if not fizzled already).

In looking at the tests, the project structure, and taking into account that I may want to do some things different, I made the decision to fork rather than clone.  I’m not totally married to the decision but I don’t think anyone is keeping the lights on to take a pull request either though.  I forked the code and started with new projects and using Visual Studio 2013 as my tool of choice.

Using Shared Projects

At first I thought that I would be doing perhaps a few different flavors, portable and full .NET framework.  Because I thought I would I decided to use the new Shared Project system in Visual Studio 2013 and the new Shared Project Reference Manager VS extension that allows me to add references from any project to shared code easily.  This gives me the flexibility for the future and sets my project system up in advance.  You’ll see in the end I haven’t actually needed to take that step and perhaps won’t even need the Shared Project anymore, but for now I’m keeping it as it does me no harm.

First Compile

Once I moved the code over and set my target profile for PCL, I hit build.  Whoa.  About 140 compile errors.  Immediately I thought that I didn’t want to spend the time.  I took a look at the issues and quickly realized that the base code had, in fact, changed a bit from when I messed with it in Silverlight.  I started making a list of the things that weren’t compiling as I was targeting .NET 4.5, Silverlight 5, Windows 8+, Windows Phone 8+, and iOS/Android (Xamarin).  The biggest errors came from the fact that the library was still using XmlDocument and hadn’t moved to XLinq.  Beyond that there were things like Serializable, ICloneable, ComVisible and File IO that weren’t going to work.  I got really frustrated quickly and about gave up.

Working at Microsoft I am fortunate to have access to try more things and indeed I reached out to some folks for help.  I was able to get some things working continued with XmlDocument, but it didn’t feel right and starting to think about releasing this updated library I just realized this wasn’t going to work.  I remained frustrated.

Helpful Friends

Sometimes when you are frustrated you just want to vent to the world.  We call that Twitter these days.  I was pulling some hair out and posted a comment, which was quickly replied by a member of the .NET team with a bit of a touché comment. 

I chuckled but I also knew that David and others were going to be the key to helping me find the fastest path here.  I started emails with the PCL team, including David and Daniel, who are incredibly knowledgeable and responsive.  I finally got most working and then my colleague and I started chatting about my frustrations.  He worked on XLinq for a bit and basically told me to suck it up and do the conversions and that it wasn’t that bad.  We walked through a few of the scenarios and indeed it really ended up all being isolated into one area that I could quickly scan through.  I could now remove my dependency on XmlDocument and have no other dependencies for this portable library.

Hooray for helpful people!  Even when you vent, the good peeps will still help out!

Changes to TagLib# for portability

After the full conversion, a few things remain.  Right now I have #ifdef’d out come of the interfaces and attributes that weren’t working.  Once I get to a point of porting all the tests over, I’ll decide if they are even needed.  Perhaps the biggest change though for users of this lib will be the removal of the default string path of file access.  In discussing with some folks, I could have tried to make a portable storage layer work, but it started to make less sense quickly to do that in the library and leave that simple task to the app developer.  This provides flexibility for the app to do what they want without the library trying to work around how different platforms do their file IO routines.  What that means is that the default way of reading a file’s tags changes from:

var tagFile = File.Create("ironlionzion.mp3");
var tags = tagFile.GetTag(TagTypes.Id3v2);
string album = tags.Album;


' file is a StorageFile
var fileStream = await file.OpenStreamForReadAsync();
var tagFile = File.Create(new StreamFileAbstraction(file.Name, fileStream, fileStream));
var tags = tagFile.GetTag(TagTypes.Id3v2);
string album = tags.Album;

in a simple case.  Yes, you as the app author have to write a bit more code, but it puts you in control of ensuring the file location you are reading.  You can see here that I did add my StreamFileAbstraction class to my fork by default, which was the key in the Silverlight port and is actually the key for WinRT as well.  Any app developer can create their own IFileAbstraction implementation and substitute it in the ctor of the create functions and be ready to read.  I actually did this in the test project to re-implement a LocalFileAbstraction for test purposes and used the System.IO.File classes to achieve that, which are available when running VS unit tests.


