Design Pattern: Abstract Factory 模式

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假设您要制作一个对话方块（Dialog）元件，您希望的是这个对话方块可以有不同的视感（Look-and- feel），最基本的想法是，藉由Setter将不同视感的元件设定给这个对话方块，例如：

• CustomDialog.java

   1: public class CustomDialog {

   2:     private IButton button;

   3:     private ITextField textField;

   4:     

   5:     public void setButton(IButton button) {

   6:         this.button = button;    

   7:     }

   8:     

   9:     public void setTextField(ITextField textField) {

  10:         this.textField = textField;

  11:     }

  12:  

  13:     public void layoutAllComponents() {

  14:         // ....

  15:     }

  16:     

  17:     public void showDialog() {

  18:         this.paintDialog();

  19:         button.paintButton();

  20:         textField.paintTextField();

  21:     }

  22:   

  23:     public void paintDialog() {

  24:         System.out.println("custom dialog paints....");

  25:     }

  26: }

很简单，这是最基本的介面依赖，Setter依赖于IButton与ITextField两个介面，而不是其实作类别，不过这边还有个进一步的要求，使用 上面的方式还必须亲自呼叫Setter、layout等方法，您希望视感的更换可以更简单些，例如只要透一个元件的替换就可以完成对话方块上所有元件的视 感更换。
您可以使用Abstract Factory模式，将所有对话方块所需要的产生的元件加以封装，对话方块依赖于Abstract Factory，实际上具体的Factory实现则分别产生对话方块所需要的视感元件，下面的 UML 类别图展现这种概念。

现在如果要更换所有的视感元件，就只要抽象掉具体的Factory就可以了，例如：

   1: CustomDialog windowsDialog =

   2:  new CustomDialog(new WindowsWidgetFactory());

   3: windowsDialog.showDialog();

   4: CustomDialog macDialog =

   5:  new CustomDialog(new MacWidgetFactory());

   6: macDialog.showDialog();

来将上面的UML图具体实现出来。

• CustomDialog.java

   1: public class CustomDialog {

   2:     private IButton button;

   3:     private ITextField textField;

   4:     

   5:     public CustomDialog(IWidgetFactory widgetFactory) {

   6:         setWidgetFactory(widgetFactory);

   7:     }

   8:     

   9:     // 由于客户端只依赖于抽象的工厂，工厂如何实作并无关客户端的事

  10:     // 要抽换工厂并不需要改动客户端的程式

  11:     public void setWidgetFactory(IWidgetFactory widgetFactory) {

  12:         setButton(widgetFactory.getButton());

  13:         setTextField(widgetFactory.getTextField());

  14:      

  15:     }

  16:  

  17:     public void layoutAllComponents() {

  18:         // layout all components

  19:     }

  20:     

  21:     // 这边也是依赖抽象，实际改变了元件实例

  22:     // 客户端代码也不用更改

  23:     public void setButton(IButton button) {

  24:         this.button = button;    

  25:     }

  26:     

  27:     public void setTextField(ITextField textField) {

  28:         this.textField = textField;

  29:     }

  30:     

  31:     public void showDialog() {

  32:         this.paintDialog();

  33:         button.paintButton();

  34:         textField.paintTextField();

  35:     }

  36:   

  37:     public void paintDialog() {

  38:         System.out.println("custom dialog paints....");

  39:     }

  40: } 

• IButton.java

   1: public interface IButton {

   2:     public void paintButton();

   3: } 

• ITextField.java

   1: public interface ITextField {

   2:     public void paintTextField();

   3: } 

• IWidgetFactory.java

   1: public interface IWidgetFactory {

   2:     public IButton getButton();

   3:     public ITextField getTextField();

   4: } 

• MacButton.java

   1: public class MacButton implements IButton {

   2:     public void paintButton() {

   3:         System.out.println("Mac button paints....");

   4:     }

   5: } 

• WindowsButton.java

   1: public class WindowsButton implements IButton {

   2:     public void paintButton() {

   3:         System.out.println("Windows button paints....");

   4:     }

   5: } 

• MacTextField.java

   1: public class MacTextField implements ITextField {

   2:     public void paintTextField() {

   3:         System.out.println("Mac textField paints....");

   4:     }

   5: } 

• WindowsTextField.java

   1: public class WindowsTextField implements ITextField {

   2:     public void paintTextField() {

   3:         System.out.println("Windows textField paints....");

   4:     }

   5: } 

• MacWidgetFactory.java

   1: public class MacWidgetFactory implements IWidgetFactory {

   2:     public IButton getButton() {

   3:         return new MacButton();

   4:     }

   5:     

   6:     public ITextField getTextField() {

   7:         return new MacTextField();

   8:     }

   9: } 

• WindowsWidgetFactory.java

   1: public class WindowsWidgetFactory 

   2:                           implements IWidgetFactory {

   3:     public IButton getButton() {

   4:         return new WindowsButton();

   5:     }

   6:     

   7:     public ITextField getTextField() {

   8:         return new WindowsTextField();

   9:     }

  10: }

下图是Abstract Factory模式的UML结构图：

简单的说，在Abstract Factory模式中将具体的Product封装在具体Factory实现中，而客户仍只要面对Factory与Product的抽象介面，避免依赖于具 体的Factory与Product，由于Factory封装了所必须的Product，所以要更换掉所有的元件，只要简单的抽换掉Factory就可以 了，不用修改客户端的程式。

Edit bt Atlas

Time 2013/7/1 09:49