设计模式[4] Bridge Pattern 桥接模式

decouple an abstraction from its implementation so that the two can vary independently" (Gamma et al.)
接口和实现分离，接口和实现的修改可以互不干扰。

参与者：

• Abstraction   (IShape) 
  • defines the abstraction's interface.
  • maintains a reference to an object of type Implementor. 主要就是这个reference。
• RefinedAbstraction   (CircleShape)
  • extends the interface defined by Abstraction.
• Implementor   (IDrawingAPI)
  • defines the interface for implementation classes. This interface doesn't have to correspond exactly to Abstraction's interface; in fact the two interfaces can be quite different. Typically the Implementation interface provides only primitive operations, and Abstraction defines higher-level operations based on these primitives. 和Abstraction的接口没啥关系。
    
• ConcreteImplementor   (DrawingAPI1, DrawingAPI2)
  • implements the Implementor interface and defines its concrete implementation.

using System;
 
 /**//** "Implementor" */
 interface IDrawingAPI ...{
    void DrawCircle(double x, double y, double radius);
 }
 
 /**//** "ConcreteImplementor" 1/2 */
 class DrawingAPI1 : IDrawingAPI ...{
    public void DrawCircle(double x, double y, double radius) 
    ...{
        System.Console.WriteLine("API1.circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /**//** "ConcreteImplementor" 2/2 */
 class DrawingAPI2 : IDrawingAPI 
 ...{
    public void DrawCircle(double x, double y, double radius) 
    ...{ 
        System.Console.WriteLine("API2.circle at {0}:{1} radius {2}", x, y, radius); 
    }
 }
 
 /**//** "Abstraction" */
 interface IShape ...{
    void Draw();                             // low-level (i.e. Implementation-specific)
    void ResizeByPercentage(double pct);     // high-level (i.e. Abstraction-specific)
 }
 
 /**//** "Refined Abstraction" */
 class CircleShape : IShape ...{
    private double x, y, radius;
    private IDrawingAPI drawingAPI;
    public CircleShape(double x, double y, double radius, IDrawingAPI drawingAPI) 
    ...{
        this.x = x;  this.y = y;  this.radius = radius; 
        this.drawingAPI = drawingAPI;
    }
    // low-level (i.e. Implementation-specific)
    public void Draw() ...{ drawingAPI.DrawCircle(x, y, radius); }
    // high-level (i.e. Abstraction-specific)
    public void ResizeByPercentage(double pct) ...{ radius *= pct; }
 }
 
 /**//** "Client" */
 class BridgePattern ...{
    public static void Main(string[] args) ...{
        IShape[] shapes = new IShape[2];
        shapes[0] = new CircleShape(1, 2, 3, new DrawingAPI1());
        shapes[1] = new CircleShape(5, 7, 11, new DrawingAPI2());
 
        foreach (IShape shape in shapes) ...{
            shape.ResizeByPercentage(2.5);
            shape.Draw();
        }
    }
 }