what is the correct ways of use try-catch block in C#

Question

i would like to know your opinions of what is the correct way of applying the try-catch block to capture exceptions.

Let say i have 4 levels of hierarchy methods that are calls like this:

method1(){
   method2(){
       method3(){
          method4()
       }
       morecode that depend of what happend in method3
   }
   morecode that depend of what happend in method2
}

So what i do is wrap from inside out the possible methods that are going to present exceptions and as i have code that depends in the different levels of what happen in those methods i propagate the exception using "throw" sentences to avoid that those codes produce a crash.

method1(){
   try
   method2(){
       try
       method3(){
          try
          method4()
          catch
          throw
       }
       catch
       throw
       morecode that depend of what happend in method3
   }
   catch
   return
   morecode that depend of what happend in method2
}

Is this the correct way? or i'm making a terrible use of "throw" sentence?

@Daniel Peñalba: You have that the wrong way around - "throw ex" resets the stack trace. That's bad advice. — Tim Lloyd
– Tim Lloyd, Commented Jan 4, 2011 at 17:25
@Daniel Peñalba: If you recommend it, you don't understand it. There is hardly enough information to assume something or the other. — leppie
– leppie, Commented Jan 4, 2011 at 17:26

Oded · Accepted Answer · 2011-01-04 17:25:36Z

6

If all you are going to do in your catch is re-throw, don't bother with the try at all.

Exceptions will bubble up, so there is no need to catch and re-throw like that - you will still get the correct stack trace.

answered Jan 4, 2011 at 17:25

Oded

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1 Comment

leppie Over a year ago

Good point, many people does this unfortunately (and more than likely incorrectly).

Dekker500 · Accepted Answer · 2011-01-05 11:41:45Z

4

You should catch exceptions at the first level where you want to actually DO something about it.

No need to have multiple try-catch blocks if the end result is the same "generic" action. Just use one catch and handle the errors.

If, however, a catch block changes the result, such that a calling method can react differently, then it should be embedded.

Exception handling is a rather convoluted but important topic...

Suggested title on topic: Robust ASP.Net Exception Handling

edited Jan 5, 2011 at 11:41

answered Jan 4, 2011 at 17:26

Dekker500

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5 Comments

mjsr Over a year ago

that's what happen to me, the catch block are used to return things to normality because in the attempt to run those crashing methods they leave different objects in an incorrect state. Maybe my code is too coupled.

Dekker500 Over a year ago

If, as you say, your exceptions leave code in an incorrect state, then yes, use TRY and FINALLY blocks - de-allocate in the FINALLY block, but allow the exception to bubble up the stack to the point where you really want to handle the exception. Otherwise, you are forever catching-and-throwing exceptions, which can lead to problems down the road. Optionally, use the USING keyword, so if an exception is thrown, it is automatically deallocated (if applicable!)

mjsr Over a year ago

i think i'm getting the idea, i had the incorrect instinct to make the inner pieces of code more robust and capable of handling errors but appears that the correct approach is handle the problems in the more exterior layer possible. I have other related questions. If the inner code is used extensively in other codes, doesn't interest at all?...is manage the exterior layer always the best way?. And one final thing, if the inner code modify objects only known in that context then how can i in the exterior layer reestablish the order?

Dekker500 Over a year ago

As I said, "Exception handling is a rather convoluted topic..." Basically, if the code is re-used but an exception is thrown, clean up the interior code as required, but (after analyzing your own logic) let the layer that must ultimately react to the exception catch it. Try an in-depth book for better understanding of the dynamics (I added a suggested link to my original response, since links in comments don't seem to work)

mjsr Over a year ago

thanks Dekker, i'm going to read that book, and see if i could learn more at respect.

leppie · Accepted Answer · 2011-01-04 17:25:11Z

1

(Personally) I would try workaround every 'exceptional' case, and then only litter the code with try/catch blocks where needed.

answered Jan 4, 2011 at 17:25

leppie

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Comments

Lee Baker · Accepted Answer · 2011-01-04 17:28:11Z

0

The try/catch blocks further down in your call hirachy are only necessary when you have something that needs to be cleaned up in an finally block. If you are just going to throw the exception again you are adding code that is not needed.

You could also use a Using block lower down if the objects implement IDisposable.

answered Jan 4, 2011 at 17:28

Lee Baker

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Comments

petro.sidlovskyy · Accepted Answer · 2011-01-04 17:34:42Z

0

Catch exception only in case you know how to handle it. Other practice is to rethrow new exception by setting original one as inner exception. In some cases it helps to handle exceptions better.

answered Jan 4, 2011 at 17:34

petro.sidlovskyy

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Security Hound · Accepted Answer · 2011-01-04 18:32:46Z

0

You only have to use a single try method, considering if anything fails within the try statement, then the catch statement will happen. You don't want to go throwing exceptions, you want to attempt to handle them, and only throw exceptions when an event happens that you cannot handle.

Design your application in a way so that you can avoid a design like the one you posted.

answered Jan 4, 2011 at 18:32

Security Hound

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1 Comment

mjsr Over a year ago

what you suggest if the inner methods are used intensive in some other place?

tanasi · Accepted Answer · 2011-01-04 19:38:41Z

You can try something like this:

        try
        {
            // Your code
        }
        catch (Exception ex)
        {
            switch (ex.Message)
            {
                case "Some system exception information":                       
                    MessageBox.Show("Your text to replace system exception information",
                     "Warning",
                     MessageBoxButtons.OK, MessageBoxIcon.Warning);  
                    break;      
                default:
                    MessageBox.Show(ex.Message,
                    "Warning",
                    MessageBoxButtons.OK, MessageBoxIcon.Warning);                       
                    break;
             }

         }

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