Best Practice for Exception Handling in a Windows Forms Application?

Question

I\'m currently in the process of writing my first Windows Forms application. I\'ve read a few C# books now so I\'ve got a relatively good understanding of what language feat

Answer 1

All of the advice posted here so far is good and worth heeding.

One thing I'd like to expand on is your question "Do handling exceptions which might be thrown have a performance hit compared with pre-emptively testing things like whether a file on disk exists?"

The naive rule of thumb is "try/catch blocks are expensive." That's not actually true. Trying isn't expensive. It's the catching, where the system has to create an Exception object and load it up with the stack trace, that's expensive. There are many cases in which the exception is, well, exceptional enough that it's perfectly fine to wrap the code in a try/catch block.

For instance, if you're populating a Dictionary, this:

try
{
   dict.Add(key, value);
}
catch(KeyException)
{
}

is often faster than doing this:

if (!dict.ContainsKey(key))
{
   dict.Add(key, value);
}

for every single item you're adding, because the exception only gets thrown when you are adding a duplicate key. (LINQ aggregate queries do this.)

In the example you gave, I'd use try/catch almost without thinking. First, just because the file exists when you check for it doesn't mean that it's going to exist when you open it, so you should really handle the exception anyway.

Second, and I think more importantly, unless your a) your process is opening thousands of files and b) the odds of a file it's trying to open not existing are not trivially low, the performance hit of creating the exception is not something you're ever going to notice. Generally speaking, when your program is trying to open a file, it's only trying to open one file. That's a case where writing safer code is almost certainly going to be better than writing the fastest possible code.