随笔- 281 文章- 130 评论- 674 阅读- 321万

设计模式(6)-装饰器（认识程序中的装饰器）

之前已经看过装饰器模式，但是感觉不是很清晰，但是有一种情况下出的代码，一定是装饰器。

Widget* aWidget = new BorderDecorator(
        new BorderDecorator(
        new ScrollDecorator(
        new TextField( 80, 24 ))));

可以看到，层层嵌套，每个类都可以按照一定的顺序嵌套多次。

比如将顺序改为如下：

Widget* bWidget = new ScrollDecorator(
        new BorderDecorator(
        new ScrollDecorator(
        new TextField( 80, 24 ))));

出现的结果就会不一样，看一下完整的代码。

#include <iostream>
 
using namespace std;
 
/* Component (interface) */
class Widget {
     
public: 
    virtual void draw() = 0; 
    virtual ~Widget() {}
}; 
 
/* ConcreteComponent */
class TextField : public Widget {
     
private:                  
    int width, height;
     
public:
    TextField( int w, int h ){ 
        width  = w;
        height = h; 
    }
     
    void draw() { 
        cout << "文本框: " << width << ", " << height << '\n'; 
    }
};
 
/* Decorator (interface) */                                          
class Decorator : public Widget {
     
private:
    Widget* wid;       // reference to Widget
     
public:
    Decorator( Widget* w )  { 
        wid = w; 
    }
     
    void draw() { 
        wid->draw(); 
    }
     
    ~Decorator() {
        delete wid;
    }
};
 
/* ConcreteDecoratorA */
class BorderDecorator : public Decorator { 
     
public:
    BorderDecorator( Widget* w ) : Decorator( w ) { }
    void draw() {
        Decorator::draw();    
        cout << "   添加边框" << '\n'; 
    }  
};
 
/* ConcreteDecoratorB */
class ScrollDecorator : public Decorator { 
public:
    ScrollDecorator( Widget* w ) : Decorator( w ) { }
    void draw() {
        Decorator::draw(); 
        cout << "   添加滚动" << '\n';
    }  
};
 
int main( void ) {
     
    Widget* aWidget = new BorderDecorator(
        new BorderDecorator(
        new ScrollDecorator(
        new TextField( 80, 24 ))));
    aWidget->draw();
    delete aWidget;
     
    Widget* bWidget = new ScrollDecorator(
        new BorderDecorator(
        new ScrollDecorator(
        new TextField( 80, 24 ))));
    bWidget->draw();
    delete bWidget;
    return 0;
}