Create a Event

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  1-) Define the EventArgs class that will hold your specific info...

  
  Code Snippet
  class MyStringChangedEventArgs : EventArgs
  {
  private string newValue;

  public MyStringChangedEventArgs(string newValue)

  
  {

  this.newValue = newValue;

  
  }

   

   

  public NewValue

  
  {

  get { return this.newValue; }

  
  }

   

  }

   

  2-) Define the delegate (signature) for the function that will handle such events (I prefer to use the existing EventHandler<T>, being:

  delegate (public delegate void EventHandler<TEventArgs> ( Object sender, TEventArgs e ) where TEventArgs : EventArgs

  3-) Define the event:

  
  Code Snippet
  event EventHandler<MyStringChangedEventArgs> MyStringChanged;

   

  4-) Write code to raise the vent:

  
  Code Snippet
  void OnMyStringChanged(string newValue)
  {
  // you may want to do a bit more research on concurrency issues, since this is not completely safe...
  if (this.MyStringChanged != null)
  {
  this.MyStringChanged(this, new MyStringChangedEventArgs(newValue));
  }
  }

  
  5-) Now we'll implement the setter of the MyString property so that it raises the event:

  
  Code Snippet
  public MyString
  {
  set {
  if (this.myString != value)
  {
  this.myString = value;
  this.OnMyStringChanged(value);
  }
  }

  
  6-) We subscribe to the event that is exposed by your Sample class:

  
  Code Snippet
  Sample sample = new Sample();
  sample.MyStringChanged += HandleMyStringChanged;

  void HandleMyStringChanged(object sender, MyStringChangedEventArgs e)
  {
  MessageBox.Show("MyString has changed to " + e.NewValue);
  }

  
  You may want to look at the INotifyPropertyChanged interface, because this is the one that you would need to implement to make databinding work.. And it's very similar to what you already have:

  
  Code Snippet
  class Sample
  {
   public event PropertyChangedEventHandler PropertyChanged;

   public String MyString
   {
    set
    {
     if (this.myString != value)
     {
      this.myString = value;
      this.OnPropertyChanged("MyString");
     }
    }
   }
   
   public int MyId
   {
    if (this.myId != value)
    {
     this.myId = value;
     this.OnPropertyChanged("MyId");
    }
   }

   private void OnPropertyChanged(string propertyName)
   {
    if (this.PropertyChanged != null)
    {
     this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
   }
  }
  }

  
  And if you databind eg a couple of labels to the Properties you will see that they update as soon as you change their values

  this.label1.DataBindings.Add("Text", mySample, "MyString");
  this.label2.DataBindings.Add("Text", mySample, "MyId");

  mySample.MyString = "something different"; // as soon as you do this, a PropertyChanged event will be raised, and databinding will make sure to update the UI
  

  Sunday, April 29, 2007 3:17 PM