C# Nested Try Catch statements or methods?

Question

Simple best practice question.

Should you nest try catch statements or just use methods.

For instance, if you have a method that opens a file does work and closes the file, you would have the open and close outside the try catch, or rather the close in the finally block.

Now if your open method fails, the method would assert right? So should your wrap that in a try catch block or should that be called from another method, which in turn as a try catch block?

Answer 1

In the context of a method that opens a file I would use a using statement vs a try catch. The using statement ensures that Dispose is called if an exception occurs.

using (FileStream fs = new FileStream(file, FileMode.Open))
{
    //do stuff
}

does the same thing as:

FileStream fs;
try
{
     fs = new FileStream(file, FileMode.Open);
     //do Stuff
 }
 finally
 {
        if(fs!=null)
           fs.Dispose();
 }

Answer 2

Now that we have lambdas and type inference and some other stuff, there's an idiom that is common in other languages which now makes a lot of sense in C#. Your example was about opening a file, doing something to it, and then closing it. Well, now, you can make a helper method which opens a file, and also takes care of making sure to close / dispose / clean up, but calls out to a lambda you provide for the "do stuff" portion. This will help you get the complicated try/catch/finally dispose/cleanup stuff right in one place, and then use it over and over.

Here's an example:

public static void ProcessFile(string filePath, Action<File> fileProcessor)
{
  File openFile = null;

  try
  {
    openFile = File.Open(filePath); // I'm making this up ... point is you are acquiring a resource that needs to be cleaned up after.

    fileProcessor(openFile); 
  }
  finally
  {
    openFile.Close(); // Or dispose, or whatever.
  }
}

Now, callers of this method don't have to worry about how to open the file or close / dispose of it. They can do something like this:

Helpers.ProcessFile("C://somefile.txt", f => 
 {
   while(var text = f.ReadLine())
   {
     Console.WriteLine(text);
   }
 });