降序排序非常小的数字(Descending order sort for very small numbers)

 这个功能内置在MsBuild for .Net项目中（在Microsoft.Common.Targets中搜索PostBuildEvent，也可以在这里看到），这里是一个简化版本。 原则是在构建之前获取输出文件的时间戳，在构建之后获取另一个时间戳，然后比较它们。 如果它们是相同的，显然没有真正构建。 这个逻辑有一个可能的插入点的镜像，在这里我只选择了链接阶段应该做得很好： 
 
<Target Name="GetTimeStampBeforeLink" BeforeTargets="Link">
  <ItemGroup>
    <ProjectOutputFiles Include="$(TargetPath)" />
  </ItemGroup>
  <PropertyGroup>
    <OutputTimeStampBeforeLink>%(ProjectOutputFiles.ModifiedTime)</OutputTimeStampBeforeLink>
  </PropertyGroup>
</Target>

<Target Name="GetTimeStampAfterLink" AfterTargets="Link">
  <PropertyGroup>
    <OutputTimeStampAfterLink>%(ProjectOutputFiles.ModifiedTime)</OutputTimeStampAfterLink>
    <OutputFilesModified Condition="'$(OutputTimeStampBeforeLink)' != '$(OutputTimeStampAfterLink)'">True</OutputFilesModified>
  </PropertyGroup>
</Target>
 
 您可以将此代码直接插入到项目文件中，但更好的方法是将其保存在单独的文件中，以便您可以通过将其导入到任何您想要的位置来重复使用if。 您还可以通过添加到ProjectOutputFiles ItemGroup来添加要检查的ProjectOutputFiles 。 
 
 现在剩下的就是禁用PostBuildEvent。 MsBuild已经有了一个机制，因为postbuild事件调用是以一个名为PostBuildEventUseInBuild属性为条件的，所以如果没有修改输出文件，我们将其设置为false： 
 
<Target Name="DisablePostBuildEvent" AfterTargets="GetTimeStampAfterLink">
  <PropertyGroup>
    <PostBuildEventUseInBuild Condition='"$(OutputFilesModified)' != 'True'">false</PostBuildEventUseInBuild>
  </PropertyGroup>
</Target>

This functionality is built-in in MsBuild for .Net projects (search for PostBuildEvent in Microsoft.Common.Targets, also see here), here is a simplified version. The principle is you get a timestamp of your output file(s) before the build, and another one after the build, then compare them. If they are the same, obviously nothing was really built. There's a miriad of possible insertion points for this logic, here I just picked the link stage which should do just fine:
 
<Target Name="GetTimeStampBeforeLink" BeforeTargets="Link">
  <ItemGroup>
    <ProjectOutputFiles Include="$(TargetPath)" />
  </ItemGroup>
  <PropertyGroup>
    <OutputTimeStampBeforeLink>%(ProjectOutputFiles.ModifiedTime)</OutputTimeStampBeforeLink>
  </PropertyGroup>
</Target>

<Target Name="GetTimeStampAfterLink" AfterTargets="Link">
  <PropertyGroup>
    <OutputTimeStampAfterLink>%(ProjectOutputFiles.ModifiedTime)</OutputTimeStampAfterLink>
    <OutputFilesModified Condition="'$(OutputTimeStampBeforeLink)' != '$(OutputTimeStampAfterLink)'">True</OutputFilesModified>
  </PropertyGroup>
</Target>
 
You can insert this code right into your projectfile, but a better idea is to save it in a seperate file so you can reuse if for other projects by importing it wherever you want it. Also you can add files to check by adding to the ProjectOutputFiles ItemGroup.
 
Now all is left is disabling the PostBuildEvent. MsBuild already has a mechanism for that since postbuild event invokation is conditional on a propery named PostBuildEventUseInBuild, so we set this to false if output files are not modified:
 
<Target Name="DisablePostBuildEvent" AfterTargets="GetTimeStampAfterLink">
  <PropertyGroup>
    <PostBuildEventUseInBuild Condition='"$(OutputFilesModified)' != 'True'">false</PostBuildEventUseInBuild>
  </PropertyGroup>
</Target>