Custom Task getting called more than once - msbuild

Question

I am learning how to use MSBuild recently so I decided to tackle writing my own custom MSBuild task. What I found is that MSBuild is calling my task just fine... but it calls it over and over and over again. It repeats the call to it many times, even though the msbuild project calls it only once.
Here is my project XML:
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0"
xmlns="http://schemas.microsoft.com/developer/msbuild/2003" >
<PropertyGroup>
<BuildDir>build directory specified here</BuildDir>
.. various other stuff here too
</PropertyGroup>
<Import Project="file1.xml" />
<Import Project="file2.xml" />
<UsingTask TaskName="CopyToBuild.Copy_To_Build"
AssemblyFile="CopyToBuild.dll" />
<Target Name="MyNewCopyTask">
<Copy_To_Build SourceFiles="#(copy_to_build)"
DestinationFolder="%(Destination)"
SkipUnchangedFiles="true"
BuildDirectory="$(BuildDir)" />
</Target>
</Project>
So as you can see I call my Copy_To_Build task only once in the project. I import an xml file that contains items that is passed in to the SourceFiles attribute of my Copy_To_Build task. Everything works great. Except for one thing: the problem is that my Execute method on my custom task gets called more than once.
public class Copy_To_Build : Microsoft.Build.Utilities.Task
{
[Required]
public ITaskItem[] SourceFiles { get; set; }
[Required]
public ITaskItem[] DestinationFolder { get; set; }
public String BuildDirectory { get; set; }
public bool Clean { get; set; }
public bool SkipUnchangedFiles { get; set; }
public override bool Execute()
{
Console.WriteLine("Build Directory: {0}", BuildDirectory);
...
}
}
I know it's getting called more than once because I put a print statement in there which reveals that the function is getting more than once. I expected it to get called only once.
Is it getting called more than once because I have some sort of threading option set? I put in a statement to print the current thread:
Console.WriteLine("Current Thread: {0}", System.Threading.Thread.CurrentThread.ManagedThreadId);
But that revealed that everything was on the same thread.
Last but not least, here is the command line script I am using to call everything:
#echo off
call "%VS100COMNTOOLS%..\..\VC\vcvarsall.bat" x64
rem set some build properties
set MISC=/nologo /verbosity:Normal
set LOGGING=/fileLogger /fileloggerparameters:LogFile=msbuild_foo.log;Encoding=UTF-8;Verbosity=Normal
set PROPERTY=/property:Platform=x64;Configuration=DebugUnicode;BuildDir=E:\foo
set TARGET=/target:MyNewCopyTask
msbuild %MISC% %LOGGING% %PROPERTY% %TARGET% foo.xml
pause
#echo on
So in summary: Why is my task getting called more than once?
Thanks

Answer 1

<Copy_To_Build SourceFiles="#(copy_to_build)"
DestinationFolder="%(Destination)"
SkipUnchangedFiles="true"
BuildDirectory="$(BuildDir)" />
It will be called once per unique value of the "Destination" metadata. This is called 'batching'. You could either do it like the way it is working right now, or make DestinationFolder property optional, and in case it is not specified, then the task can look for the "Destination" metadata in the items "SourceFiles" and copy the item to that folder.
But the usual way to do it as you have right now, just make DestinationFolder a string.