Property overwrite behaviour
- by jeremyj
I thought it worth sharing about property overwrite behaviour because i found it confusing at first in the hope of preventing some learning pain for the uninitiated with MSBuild :-)The confusion for me came because of the redundancy of using a Condition statement in a _project_ level property to test that a property has not been previously set. What i mean is that the following two statements are always identical in behaviour, regardless if the property has been supplied on the command line - <PropertyGroup> <PropA Condition=" '$(PropA)' == '' ">PropA set at project level</PropA> </PropertyGroup>has the same behaviour regardless of command line override as - <PropertyGroup>
<PropA>PropA set at project level</PropA>
</PropertyGroup>
i.e. the two above property declarations have the same result whether the property is overridden on the command line or not.To prove this experiment with the following .proj file -<?xml version="1.0" encoding="utf-8"?><Project ToolsVersion="4.0" > <PropertyGroup> <PropA Condition=" '$(PropA)' == '' ">PropA set at project level</PropA> </PropertyGroup> <Target Name="Target1"> <Message Text="PropA: $(PropA)"/> </Target> <Target Name="Target2"> <PropertyGroup> <PropA>PropA set in Target2</PropA> </PropertyGroup> <Message Text="PropA: $(PropA)"/> </Target> <Target Name="Target3"> <PropertyGroup> <PropA Condition=" '$(PropA)' == '' ">PropA set in Target3</PropA> </PropertyGroup> <Message Text="PropA: $(PropA)"/> </Target> <Target Name="Target4"> <PropertyGroup> <PropA Condition=" '$(PropA)' != '' ">PropA set in Target4</PropA> </PropertyGroup> <Message Text="PropA: $(PropA)"/> </Target></Project>Try invoking it using both of the following invocations and observe its output -1)>msbuild blog.proj /t:Target1;Target2;Target3;Target42)>msbuild blog.proj /t:Target1;Target2;Target3;Target4 "/p:PropA=PropA set on command line"Then try those two invocations with the following three variations of specifying PropA at the project level -1) <PropertyGroup>
<PropA Condition=" '$(PropA)' == '' ">PropA set at project level</PropA>
</PropertyGroup>
2)
<PropertyGroup>
<PropA>PropA set at project level</PropA>
</PropertyGroup>3) <PropertyGroup>
<PropA Condition=" '$(PropA)' != '' ">PropA set at project level</PropA>
</PropertyGroup>
