How do I pass objects in EventArgs

Question

I have a usercontrol that raises an event after communicating with a web service. The parent handles this event when raised. What I thought would be the proper approach would be to pass the object returned from the webservice to the parent as eventargs???

If this is the proper way I can't seem to find the instructions on how to do so.

UserControl

public event EventHandler LoginCompleted; 

then later after the service returns biz object:

if (this.LoginCompleted != null)         {             this.LoginCompleted(this, new EventArgs() //this is where I would attach / pass my biz object no?);           } 

Parent

ctrl_Login.LoginCompleted += ctrl_Login_LoginCompleted; ....snip.... void ctrl_Login_LoginCompleted(object sender, EventArgs e)     {         //get my object returned by login     } 

So my question is what would be the "approved" method for getting the user object back to the parent? Create a property class that everything can access and put it there?

Answer 1

You would have to declare your event using EventHandler<T> where T is your class that derives from EventArgs:

public event EventHandler<LoginCompletedEventArgs> LoginCompleted; 

LoginCompletedEventArgs could look like this:

public class LoginCompletedEventArgs : EventArgs {     private readonly YourBusinessObject _businessObject;      public LoginCompletedEventArgs(YourBusinessObject businessObject)     {         _businessObject = businessObject;     }      public YourBusinessObject BusinessObject     {         get { return _businessObject; }     } } 

Usage would be like this:

private void RaiseLoginCompleted(YourBusinessObject  businessObject) {     var handler = LoginCompleted;     if(handler == null)         return;      handler(this, new LoginCompletedEventArgs(businessObject)); } 

Please notice how I implemented RaiseLoginCompleted. This is a thread-safe version of raising the event. I eliminates a possible NullReferenceException that can occur in a race condition scenario where one thread wants to raise the event and another thread un-subscribes the last handler after the if check but before actually invoking the handler.

Answer 2

Well, you could do all that or you could define a delegate as your EventHandler and define your properties in its signature.

Such as:

public delegate void MyEventEventHandler(int prop1, string prop2, object prop3...);  public event MyEventEventHandler MyEvent;