为什么％(Identity)扩展为空字符串? [英] Why does %(Identity) expand to an empty string?

问题描述

有人告诉我，以下代码应该创建一个文件组，其中包含元数据，说明是否只读:

I've been told that the following should create an ItemGroup of files with meta data saying whether they are read only or not:

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
         DefaultTargets="Run"
         ToolsVersion="12.0">

<Target Name="Main">
    <ItemGroup>
        <MyFiles Include="test.proj"> <!-- also tried with *.*. Using test.proj (this file) to be sure it is a file that exists -->
            <ReadOnly Condition='1 == $([MSBuild]::BitwiseAnd(1, $([System.IO.File]::GetAttributes("%(Identity)"))))'>True</ReadOnly>
        </MyFiles>
    </ItemGroup> 

</Target>

<Target Name="Run" Outputs="%(MyFiles.Identity)" DependsOnTargets="Main">
  <Message Text="%(MyFiles.Identity) Not ReadOnly" Condition="%(MyFiles.ReadOnly) != True"/>
  <Message Text="%(MyFiles.Identity) ReadOnly" Condition="%(MyFiles.ReadOnly) == True" />
</Target>

</Project>

但是，我得到以下输出(从Visual Studio 2013的开发人员命令提示符运行时):

However, I get the following output (when run from a Developer Command Prompt for Visual Studio 2013):

S:\>msbuild test.proj
Microsoft (R) Build Engine version 12.0.30723.0
[Microsoft .NET Framework, version 4.0.30319.34014]
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 30/10/2014 21:18:46.
Project "S:\test.proj" on node 1 (default targets).
S:\test.proj(9,13): error MSB4184: The expression "[System.IO.File]::GetAttributes('')" cannot be evaluated. The path is not of a legal form.
Done Building Project "S:\test.proj" (default targets) -- FAILED.


Build FAILED.

"S:\test.proj" (default target) (1) ->
(Main target) ->
  S:\test.proj(9,13): error MSB4184: The expression "[System.IO.File]::GetAttributes('')" cannot be evaluated. The path is not of a legal form.

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.01

S:\>

这行得通吗?如果是这样，我哪里出问题了?

Should this work? If so, where am I going wrong?

推荐答案

在目标中创建ItemGroup时似乎无法引用Item元数据.

It appears that you can't reference Item Metadata when creating an ItemGroup from within a target.

将脚本更改为:

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
         DefaultTargets="Run"
         ToolsVersion="12.0">

<ItemGroup>
    <MyFiles Include="test.proj" >
        <ReadOnly Condition='1 == $([MSBuild]::BitwiseAnd(1, $([System.IO.File]::GetAttributes("%(Identity)"))))'>True</ReadOnly>
    </MyFiles>
</ItemGroup> 

<Target Name="Run" Outputs="%(MyFiles.Identity)">
  <Message Text="%(MyFiles.Identity) Not ReadOnly" Condition="%(MyFiles.ReadOnly) != True"/>
  <Message Text="%(MyFiles.Identity) ReadOnly" Condition="%(MyFiles.ReadOnly) == True" />
</Target>

</Project>

将产生以下输出:

D:\temp\test>"C:\Program Files (x86)\MSBuild\12.0\Bin\msbuild.exe" test1.msbuild /t:run
Microsoft (R) Build Engine version 12.0.30723.0
[Microsoft .NET Framework, version 4.0.30319.18444]
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 10/30/2014 4:31:35 PM.
Project "D:\temp\test\test1.msbuild" on node 1 (run target(s)).
Run:
  test.proj Not ReadOnly
Done Building Project "D:\temp\test\test1.msbuild" (run target(s)).


Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:00.17

D:\temp\test>

如果在脚本运行之前确保所有项目都存在，则可以将脚本更改为此.但是，我怀疑，因为您是在目标用户未使用的目标范围内使用它.在这种情况下，您可能不得不求助于CreateItem任务.

You can change your script to this if all your items are guaranteed to exist before the script runs. However, I suspect since you are using it from within a target that they don't. In which case you might have to resort to the CreateItem task.

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