Part 18 - Throwing fault exceptions from a WCF service

Suggested Videos
Part 15 - Exception handling in WCF
Part 16 - SOAP faults in WCF
Part 17 - Unhandled exceptions in WCF



This is continuation to Part 17. Please watch Part 17, before proceeding.

In this video we will discuss throwing FaultException from a WCF service. The first question that normally comes to our mind at this point is that, why can't we simply throw .NET exceptions instead of Fault exceptions.



A WCF service should be throwing a FaultException or FaultException<T> instead of Dot Net exceptions. This is because of the following 2 reasons.
1. An unhandled .NET exception will cause the channel between the client and the server to fault. Once the channel is in a faulted state we cannot use the client proxy anymore. We will have to re-create the proxy. We discussed this in Part 17 of the WCF tutorial. On the other hand faultexceptions will not cause the communication channel to fault.

2. As .NET exceptions are platform specific, they can only be understood by a client that is also .NET. If you want the WCF service to be interoperable, then the service should be throwing FaultExceptions.

Please Note: FaultException<T> allows us to create strongly typed SOAP faults. We will discuss this in our next video.

CalculatorService.cs:
using System.ServiceModel;
namespace CalculatorService
{
    public class CalculatorService : ICalculatorService
    {
        public int Divide(int Numerator, int Denominator)
        {
            if (Denominator == 0)
                throw new FaultException("Denomintor cannot be ZERO", new FaultCode("DivideByZeroFault"));

            return Numerator / Denominator;
        }
    }
}

Client application:
using System;
using System.ServiceModel;
using System.Windows.Forms;

namespace WidowsClient
{
    public partial class Form1 : Form
    {
        CalculatorService.CalculatorServiceClient client = null;
        
        public Form1()
        {
            InitializeComponent();
            client = new CalculatorService.CalculatorServiceClient();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                int numerator = Convert.ToInt32(textBox1.Text);
                int denominator = Convert.ToInt32(textBox2.Text);

                label1.Text = client.Divide(numerator, denominator).ToString();
            }
            catch (FaultException faultException)
            {
                label1.Text = faultException.Code.Name + " - " + faultException.Message;
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            client = new CalculatorService.CalculatorServiceClient();
            MessageBox.Show("A new instance of the proxy class is created");
        }
    }
}