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CSE459_CSharp_04_Events

CSE459_CSharp_04_Events - Programming in C Events CSE...

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Programming in C# Events Events CSE 494R (proposed course for 459 Programming in C#) Prof. Roger Crawfis
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The event field An event field is just a special delegate instance. Usually exposed as a public field (acts more like a property). Restricts the delegate operations (to the public) to += and -=. Only the class (or its decendents) can fire the event. Only the class (or its descendents) can clear or reset the values (using =).
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Published Properties public class SharedFloat { public delegate void NewValue ( float value); public event NewValue ValueChanging; public event NewValue ValueChanged; private void Dummy( float value) {} public SharedFloat() { // This avoids the check for null. ValueChanging += Dummy; ValueChanged += Dummy; } } private float myFloat; public float Value { get { return myFloat; } set { ValueChanging( value ); myFloat = value ; ValueChanged(myFloat); } }
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Example class Model { public event Notifier notifyViews ; public void Change() { ... notifyViews ("Model"); } } class View { public View(Model m) { m.notifyViews += new Notifier(Update); } void Update(string sender) { Console.WriteLine(sender + " was changed"); } } class Test { static void Main() { Model model = new Model(); new View(model); new View(model); ...
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