visual-studio - 为什么 `Condition` 属性对 `ItemGroup` 元素不起作用？

Question

微软 Visual Studio 2013。

两个When和 ItemGroup元素可以有Condition属性(正如我在 MSDN 中看到的)。但我得到不同的结果。

当$(CAD_Year)是 2015 年，我预计 AcRibbon将是 不是 引用我的项目:

<ItemGroup Condition= "'$(CAD_Year)' &lt; '2010'" >    
  <Reference Include="AcRibbon">
    <HintPath>$(CAD_SDK_Location)\$(Inc)\AcRibbon.dll</HintPath>
    <Private>False</Private>
  </Reference>
</ItemGroup>

但是我在解决方案浏览器中得到 Unresolved reference AcRibbon总是。

但是这个变体工作正常:

<Choose>
  <When Condition= "'$(CAD_Year)' &lt; '2010'">
    <ItemGroup>
      <Reference Include="AcRibbon">
        <HintPath>$(CAD_SDK_Location)\$(Inc)\AcRibbon.dll</HintPath>
        <Private>False</Private>
      </Reference>
    </ItemGroup>
  </When>
</Choose>

在这种情况下， AcRibbon仅在 $(CAD_Year) 时引用低于 2010 年。
为什么我得到不同的结果？

Answer 1

我在 MSDN here 中找到了答案:

While conditional import statements work in command-line MSBuilds, they do not work with MSBuild in the Visual Studio integrated development environment (IDE). Conditional imports are evaluated by using the configuration and platform values that are set when the project is loaded. If changes are subsequently made that require a reevaluation of the conditionals in the project file, for example, changing the platform, Visual Studio reevaluates the conditions on properties and items, but not on imports. Because the import conditional is not reevaluated, the import is skipped. To work around this, put conditional imports in the .targets files or put code in a conditional block such as a Choose Element (MSBuild) block.

我认为 ItemGroup 是这样的。元素也...