How do you upgrade the *.props included in a NuGet package? - nuget

Question

I'm working on an internal NuGet package that adds a pre-build event.
It does this by specifying a build folder containing a MyPackage.props file per the documentation.
Here is the contents of the props file:
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<PropertyGroup>
<PreBuildEvent>Some commands go here</PreBuildEvent>
</PropertyGroup>
</Project>
If the project has never had a pre-build event, the event is created. However, if there is an existing PerBuildEvent element in the csproj file, the new value does not get populated. I can get it to work if I open up the csproj file and manually delete the appropriate PropertyGroupElement:
<PropertyGroup>
<PreBuildEvent>Some command line stuff</PreBuildEvent>
</PropertyGroup>
However, I have to delete if from there, as just deleting the contents of the pre-build event in the UI does not allow the new value to be written.
I want to use the convention based method over doing this in install.ps1 because the documentation specifies:
[NuGet 3.x] This script will not be executed in projects managed by project.json
...and (I left this part out before) is there a way to do this when there is no csproj file?
What's going on?

Answer 1

I would suggest you do not use a prebuild event in your .props since I would expect that you do not want to overwrite an existing one in the project.
Instead you could look at using another target so that your logic runs before the build by using the BeforeTargets:
<Target Name="MyBeforeBuild" BeforeTargets="Build">
<Message Text="### MyBeforeBuild ###" Importance="high" />
</Target>
You may also want to look at using the DependsOnTargets attribute if you need your pre-build event to run after some other target.
<Target Name="MyTarget" DependsOnTargets="$(CoreCompileDependsOn)">
</Target>