Is there a way to add an 'Import' to a project in a VS extension? - visual-studio-2013

Question

I want to add a new <Import> to a project when I detect that a particular type of file has been added to the project. (the <Import> adds a task to the build process that takes the file and performs work during a build).
(Detection of a file having been added to the project is done using IVsSolutionEvents.HandleItemAdded).
I currently have code that uses Microsoft.Build.Evaluation.Project to add an Import element to the project. However this is an edit to a project file on disk. If I use this code to add an Import after detecting the addition of a new item to the project I create a conflict between a change on disk (the new Import) and an in-memory change (the addition of the new file). The user is then presented with a dialog where they must choose which change to throw away.
My question is this:
Is there a way to add a new <Import> to a project via the visual studio extensibility API in such a way that the modification to the project would be "in-memory", avoiding a conflict between the addition of the new project item, and the addition of the Import?

Answer 1

For existing project types, I've found the easiest way is leveraging NuGet. You can define a NuGet package which contains the .targets file in a special build/ folder, and NuGet will automatically add the <Import> when it is added to a project within Visual Studio. It will also update the references if you upgrade the package in the future. A full example is the packaging of the Antlr4BuildTasks package, which currently uses the following .nuspec file to create the package. The key here is the section following the <!-- Build Configuration --> comment.
<?xml version="1.0" encoding="utf-8"?>
<package xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">
<metadata minClientVersion="2.7">
<id>Antlr4</id>
<version>0.0.0</version>
<authors>Sam Harwell, Terence Parr</authors>
<owners>Sam Harwell</owners>
<description>The C# target of the ANTLR 4 parser generator for Visual Studio 2010+ projects. This package supports projects targeting .NET 2.0 or newer, and built using Visual Studio 2010 or newer.</description>
<language>en-us</language>
<projectUrl>https://github.com/sharwell/antlr4cs</projectUrl>
<licenseUrl>https://raw.github.com/sharwell/antlr4cs/master/LICENSE.txt</licenseUrl>
<iconUrl>https://raw.github.com/antlr/website-antlr4/master/images/icons/antlr.png</iconUrl>
<copyright>Copyright © Sam Harwell 2014</copyright>
<releaseNotes>https://github.com/sharwell/antlr4cs/releases/v$version$</releaseNotes>
<requireLicenseAcceptance>true</requireLicenseAcceptance>
<developmentDependency>true</developmentDependency>
<tags>antlr antlr4 parsing</tags>
<title>ANTLR 4</title>
<summary>The C# target of the ANTLR 4 parser generator for Visual Studio 2010+ projects.</summary>
<dependencies>
<dependency id="Antlr4.Runtime" version="$version$" />
</dependencies>
</metadata>
<files>
<!-- Tools -->
<file src="..\tool\target\antlr4-csharp-$CSharpToolVersion$-complete.jar" target="tools"/>
<!-- Build Configuration -->
<file src="..\runtime\CSharp\Antlr4BuildTasks\bin\net40\$Configuration$\Antlr4.net40.props" target="build\Antlr4.props"/>
<file src="..\runtime\CSharp\Antlr4BuildTasks\bin\net40\$Configuration$\Antlr4.net40.targets" target="build\Antlr4.targets"/>
<file src="..\runtime\CSharp\Antlr4BuildTasks\bin\net40\$Configuration$\Antlr4BuildTasks.net40.dll" target="build"/>
</files>
</package>