How do I “run until this variable changes” when debugging?

Question

When debugging my C#, I often want to know when a variable's value changes and then investigate the state of the program.

Currently, I do it like this:

1. Watch-list the offending variable.
2. Physically spam F10 (shortcut for Step Over) until I see the value change.

However, the number of F10s required is annoying.

Surely this has been automated, I thought. But I cannot find this feature in my Microsoft Visual C# Express, which surprises me. After all, the Watch-list does automatically highlight changed values in bright red.

Am I missing something?

Answer 1

Simple trick for Express edition:

private string myValue;
public string MyValue
{
  set
  {
    if (this.myValue != value) Debugger.Break();
    this.myValue = value;
  }
}

Answer 2

Conditional breakpoints are what you're after, but it appears they are not available in Visual Studio Express.

In Visual Studio (non-Express), the way it works is that you create a conditional breakpoint with an expression equal to your watch value and "Has changed" as your breakpoint condition.

Answer 3

Here's how I do it in Visual Studio. Set a breakpoint by pressing F9 or clicking in the very left margin. Then right click over the red dot that appears and select the Condition command. There are other options there as well.

However, this may not be supported in Visual Studio Express.

Answer 4

you can use conditional breakpoints

see this

Answer 5

You could write an if statement that checks for a change and have a break point happen within that if statement, thus it breaks initially, then you click resume, it continues until it hits this break point.

Answer 6

Use Debugger.Break based on some runtime condition, or go rightclick on some breakpoint, and choose conditional break -> has changed

Edit: dunno about this in Express

Answer 7

1. Set the breakpoint where you want the code to pause
2. Open the Breakpoints window (Debug -> Windows -> Breakpoints)
3. Right-click on your breakpoint and select Condition...
4. Set the condition to be the variable name, and select the Has Changed radio button.
5. Click OK, and then debug as per normal :)

Answer 8

If you want to catch variable change at some breakpoint, as opposed to catching exactly where it was changed, then set the breakpoint, right-click it and choose "Condition". Let's say your variable name is X and it's current value is A. Enter "X != A" in the condition field.

Now the breakpoint will only be hit after X changes to some value other than A.