Csharp/CSharp Tutorial/Language Basics/Custom Exception

A custom exception with HelpLink and Source

using System;
public class CustomException : ApplicationException
{
  public CustomException(string Message) : base(Message)
  {
    this.HelpLink = "See the Readme.txt file";
    this.Source = "My Program";
  }
}
class MainClass
{
  public static void Main()
  {
    try
    {
      Console.WriteLine("Throwing a new CustomException object");
      throw new CustomException("My CustomException message");
    }
    catch (CustomException e)
    {
      Console.WriteLine("HelpLink = " + e.HelpLink);
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("Source = " + e.Source);
      Console.WriteLine("StackTrace = " + e.StackTrace);
      Console.WriteLine("TargetSite = " + e.TargetSite);
    }
  }
}

Throwing a new CustomException object
HelpLink = See the Readme.txt file
Message = My CustomException message
Source = My Program
StackTrace =    at MainClass.Main()
TargetSite = Void Main()

Create your own exception class based on Exception

using System;
using System.Collections;
public class MyException : Exception
{
    public MyException( String reason, Exception inner ) :base( reason, inner ) {
    }
}
public class MainClass
{
    static void Main() {
        try {
            try {
                ArrayList list = new ArrayList();
                list.Add( 1 );
                Console.WriteLine( "Item 10 = {0}", list[10] );
            }
            catch( ArgumentOutOfRangeException x ) {
                throw new MyException( "I"d rather throw this",x ) ;
            }
            finally {
                Console.WriteLine( "Cleaning up..." );
            }
        }
        catch( Exception x ) {
            Console.WriteLine( x );
            Console.WriteLine( "Done" );
        }
    }
}

Cleaning up...
MyException: I"d rather throw this ---> System.ArgumentOutOfRangeException: Index was out of range.
Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.Collections.ArrayList.get_Item(Int32 index)
   at MainClass.Main()
   --- End of inner exception stack trace ---
   at MainClass.Main()
Done

CustomException is an application exception that supports remoting.

using System;
using System.Reflection;
using System.Runtime.Serialization;
[assembly: AssemblyVersion("1.1.0.0")]
[assembly: AssemblyCultureAttribute("")]

[Serializable]
public class CustomException : Exception {
    public CustomException(): base("custom exception", null) {
        prop_Time = DateTime.Now.ToLongDateString() + " " + DateTime.Now.ToShortTimeString();
    }
    protected CustomException(SerializationInfo info,StreamingContext context)
        : base(info, context) {
        prop_Time = info.GetString("Time");
    }
    public override void GetObjectData(SerializationInfo info, StreamingContext context) {
        info.AddValue("Time", prop_Time, typeof(string));
        base.GetObjectData(info, context);
    }
    protected string prop_Time = null;
    public string Time {
        get {
            return prop_Time;
        }
    }
}

Derived exceptions must appear before base class exceptions.

using System; 
 
class MyException : ApplicationException { 
  public MyException() : base() { } 
  public MyException(string str) : base(str) { } 
 
  public override string ToString() { 
    return Message; 
  } 
} 
 
class MyDerivedException : MyException { 
  public MyDerivedException() : base() { } 
  public MyDerivedException(string str) : base(str) { } 
 
  public override string ToString() { 
    return Message;  
  } 
} 
 
class MainClass { 
  public static void Main() { 
    for(int x = 0; x < 3; x++) { 
      try { 
        if(x==0) 
           throw new MyException("Caught an MyException exception"); 
        else if(x==1) 
           throw new MyDerivedException("Caught an MyDerivedException exception"); 
        else 
           throw new Exception(); 
      } 
      catch (MyDerivedException exc) { 
        // catch the exception 
        Console.WriteLine(exc); 
      } 
      catch (MyException exc) { 
        // catch the exception 
        Console.WriteLine(exc); 
      } 
      catch (Exception exc) { 
        Console.WriteLine(exc); 
      } 
    } 
  } 
}

Caught an MyException exception
Caught an MyDerivedException exception
System.Exception: Exception of type "System.Exception" was thrown.
   at MainClass.Main()

Extends Exception

using System;
using System.Runtime.Serialization;
[Serializable]
public sealed class MyException : Exception
{
    private string stringInfo;
    private bool booleanInfo;
    public MyException() : base() { }
    public MyException(string message) : base(message) { }
    public MyException(string message, Exception inner): base(message, inner) { }
    private MyException(SerializationInfo info, StreamingContext context) : base(info, context)
    {
        stringInfo = info.GetString("StringInfo");
        booleanInfo = info.GetBoolean("BooleanInfo");
    }
    public MyException(string message, string stringInfo, bool booleanInfo) : this(message)
    {
        this.stringInfo = stringInfo;
        this.booleanInfo = booleanInfo;
    }
    public MyException(string message, Exception inner, string stringInfo, bool booleanInfo): this(message, inner)
    {
        this.stringInfo = stringInfo;
        this.booleanInfo = booleanInfo;
    }
    public string StringInfo
    {
        get { return stringInfo; }
    }
    public bool BooleanInfo
    {
        get { return booleanInfo; }
    }
    public override void GetObjectData(SerializationInfo info, StreamingContext context)
    {
        info.AddValue("StringInfo", stringInfo);
        info.AddValue("BooleanInfo", booleanInfo);
        base.GetObjectData(info, context);
    }
    public override string Message
    {
        get
        {
            string message = base.Message;
            if (stringInfo != null)
            {
                message += Environment.NewLine + stringInfo + " = " + booleanInfo;
            }
            return message;
        }
    }
}
public class MainClass
{
    public static void Main()
    {
        try
        {
            throw new MyException("Some error", "SomeCustomMessage", true);
        } 
        catch (MyException ex)
        {
            Console.WriteLine(ex.Message);
            Console.WriteLine(ex.BooleanInfo);
            Console.WriteLine(ex.StringInfo);
        }
    }
}

Some error
SomeCustomMessage = True
True
SomeCustomMessage

Use a custom Exception

using System;  
  
class RangeArrayException : ApplicationException { 
  public RangeArrayException() : base() { } 
  public RangeArrayException(string str) : base(str) { }  
 
  public override string ToString() { 
    return Message; 
  } 
} 
 
      
class MainClass {   
  public static void Main() {   
    try { 
         throw new RangeArrayException("Low index not less than high.");  
    } catch (RangeArrayException exc) { 
       Console.WriteLine(exc); 
    } 
  }  
}

Low index not less than high.

User-Defined Exception Classes

using System;
public class CountIsZeroException: ApplicationException{
    public CountIsZeroException(){
    }
    public CountIsZeroException(string message) : base(message)
    {
    }
    public CountIsZeroException(string message, Exception inner) : base(message, inner)
    {
    }
}
class MainClass{
    public static void Main() {
        try {
            DoAverage();
        }
        catch (CountIsZeroException e)
        {
            Console.WriteLine("CountIsZeroException: {0}", e);
        }
    }
    public static void DoAverage() {
        throw(new CountIsZeroException("Zero count in DoAverage"));
    }
}

CountIsZeroException: CountIsZeroException: Zero count in DoAverage
   at MainClass.DoAverage()
   at MainClass.Main()