C# : Exception Handling - Locating the error

Question

I have this code:

private void btnNext_Click(object sender, RoutedEventArgs e){
  try
      {
         // Lots of codes in here
      }

  catch (Exception ex)
      {
        System.Windows.MessageBox.Show(ex.Message + Environment.NewLine + ex.StackTrace.ToString()) 
      }
  finally
      {}
}

It is catching an exception but not telling me where the exception is occurring inside the code. The only thing I'm getting is this.

   Object reference not set to an instance of an object
   at ProjectPath.btnNext_Click(Object sender, RoutedEventArgs e)

The release code works fine on a lot a machines, but on few machines, it throws this exception. I just can't figure out where on the code the exception is occurring while running on those machines. Is there a way to find the exact line where the exception is occurring? ex.StackTrace didn't get the job done.

Any help will be appreciated.

Don't catch it and run it in a debugger. It will stop where the Exception is thrown. (or better, tell your debugger to stop on caught and uncaught exceptions) — Bart Friederichs, Mar 28 '13 at 21:29
Can you run it under the debugger? If you can, then just turn on the option that makes the debugger break where the exception is thrown. (Menu: Debug|Exceptions -> Turn on "`Thrown`" for 'Common Language Runtime Exceptions') — Matthew Watson, Mar 28 '13 at 21:29
Can't run under the debugger. Cannot replicate this error in the machine where I'm coding. Only occurs on few other client machines. — Butters, Mar 28 '13 at 21:30
check if you catch somewhere and do a rethrow using throw e, this cuts the callstack. just use throw to rethrow — NickD, Mar 28 '13 at 21:31
Is this for Windows? Will one of the client's with the issue allow you access to debug the issue? — StarPilot, Mar 28 '13 at 21:59
Perhaps you need to show the code that you have running in that event based on what you have shown really doesn't show nor tell us much being that there is only one real line of code you have which is suppose to display the message.. you can also look at the `ex.` and Get InnerException as well as other things .. you need to do a little bit more debugging / thinking on your end.. `look at ex.TargetSite` it will tell you the method where the error occured — MethodMan, Mar 28 '13 at 22:22

score 2 · Accepted Answer · answered Mar 28 '13 at 21:30

2

You should ideally put separate try-catch blocks around areas where you think an exception would be thrown - instead of putting everything in the same one.

Otherwise, when you debug, it creates pdb files which - if they're present in the folder where the file is executing, you can get the line number.

That said, this error is pretty common, you have a null somewhere.

Added: Over here I'm assuming that for some reason you can't get the debugger to stop on exception, and/or can't trace it because you're deploying it to a third party or something.

answered Mar 28 '13 at 21:30

Haedrian

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Yes, can't use debugger because its a deployed solution. – Butters Mar 28 '13 at 21:35
Used separate try catch block and figured out where it was. – Butters Mar 29 '13 at 14:52

score 1 · Answer 2 · answered Jan 06 '15 at 19:14

To find the exact location -- the specific line in your source code -- it helps if you run the code in a debugger and set a breakpoint within the exception handler.

If you examine the data structure referenced as a parameter to the exception handler (ex in the example), you will find a data member named StackTrace. If the location is anywhere, it will be in here. Here, for example, is a string for an exception that I am working on right how:

at DOffice.BrMan.getLastReportRefreshed() in E:\\src\\BrMan.cs:line 5370
at DOffice.BrParms.lookupParmByParmName(String parmName) in E:\\src\\BrParms.cs:line 169
at DOffice.BrMan.populateAllFromTextFile(String workDirectory) in E:\\src\\BrMan.cs:line 3218
at DOffice.BrMan.setWorkPath(String pathOfCurrentDoc) in E:\\src\\BrMan.cs:line   1686
at DOffice.Form_Dash.InitWork(Object sender) in E:\\src\\Form_Dash.cs:line 1261

C# : Exception Handling - Locating the error

2 Answers2