Visual Studio debugger tips & tricks for .NET

Question

I've been working for years with VS's debugger, but every now and then I come across a feature I have never noticed before, and think "Damn! How could I have missed that? It's so useful!"

[Disclaimer: These tips work in VS 2005 on a C# project, no guarantees for older incarnations of VS or other languages]

Keep track of object instances

Working with multiple instances of a given class? How can you tell them apart? In pre-garbage collection programming days, it was easy to keep track of references - just look at the memory address. With .NET, you can't do that - objects can get moved around. Fortunately, the watches view lets you right-click on a watch and select 'Make Object ID'.

watches view http://img403.imageshack.us/img403/461/52518188cq3.jpg

This appends a {1#}, {2#} etc. after the instance's value, effectively giving the instance a unique label. It looks like this:

numbered instance http://img383.imageshack.us/img383/7351/11732685bl8.jpg

The label is persisted for the lifetime of that object.

Meaningful values for watched variables

By default, a watched variable's value is it's type. If you want to see its fields, you have to expand it, and this could take a long time (or even timeout!) if there are many fields or they do something complicated.

However, some predefined types show more meaningful information :

• strings show their actual contents
• lists and dictionaries show their elements count etc.

meaningful info http://img205.imageshack.us/img205/4808/37220487md1.jpg

Wouldn't it be nice to have that for my own types?

Hmm...

...some quality time with .NET Reflector shows how easily this can be accomplished with the DebuggerDisplay attribute on my custom type:

[System.Diagnostics.DebuggerDisplay("Employee: '{Name}'")] public class Employee {     public string Name { get { ... } }     ... } 

... re-run, and...

ta da! http://img60.imageshack.us/img60/926/79816018ha1.jpg

There's a lot more info on the subject here: MSDN

Break on all exceptions

... even the ones that are handled in code! I know, I'm such a n00b for not knowing about this ever since I was born, but here it goes anyway - maybe this will help someone someday:

You can force a debugged process to break into debug mode each time an exception is thrown. Ever went on a bug hunt for hours only to come across a piece of code like this?

try {     runStrangeContraption(); } catch(Exception ex) {     /* TODO: Will handle this error later */ } 

Catching all exceptions is really handy in these cases. This can be enabled from Debug > Exceptions... (Ctrl-Alt-E). Tick the boxes in the 'Thrown' column for each type of exception you need.

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Those were a few forehead-slapping moments for me. Would you care to share yours?

Answer 1

try {     // do something big } catch {     // breakpoint set here:     throw CantHappenException("something horrible happened that should never happen."); } 

How do you see the exception that was originally thrown? In a watch window, enter $exception