enum TaskStatus
{
Started,
StillProcessing,
Finished
}
delegate void CallbackDelegate(Task t, TaskStatus status);
class Task
{
public void Start(CallbackDelegate callback)
{
callback(this, TaskStatus.Started);
// calculate PI to 1 billion digits
for (...)
{
callback(this, TaskStatus.StillProcessing);
}
callback(this, TaskStatus.Finished);
}
}
class Program
{
static void Main(string[] args)
{
Task t = new Task();
t.Start(new CallbackDelegate(MyCallbackMethod));
}
static void MyCallbackMethod(Task t, TaskStatus status)
{
Console.WriteLine("The task status is {0}", status);
}
}
private delegate void UpdateHandler(string message);
private UpdateHandler Update;
public void Register(IObserver observer)
{
Update+=observer.Update;
}
public void Unregister(IObserver observer)
{
Update-=observer.Update;
}
public void Notify(string message)
{
Update(message);
}
public Subject()
{
observers = new List<IObserver>();
}
public void Register(IObserver observer)
{
observers.Add(observer);
}
public void Unregister(IObserver observer)
{
observers.Remove(observer);
}
public void Notify(string message)
{
// call update method for every observer
foreach (IObserver observer in observers)
{
observer.Update(message);
}
}
public delegate void UpdateHandler(string message);
private UpdateHandler Update;
public void Register(UpdateHandler observerRoutine)
{
Update+=observerRoutine;
}
public void Unregister(UpdateHandler observerRoutine)
{
Update-=observerRoutine;
}
public void Notify(string message)
{
Update(message);
}
public delegate string TestDelegate();
protected void Page_Load(object sender, EventArgs e)
{
TestDelegate TD1 = new TestDelegate(DiaplayMethodD1);
TestDelegate TD2 = new TestDelegate(DiaplayMethodD2);
TD2 = TD1 + TD2; // Make TD2 as multi-cast delegate
lblDisplay.Text = TD1(); // invoke delegate
lblAnotherDisplay.Text = TD2();
// Note: Using a delegate allows the programmer to encapsulate a reference
// to a method inside a delegate object. Its like the function pointer
// in C or C++.
}
//the Signature has to be same.
public string DiaplayMethodD1()
{
//lblDisplay.Text = "Multi-Cast Delegate on EXECUTION"; // Enable on multi-cast
return "This is returned from the first method of delegate explanation";
}
// The Method can be static also
public static string DiaplayMethodD2()
{
return " Extra words from second method";
}