MSBuild Property Scope

问题

Once again I'm battling MSBuild. I want to have a property value defined with a root path. As part of the build, the path will get updated with version information. However, MSBuild seems to have its own scoping rules that seem completely backwards. Take this first example:

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="3.5">

  <PropertyGroup>
    <MyPath>\\server\folder</MyPath>
  </PropertyGroup>

  <Target Name="Main">
    <Message Text="In Main Before - MyPath = $(MyPath)"/>
    <CallTarget Targets="Task1" />
    <CallTarget Targets="Task2" />
    <CallTarget Targets="Task3" />
    <Message Text="In Main After - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task1">
    <PropertyGroup>
        <MyPath>$(MyPath)\version5</MyPath>
    </PropertyGroup>
    <Message Text="In Task1 - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task2">
    <Message Text="In Task2 - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task3">
    <Message Text="In Task3 - MyPath = $(MyPath)"/>
  </Target>

</Project>

Here's the output with this command line: msbuild PropertyScopeTest1.proj /target:Main

Project "C:\Temp\PropertyScopeTest1.proj" on node 1 (Main target(s)).
Main:
  In Main Before - MyPath = \\server\folder
Task1:
  In Task1 - MyPath = \\server\folder\version5
Task2:
  In Task2 - MyPath = \\server\folder\version5
Task3:
  In Task3 - MyPath = \\server\folder\version5
Main:
  In Main After - MyPath = \\server\folder
Done Building Project "C:\Temp\PropertyScopeTest1.proj" (Main target(s)).

Now, here's a slightly different version setting the MyPath variable in the Main target:

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="3.5">

  <PropertyGroup>
    <MyPath>\\server\path</MyPath>
  </PropertyGroup>

  <Target Name="Main">
    <Message Text="In Main Before - MyPath = $(MyPath)"/>
    <PropertyGroup>
        <MyPath>$(MyPath)\version5</MyPath>
    </PropertyGroup>
    <Message Text="In Main After PropertyGroup - MyPath = $(MyPath)"/>
    <CallTarget Targets="Task1" />
    <CallTarget Targets="Task2" />
    <CallTarget Targets="Task3" />
    <Message Text="In Main After - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task1">
    <Message Text="In Task1 - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task2">
    <Message Text="In Task2 - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="Task3">
    <Message Text="In Task3 - MyPath = $(MyPath)"/>
  </Target>

</Project>

Here's the output with this command line: msbuild PropertyScopeTest2.proj /target:Main

Project "C:\Temp\PropertyScopeTest2.proj" on node 1 (Main target(s)).
Main:
  In Main Before - MyPath = \\server\path
  In Main After PropertyGroup - MyPath = \\server\path\version5
Task1:
  In Task1 - MyPath = \\server\path
Task2:
  In Task2 - MyPath = \\server\path
Task3:
  In Task3 - MyPath = \\server\path
Main:
  In Main After - MyPath = \\server\path\version5
Done Building Project "C:\Temp\PropertyScopeTest2.proj" (Main target(s)).

I've looked at other links on this site that are similar, but all seem to be calling the MSBuild task from within the MSBuild project file. All I want to do is update the path and have it available everywhere in the project. Any ideas?

回答1:

Building on sll's answer, making the target that sets the new path a dependency instead of using CallTarget will yield the expected behaviour:

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="3.5">

  <PropertyGroup>
    <MyPath>\\server\folder</MyPath>
  </PropertyGroup>

  <Target Name="Main" DependsOnTargets="SetMyPathProperty">
    <Message Text="In Main Before - MyPath = $(MyPath)"/>
    <CallTarget Targets="Task1" />
    <Message Text="In Main After - MyPath = $(MyPath)"/>
  </Target>

  <Target Name="SetMyPathProperty">
    <PropertyGroup>
      <MyPath>$(MyPath)\version5</MyPath>
    </PropertyGroup>
  </Target>

  <Target Name="Task1">
    <Message Text="In Task1 - MyPath = $(MyPath)"/>
  </Target>

</Project>

Build Output:

Main:
  In Main Before - MyPath = \\server\folder\version5
Task1:
  In Task1 - MyPath = \\server\folder\version5
Main:
  In Main After - MyPath = \\server\folder\version5

Making SetMyPathProperty a dependency of Task1 instead of Main will result in identical behaviour to your PropertyScopeTest1.proj.

回答2:

This is a very interesting question which is investigated deeply with examples in following article: Scope of properties and item in an MSBuild script

Basically there are tricks with a local and global context switches across a target executions:

• One instance of the Project class is created for the script and contains all the values of the properties and items in a global context.
• When a target is executed, the global context is copied in a local context which will be used by the target.
• A the target execution end, the local context updates are merged back to the global context.
• Until a target execution is finished the local updates are not accessible to targets called using CallTarget or MSBuild tasks

来源：https://stackoverflow.com/questions/7534390/msbuild-property-scope