Reduce the size of your XAP/APPX package: time to take out the trash!

Works on my machineUpdated on 20/02/2013

Before you even continue reading this article, I must just address a small warning: the following information has passed the WOMM certification, and as such, this works on my machine…

Recently, while browsing StackOverflow as I normally do, I found a question that really caught my attention:

Visual Studio packs into WP8 XAP unnecessary XML doc files

If you create Windows Phone 8 App in Visual Studio and reference any libs with XML documentation files supplied from nuget or manually, Visual Studio will automatically pack those XML files into output XAP as well.

In our case this weird behavior of Visual Studio increases XAP size almost twice. (We have 8Mb of xml docs in total.)

There is no such problem for WP7 app projects.

After reading this, I had to confirm this behavior myself! Here’s what I did:

  • Created a blank solution
  • Added two Windows Phone projects, one with the 7.1 SDK and the other with the 8.0.
  • Used NuGet to add Json.net package to both projects
  • Build the solution

These are the XAP files resulting from building each project:

Windows Phone XAP files from both projects

As you can see here, the WP8 version is about 60Kb larger than the WP7 version. That’s 42% larger!!!

Here is the content of the WP7 XAP file:

Windows Phone 7 XAP contents

And this is the content of the WP8 XAP file:

Windows Phone 8 XAP contents

If you look closely on the WP8 version above, you’ll see a Newtonsoft.Json.xml file – that’s the Json.net Xml Documentation!

What is it doing there? Nothing. Can we safely remove it? Most definitely, yes!

My research on why this only happens in Windows Phone 8 lead to the MSBuild process, specifically the ResolveAssemblyReferences task on Microsoft.Common.targets file: this particular task returns a variable called ReferenceCopyLocalPaths, referring to “Paths to files that should be copied to the local directory.” which upon inspection, proved to have our “garbage files”!

To fix this, edit the *.csproj files for your projects that have package outputs (XAP or APPX), and add this to the end of the file, just before the </Project> closing tag:

<PropertyGroup>
  <FilesToXapDependsOn>$(FilesToXapDependsOn);BeforeFilesToXap</FilesToXapDependsOn>
</PropertyGroup>
<Target Name="BeforeFilesToXap">
  <ItemGroup>
    <FilteredPackagingOutputs Remove="@(FilteredPackagingOutputs)" Condition="'%(FilteredPackagingOutputs.OutputGroup)' == 'CopyLocalFilesOutputGroup' AND '%(FilteredPackagingOutputs.Extension)' == '.xml'"/>
  </ItemGroup>
</Target>

This custom target will run just before the FilesToXap target, telling MSBuild to remove all XML Documentation files from the list of files to copy.

So far this has proven to work perfectly for my applications, and when I applied it to my WP8 test project, I managed to get a much more reasonable 174KB XAP file!

One final note: although this article focus on Windows Phone, I actually found out that Windows Store Apps are also affected by this issue, and that the same solution can be used to fix the problem!

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