What started out as a frustrating exercise turned out to be helpful for me to better understand PCLs and hopefully add value to those who have been asking for this.  As mentioned, this isn’t fully tested and still a ways to go, so if you use it please log bugs (and help fix them) to complete the implementation.  I won’t be working on this full time of course, but do hope to get the test suite ported over as well.  Here are some relevant links:

Hope this helps!

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I’m working on a little sample application for music management in Silverlight using WCF RIA Services and some other new Silverlight 4 features.  One thing that I wanted to add to the application was the ability to drag an audio file and either lookup the data and/or add a new album/artist/song to the library automatically.

Audio formats have a ‘tag’ format known as ID3.  It’s a format used for audio file metadata that is used in Windows Media Player, iTunes, and various hardware devices as well.  Over the years there has been an evolution of this format, with the older ID3v1 format basically taking up a header space with fixed character spaces for various things like Album, Artist, Title, Year, Track.  Over time though the ID3v2 format has been adapted more as it is more flexible for things like album art, and longer titles, etc.  There are various implementations of ID3 libraries for .NET that developers can choose from.  All of these implementations don’t take into account Silverlight unfortunately.

Silverlight can only reference Silverlight-compatible libraries.  Most of these libraries were targeted for the full .NET Framework and thus I can’t binary reference them.  Luckily most of them (except one) are Open Source so I could tinker.  I took the step of simply copying the files to a Silverlight project and recompiling.  This did not work 100% in a single task.  Most of the libraries had some form of Serialization attributes/constructors and almost all used some form of ASCII encoding for various string manipulation of byte arrays.

I settled on TagLib# as the library that was the easiest to modify for me.  I had to make the same changes I mentioned above to this library as well.  I created a new Silverlight 4 class library and compiled it as such.  One thing that TagLib# didn’t have was a stream input implementation.  Most of the libraries, in fact, assumed a local file path.  Luckily the library was written using a generic ‘File’ interface, so I just had to create my own StreamFileAbstraction.  I chose to do this within my project rather than the base library.  It was easy since the LocalFileAbstraction actually perfomed an Open on the file as it’s first task and set some public variables.  My abstraction basically just hands the stream already and ready to go.

Now, using the Silverlight 4 drop target feature, I created just a simple test harness to test my theory.  My XAML basically is this (pretty rudimentary just to test my theory):

   1: <Grid x:Name="LayoutRoot" Background="White">
   2:         <StackPanel>
   3:             <Border x:Name="DropZone" Width="700" Height="300" Background="Silver" CornerRadius="8" AllowDrop="True" Drop="DropZone_Drop">
   4:                 <TextBlock TextWrapping="Wrap" Text="drop here" FontSize="64" HorizontalAlignment="Center" VerticalAlignment="Center" Foreground="Gray"/>
   5:             </Border>
   6:             <Grid Height="255" Width="700">
   7:                 <Grid.ColumnDefinitions>
   8:                     <ColumnDefinition Width="111"/>
   9:                     <ColumnDefinition Width="*"/>
  10:                 </Grid.ColumnDefinitions>
  11:                 <Grid.RowDefinitions>
  12:                     <RowDefinition Height="Auto"/>
  13:                     <RowDefinition Height="Auto"/>
  14:                     <RowDefinition Height="Auto"/>
  15:                     <RowDefinition Height="Auto" />
  16:                     <RowDefinition Height="50*" />
  17:                 </Grid.RowDefinitions>
  18:                 <dataInput:Label Content="Artist" HorizontalAlignment="Right" VerticalAlignment="Top" FontWeight="Bold" Margin="4" />
  19:                 <dataInput:Label Content="Album" Grid.Row="1" HorizontalAlignment="Right" VerticalAlignment="Top" FontWeight="Bold" Margin="4" />
  20:                 <dataInput:Label Content="Title" Grid.Row="2" HorizontalAlignment="Right" VerticalAlignment="Top" FontWeight="Bold" Margin="4" />
  21:                 <dataInput:Label Grid.Column="1" HorizontalAlignment="Left" Name="Artist" Margin="4" />
  22:                 <dataInput:Label Grid.Column="1" Grid.Row="1" HorizontalAlignment="Left" Name="Album" Margin="4" />
  23:                 <dataInput:Label Grid.Column="1" Grid.Row="2" HorizontalAlignment="Left" VerticalAlignment="Top" Name="Title" Margin="4" />
  24:                 <Image Grid.Column="1" Grid.Row="4" Height="118" HorizontalAlignment="Left" Margin="4,2,0,0" Name="AlbumArt" Stretch="Fill" VerticalAlignment="Top" Width="118" />
  25:             </Grid>
  26:         </StackPanel>
  27:     </Grid>

