Question

I’m currently learning C#, but I am stuck on something and I can’t find a solution for it.
I am trying to create my own Exception class.

The exception is called “InvalidNumberException”, it checks if a number is equal to 5. I know it may seem kinda stupid, but I just need to get the idea about creating Custom Exceptions.

So far I found on MSDN that for creating the Exception I need these four constructors:

public class InvalidNumberException : System.Exception
{
    public InvalidNumbertException() : base() { }
    public InvalidNumberException(string message) : base(message) { }
    public InvalidNumberException(string message, System.Exception inner) : base(message, inner) { }

    // A constructor is needed for serialization when an
    // exception propagates from a remoting server to the client. 
    protected InvalidNumberException(System.Runtime.Serialization.SerializationInfo info,
        System.Runtime.Serialization.StreamingContext context) { }
}

but I don’t know how to implement the method or constructor in this class that a number entered from the console is equal to 5, and if it is not, it throws an exception.

I’ll appreciate if someone helps me with this.

Answer 1

You don’t need all those constructors. Think about the exception you are creating – to ensure an int is != to 5.

So, I would have a single constructor like this:

public InvalidNumberException(int value)
    : base(String.Format("Some custom error message. Value: {0}", value)) { }

And use it like this:

if (number == 5)
    throw new InvalidNumberException(number);

You shouldn’t be wrapping that in a try block. It’s the job of the code that executes the above code block to watch for exceptions, e.g:

try
{
    CallSomeMethodWhichChecksTheNumberAndThrowsIfNecessary();
}
catch (InvalidNumberException inex)
{
    // do something, print to console, log, etc
}

I’m hoping this is just for learning because there is the Int32.Parse and Int32.TryParse methods for this purpose – a custom exception class is not required.