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Control Class ToolTip During Debugging

You're debugging some code and you need to know the value of a string variable. You move your mouse over the variable and -- voila! -- a tooltip appears showing the value of the string.

But, when you think about that, things get complicated. After all, a string has many properties: How did Visual Studio know that the property you're interested in is the value of the string and not, for example, the string's length? And, more importantly, why don't you get that feature with your classes? When you hover the mouse over a variable pointing at one of your classes all that you get is your class' name: Distinctly unhelpful.

You can control what appears in the debugging tooltip in one of two ways. One way is to override your class' ToString method because Visual Studio defaults to calling ToString to generate the debugging message. However, using ToString to support debugging isn't necessarily an option.

For example, I often use ToString to supply the default representation of my class in my user interface (if I add a class to a dropdown list, the list will call my class' ToString method to get some text to display in the list). What I want displayed in my UI and what I want displayed when I'm debugging are often two different things.

There's a better solution for controlling what appears in the debugging tooltip: the DebuggerDisplay attribute. Just decorate your class with the DebuggerDisplay attribute and pass the attribute a string with property names from the class enclosed in curly braces (you can also surround the property names with additional text if you want).

This example will cause the debugging tooltip to display the Address and Type properties from my CustomerAddress class along with some explanatory text:

<DebuggerDisplay("Address={Address},Type={AddressType}")>
Friend Class CustomerAddress
    Public Property Address As String
    Public Property AddressType As String
End Class

Now, isn't that more informative?

Posted by Peter Vogel on 01/26/2015 at 2:20 PM


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