Notice on the Border the AllowDrop=”True” attribute.  This tells Silverlight that the element can be used as a drop target (for a file from the file system).  The rendered UI looks like this:

Sample MP3 test UI

You may also notice the Drop attribute on the Border element that maps to the event handler DropZone_Drop.  This event handler basically gives us an event argument that represents the dropped objects on the surface (yes you can drop more than one).  The initial stub of this function looks like this:

   1: private void DropZone_Drop(object sender, DragEventArgs e)
   2: {
   3:     IDataObject drop = e.Data as IDataObject;
   5:     object data = drop.GetData(DataFormats.FileDrop);
   7:     FileInfo[] files = data as FileInfo[];
   9:     FileInfo file = files[0];
  10: }

I’m being a little verbose in the code to show each of the steps.  As you can see you get a FileInfo array and can pull items out of that.  For my sample I’m just assuming one item was dropped.  In the next steps I just need to get the Stream from the file and use my library.  Here is the full function (with a quick check to make sure it is a supported audio file):

   1: private void DropZone_Drop(object sender, DragEventArgs e)
   2: {
   3:     IDataObject drop = e.Data as IDataObject;
   5:     object data = drop.GetData(DataFormats.FileDrop);
   7:     FileInfo[] files = data as FileInfo[];
   9:     FileInfo file = files[0];
  11:     if (file.Extension.ToLower() != ".mp3" && file.Extension.ToLower() != ".wma")
  12:     {
  13:         MessageBox.Show("Must be an MP3 file");
  14:     }
  15:     else
  16:     {
  17:         Stream fileStream = file.OpenRead();
  19:         TagLib.File.IFileAbstraction fileAbstraction = new StreamFileAbstraction(fileStream, file.Name);
  21:         TagLib.File tagFile = TagLib.File.Create(fileAbstraction);
  23:         if (tagFile.Tag.TagTypes.HasFlag(TagLib.TagTypes.Id3v2))
  24:         {
  25:             Artist.Content = tagFile.Tag.FirstAlbumArtist;
  26:             Album.Content = string.IsNullOrEmpty(tagFile.Tag.Album) ? "NO ALBUM NAME" : tagFile.Tag.Album;
  27:             Title.Content = tagFile.Tag.Title;
  28:             if (tagFile.Tag.Pictures.Length > 0)
  29:             {
  30:                 IPicture pic = tagFile.Tag.Pictures[0];
  31:                 MemoryStream img = new MemoryStream(pic.Data.Data);
  32:                 BitmapImage bmp = new BitmapImage();
  33:                 bmp.SetSource(img);
  35:                 AlbumArt.Source = bmp;
  36:             }
  37:         }
  38:         else
  39:         {
  40:             MessageBox.Show("no id3v2 tag");
  41:         }
  42:     }

Once all the pieces are together you drag an audio file on the drop surface and the items will populate.  Here’s a quick video showing how it all works together.

Get Microsoft Silverlight

So this is just a start – and I’ve got only the tag reading working…didn’t bother looking at the other parts of the library so I know it isn’t fully ported for Silverlight.

What do you think?  Found a better implementation of ID3 tag reading?