Create a Visual C# class library called MyTask that contains your custom task.

For more information, see Component Classes.

On the Project menu, click Add Reference, and select Microsoft.Build.Framework and Microsoft.Build.Utilities from the Add Reference dialog box.

Insert the following code to the class.cs file.

This example inherits from the Task helper class and uses the DateTime properties UtcNow and Ticks to generate the build number.

using System;
using Microsoft.Build.Utilities;
using Microsoft.Build.Framework;

namespace BuildNumberGenerator
{
    public class BuildNumberGenerator:Task
    {
        public override bool Execute()
        {            
            m_buildNumber = DateTime.UtcNow.Ticks.ToString();
            return true;
        }
        private string m_buildNumber;

        [Output]
        public string BuildNumber
        {
            get { return m_buildNumber; }
        }
    }
}

Build your class library to produce MyTask.dll.

Copy the built DLL to the local workspace folder that also contains the TFSBuild.proj file of your build definition.

Important Note:
You must have mapped the source control location of the TFSBuild.proj file to your local workspace before this directory structure exists on the client computer. For more information, see How to: Get the Source for Your Team Project.

If your TFSBuild.proj file was stored in the default folder in source control, the local copy of the file is located in <root>:\Local Workspace\TeamBuildTypes\MyBuildName on the client computer. Local Workspace is the local folder to which your team project is mapped, MyTeamProject is the name of your team project and MyBuildName is the name that you gave to the first build definition that is associated with this TFSBuild.proj file.

Click Start, point to All Programs, Microsoft Visual Studio 9.0, Visual Studio Tools, and then click Visual Studio 2008 Command Prompt. Open the local workspace you have mapped for the team project that contains the build type you want to customize.

For example, type the following at the command prompt.

> cd c:\MyTeamProject

Where MyTeamProject is the name of your team project.

Move to the location where the TFSBuild.proj file is stored.

For example, type the following at the command prompt.

c:\MyTeamProject>cd TeamBuildTypes\MyBuildName

Where MyBuildName is the name of the build definition.

To add the file to Team Foundation version control, type the following command.

c:\MyTeamProject\TeamBuildTypes\MyBuildName> tf add MyTask.dll

To check in your file to Team Foundation version control, type the following command.

c:\MyTeamProject\TeamBuildTypes\MyBuildName> tf checkin MyTask.dll

You can also use the Team Explorer to add your DLL to Team Foundation version control. For more information, see How to: Add a Project or Solution to Version Control.

Start Visual Studio.

Check out the TFSBuild.proj file that you want to modify from Team Foundation version control and open it in the Visual Studio XML-editor.

Add the UsingTask element to the TFSBuild.proj file immediately after the import statement.

<UsingTask 
    TaskName="BuildNumberGenerator.BuildNumberGenerator" 
    AssemblyFile="MyTask.dll"/>

To insert your task into the BuildNumberOverrideTarget target, add the following XML, enlosed within the <Target></Target> tags, to the end of the TFSBuild.proj file.

</ItemGroup>
  <Target Name = "BuildNumberOverrideTarget" >
    <BuildNumberGenerator> 
    <Output TaskParameter="BuildNumber" PropertyName="BuildNumber"/> 
    </BuildNumberGenerator> 
  </Target>
</Project>

Click File, click Save to save your changes, and then close TFSBuild.proj.

Note:
You will receive XML-schema warnings after you make these changes to the TFSBuild.proj file. You can safely ignore those warnings.

Check TFSBuild.proj back in to source control.

After you have modified the TFSBuild.proj file and saved the changes in Team Foundation version control, run the build definition.

For more information, see How to: Queue or Start a Build Definition.

You can view the custom build number in the Build Explorer. For more information, see How to: Monitor Build Progress.