WinForms / WPF中的异常处理

Question

What is the best practice for exception handling in WinForms or WPF. I haven't found a satisfying solution so far. Some people suggest to catch the unhandled exception event. But I don't think that this is a good solution.

The problem

I have a 3 layer application. The persistence layer, the business layer and the ui layer. Instead of catching exceptions in all three layers I think the correct place to catch the exceptions are in the ui layer. So the user will get an error message and maybe there is also a way the user can 'solve' the issue (wrong data input, etc).

So the question is, is the best/correct way to surround EVERY ui-eventhandler (click event, selection changed event, etc) with a try catch block? Like this:

private void button_MouseUp(object sender, MouseButtonEventArgs e)
{
   try
   {
      /// ...
   }
   catch (Exception ex)
   {
      // log exception
      // show error to user if necessary
   }
}

I know that catching all exceptions is bad. And of course you need to prevent exceptions by validating the user input data. But sometimes there will be bugs ;).

Imagine the following situation: The user makes some changes which aren't saved yet. Then he clicks a button and in the button handler is a bug. So wouldn't it be better to show a error message and let the user decide when he wants to quit the application, so that the user won't lose the unsaved data?

Answer 1

So the question is, is the best/correct way to surround EVERY ui-eventhandler (click event, selection changed event, etc) with a try catch block?

No. The only thing you do is to repeat yourself (violation of DRY). If you in the future want to change how exceptions are logged you have to go through every method that has a try/catch block.

You can use the Application.ThreadException event to catch all unhandled exceptions (in the UI thread) to display an error dialog to the user and log the exception.

The best way is of course to make sure that the user have supplied correct information by validating it. By doing so all exceptions that occurs are truly exceptions and not something that you could have prevented.

Here are my golden rules:

1. Always try to prevent exceptions by making sure that the supplied data is correct.
2. Only catch exceptions that you can use to resolve the situation without user involvement.
3. Use Application.ThreadException event for all other errors (and log them).

You can read my exceptions series if you want to: http://blog.gauffin.org/2013/04/what-is-exceptions/