Tell the debugger what type to show using DebuggerTypeProxy Attribute (C#, Visual Basic, C++/CLI)

DebuggerTypeProxyAttribute specifies a proxy, or stand-in, for a type and changes the way the type is displayed in debugger windows. When you view a variable that has a proxy, the proxy stands in for the original type in the display. The debugger variable window displays only the public members of the proxy type. Private members aren't displayed.

This attribute can be applied to:

• Structures
• Classes
• Assemblies

Note

For native code, this attribute is supported only in C++/CLI code.

A type proxy class must have a constructor that takes an argument of the type for the proxy to replace. The debugger creates a new instance of the type proxy class every time it needs to display a variable of the target type. This can have performance implications. As a result, avoid any unnecessary work in the constructor.

To minimize performance penalties, the expression evaluator doesn't examine the attributes on the display proxy of the type unless the type is expanded by the user clicking the + symbol in the debugger window or by the use of DebuggerBrowsableAttribute. Therefore, don't place attributes on the display type itself. Attributes can and should be used in the body of the display type.

It's a good idea for the type proxy to be a private nested class within the class that the attribute targets. This allows it to access internal members easily.

DebuggerTypeProxyAttribute can be inherited, so if a type proxy is specified on a base class it applies to any derived classes, unless those derived classes specify their own type proxy.

If DebuggerTypeProxyAttribute is used at the assembly level, the Target parameter specifies the type for the proxy to replace.

For an example of how to use this attribute along with DebuggerDisplayAttribute and DebuggerTypeProxyAttribute, see Using the DebuggerDisplay Attribute.

Important

If you select the Show raw structure of objects in variables windows option, the DebuggerDisplay attribute is ignored. This setting is located in the Tools > Options pane in the All Settings > Debugging > General section.

Using Generics with DebuggerTypeProxy

Support for generics is limited. For C#, DebuggerTypeProxy supports only open types. An open type, also called an unconstructed type, is a generic type that isn't instantiated with arguments for its type parameters. Closed types, also called constructed types, aren't supported.

The syntax for an open type looks like this:

Namespace.TypeName<,>

If you use a generic type as a target in DebuggerTypeProxy, you must use this syntax. The DebuggerTypeProxy mechanism infers the type parameters for you.

For more information on open and closed types in C# see the C# Language Specification, section 20.5.2 Open and closed types.

Visual Basic doesn't have open type syntax, so you can't do the same thing in Visual Basic. Instead, you must use a string representation of the open type name.

"Namespace.TypeName'2"

Related content

• Using the DebuggerDisplay Attribute
• Create custom views of managed objects
• Enhancing Debugging with the Debugger Display Attributes