Disposing of checkin policy

Recently while I was fixing up StyleCop checkin policy, I came across one small not-so-obvious snippet of knowledge worthwhile to share.

Any custom checkin policy inherits from PolicyBase, which in turn implements IDisposable. Meaning – if you need to clean up after yourself in your custom policy, Dispose method is the place for that.

So in StyleCop policy, I do a lot of Visual Studio related stuff and thus I thought I’d dispose of VS extensibility objects in Dispose method.

And here where non-obvious stuff starts. The policy is loaded in either of those cases:

• Project Source Control configuration (through menu Team->Team Project Settings->Source Control)
• Right-clicking in Solution Explorer and invoking “Check In…” menu
• Invoking “View Pending Changes” toolwindow

While the first case is not very interesting (no pending changes will be evaluated in configuration), two other cases are important.

In case of “Check In …”, “Check In” modal window is displayed (the policy is loaded), and when window is closed, custom policy class is unloaded and Dispose called. However, in case of “View Pending Changes” toolwindow the policy is loaded once when window is first created, and Dispose will be called only when Visual Studio is closed or TFS server connection is closed. That means you probably should not hold on any expensive resources until Dispose.