Event Handling C# 2.0

[email protected] · January 25th, 2008, 03:19 AM

Hi All,

I am working on a project that requires handling of custom events. Some class will raise the DataEvent of RaiseEventClass. I have to implement event handler for the DataEvent in the RaiseEventClass. Please help me how to implement event handler. Please show some codes if possible.
Below is the skeleton of the class.
Thanks in advance!

public class RaiseEventClass
{
    public delegate void RaiseEventDelegate(ArrayList files);
    public event RaiseEventDelegate DataEvent;

    public void SearchFiles(ArrayList list)
    {
       DataEvent(list); //raising event for testing
    }

}

A.Asif

samjudson · January 25th, 2008, 04:39 AM

You should check for null when raising events in C#

if( DataEvent != null ) DataEvent(list);

Also, usually event delegates follow the format of:

void EventName(object sender, EventArgs e)

where e is either the EventArgs class or some class that derives from it. In this case something like the following is best:

Code:

  public class DataEventArgs : EventArgs
  {
     private ArrayList _list;
     public ArrayList FileList { get { return _list; } set { _list = value; } }
  }
  public void DataEventEventHandler(object sender, DataEventArgs e)
  public event DataEventEventHandler DataEvent;

  public void SearchFiles(ArrayList list)
  {
    DataEventArgs e = new DataEventArgs();
    e.FileList = list;

    if( DataEvent != null ) DataEvent(this, e); //raising event for testing
  }

To consume the event you then do the usual:

[code]
RaiseEventClass c = new RaiseEventClass();
c.DataEvent += new DataEventEventHandler(My_DataEvent);

//elsewhere define the method
public void My_DataEvent(object sender, DataEventArgs e)
{
// Do something with the list...
// e.FileList
}

/- Sam Judson : Wrox Technical Editor -/

Bob Bedell · January 25th, 2008, 11:37 AM

Don't forget the delegate...:)

Code:

public void DataEventEventHandler(object sender, DataEventArgs e)

should be:

Code:

public delegate void DataEventEventHandler(object sender, DataEventArgs e);

Also just wanted to add using the DataEventArgs constructor and the OnEventName convention in the event publisher class:

Code:

public class DataEventArgs : EventArgs {

        private ArrayList _list;

        public ArrayList FileList 
        { 
            get { return _list; } 
            set { _list = value; }
        }

        public DataEventArgs(ArrayList list)
        {
            this._list = list;
        }
    }

class EventPublisher {

        public event DataEventEventHandler DataEvent;

        public void CreateList() 
        {
            ArrayList list = new ArrayList();
            list.Add("Test");
            SearchFiles(list);
        }

        private void SearchFiles(ArrayList list) {

            DataEventArgs e = new DataEventArgs(list);
            this.OnDataEvent(e);
        }

        protected virtual void OnDataEvent(DataEventArgs e)
        {
            if (DataEvent != null)
                DataEvent(this, e);
        }
    }

class EventSubscriber {

        static void Main() 
        {
            EventPublisher eventPublisher = new EventPublisher();
            eventPublisher.DataEvent += new DataEventEventHandler(eventPublisher_DataEvent);

            eventPublisher.CreateList();
        }

        static void eventPublisher_DataEvent(object sender, DataEventArgs e) {
            Console.WriteLine(e.FileList[0]);
            Console.Read();
        }
    }

Best,

Bob