Chapter 16 Quick Reference

Chapter 16 Quick Reference

To	Do this
Declare a delegate type.	Write the keyword delegate, followed by the return type, followed by the name of the delegate type, followed by any parameter types. For example: delegate void Tick();
Invoke a delegate.	Use the same syntax as a method call. For example: Tick m; ... m();
Create an instance of a delegate.	Use the same syntax you use for a class or struct: write the keyword new, followed by the name of the type (the name of the delegate), followed by the argument between parentheses. The argument must be a method whose signature exactly matches the signature of the delegate. For example: delegate void Tick(); private void Method() { ... }  ...  Tick m = new Tick(this.Method);
Declare an event.	Write the keyword event, followed by the name of the type (the type must be a delegate type), followed by the name of the event. For example: delegate void TickHandler(); class Ticker  {      public event TickHandler Tick;  }
Subscibe to an event.	Create a delegate instance (of the same type as the event), and attach the delegate instance to the event by using the += operator. For example: class Clock  {      ...      public void Start()      {          ticker.Tick += new TickHandler              (this.RefreshTime);      }       private void RefreshTime()      {          ...      }       private Ticker ticker = new Ticker();  } You can also get the compiler to automatically generate the new delegate by just specifying the subscribing method: public void Start()  {      ticker.Tick += this.RefreshTime;  }
Unsubscribe from an event.	Create a delegate instance (of the same type as the event), and detach the delegate instance from the event by using the –= operator. For example: class Clock  {      ...      public void Stop()      {          ticker.Tick - = new TickHandler              (this.RefreshTime);      }       private void RefreshTime()      {          ...      }      private Ticker ticker = new Ticker();  } Or: public void Stop()  {      ticker.Tick -= this.RefreshTime;  }
Raise an event.	Use parentheses exactly as if the event were a method. You must supply arguments to match the type of the event. Don't forget to check whether the event is null. For example: class Ticker  {      public event TickHandler Tick;      ...      private void Notify()      {          if (this.Tick != null)          {              this.Tick();          }      }      ...  }