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那我们如何才可以引发基类中的事件,给个实例大家一看就明白了。 namespace BaseClassEvents { using System; using System.Collections.Generic; // Special EventArgs class to hold info about Shapes. public class ShapeEventArgs : EventArgs { private double newArea; public ShapeEventArgs(double d) { newArea = d; } public double NewArea { get { return newArea; } } } // Base class event publisher public abstract class Shape { protected double area; public double Area { get { return area; } set { area = value; } } // The event. Note that by using the generic EventHandler<T> event type // we do not need to declare a separate delegate type. public event EventHandler<ShapeEventArgs> ShapeChanged; public abstract void Draw(); //The event-invoking method that derived classes can override. protected virtual void OnShapeChanged(ShapeEventArgs e) { // Make a temporary copy of the event to avoid possibility of // a race condition if the last subscriber unsubscribes // immediately after the null check and before the event is raised. EventHandler<ShapeEventArgs> handler = ShapeChanged; if (handler != null) { handler(this, e); } } } public class Circle : Shape { private double radius; public Circle(double d) { radius = d; area = 3.14 * radius * radius; } public void Update(double d) { radius = d; area = 3.14 * radius * radius; OnShapeChanged(new ShapeEventArgs(area)); } protected override void OnShapeChanged(ShapeEventArgs e) { // Do any circle-specific processing here. // Call the base class event invocation method. base.OnShapeChanged(e); } public override void Draw() { Console.WriteLine("Drawing a circle"); } } public class Rectangle : Shape { private double length; private double width; public Rectangle(double length, double width) { this.length = length; this.width = width; area = length * width; } public void Update(double length, double width) { this.length = length; this.width = width; area = length * width; OnShapeChanged(new ShapeEventArgs(area)); } protected override void OnShapeChanged(ShapeEventArgs e) { // Do any rectangle-specific processing here. // Call the base class event invocation method. base.OnShapeChanged(e); } public override void Draw() { Console.WriteLine("Drawing a rectangle"); } } // Represents the surface on which the shapes are drawn // Subscribes to shape events so that it knows // when to redraw a shape. public class ShapeContainer { List<Shape> _list; public ShapeContainer() { _list = new List<Shape>(); } public void AddShape(Shape s) { _list.Add(s); // Subscribe to the base class event. s.ShapeChanged += HandleShapeChanged; } // ...Other methods to draw, resize, etc. private void HandleShapeChanged(object sender, ShapeEventArgs e) { Shape s = (Shape)sender; // Diagnostic message for demonstration purposes. Console.WriteLine("Received event. Shape area is now {0}", e.NewArea); // Redraw the shape here. s.Draw(); } } class Test { static void Main(string[] args) { //Create the event publishers and subscriber Circle c1 = new Circle(54); Rectangle r1 = new Rectangle(12, 9); ShapeContainer sc = new ShapeContainer(); // Add the shapes to the container. sc.AddShape(c1); sc.AddShape(r1); // Cause some events to be raised. c1.Update(57); r1.Update(7, 7); // Keep the console window open in debug mode. System.Console.WriteLine("Press any key to exit."); System.Console.ReadKey(); } } } /* Output: Received event. Shape area is now 10201.86 Drawing a circle Received event. Shape area is now 49 Drawing a rectangle */
参考How to: Raise Base Class Events in Derived Classes (C# Programming Guide) |
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