#856 – Choosing an Exception Type to Throw

When you throw an exception, you create and populate an instance of the System.Exception class, or one of its derived classes.

While it’s possible to throw an exception of type System.Exception, it’s not normally recommended.  You typically want to throw as specific an exception as possible, for two reasons:

• To provide some specific details about what went wrong (e.g. filename that could not be found, rather than just a general message).
• To allow an exception handler to catch specific types of exceptions

Typically, when throwing an exception, you do one of the following:

• Throw an exception whose type matches one of the predefined exception types in the .NET Framework.  (E.g. System.ArgumentException)
• Throw an instance of System.ApplicationException and provide a relevant message
• Define your own custom exception type, which inherits from System.Exception, and throw an instance of that type.

#855 – Throwing an Exception

Your code can throw an exception to indicate that some sort of error occurred.  You’ll typically do this to indicate that something has gone wrong and the execution of the method cannot continue.

To throw an exception, you create an instance of the System.Exception class, or one of its derived classes, to contain information about what went wrong.  You use the throw statement to throw the exception.  Control returns immediately to the calling function and the exception “bubbles up” the call stack, looking for a calling method that can handle the exception.

Below, an exception is thrown if numTimesToBark is too large.

        public void Bark(int numTimesToBark)
        {
            if (numTimesToBark > 10)
            {
                string message =
                    string.Format("Dogs can bark at most 10 times.  {0} is too much barking",
                                  numTimesToBark);
                Exception exc = new Exception(message);
                throw exc;
            }

            for (int i = 0; i < numTimesToBark; i++)
                Console.WriteLine("Woof");
        }