Today I have found a really useful class inside the System.Diagnostics namespace. It's called DebuggerTypeProxy and it allows you to customize how you types behave (or more precisely what data do they present) inside the debugger.

Often I have overwritten the ToString method just to get my type look nice in the debugger. A common problem is when there is some kind of collection of objects and the only thing that you see when you look at it is the all of them are of a certain type. That's because of the default implementation of the ToString method. If you overwrite it to return - say a Name property of you Client object, you immediately have it easier when it comes to finding the concrete instance on the list. Although DebuggerTypeProxy won't help in making you types more easily visible on the list, it can do so much more!

Basically DebuggerTypeProxyAttribute is just what the name suggests - a proxy. It is a kind of view that you can assign to your types and debugger will use it much like DebuggerVisualizerAttribute is used to provide a custom view over a data type.

A simplest possible example to demonstrate how to use DebuggerTypeProxyAttribute:

[DebuggerTypeProxy(typeof(MyTypeProxy))]
class MyType
{
}

class MyTypeProxy
{
    MyType type;
    public MyTypeProxy(MyType type)
    {
        this.type = type;
    }
    public string Hash
    {
        get { return type.GetHashCode().ToString(); }
    }
}

And result of the code turns this:

Into this:

It is highly unlikely the you would ever need to create a type proxy to display it's HashCode, the example demonstrates a concept and that is: exposing method calls as properties. Normally debugger won't show you values that result from a method call. You can access them manually by calling methods in the Watch Window, Quick Watch Window or even Immediate Window. Using DebuggerTypeProxy you can achieve a more debugger friendly access to those results (if you ever need them).

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