Objective C--工厂方法模式

  今天和大家分享的设计模式是工厂方法模式。

  首先给出工厂方法模式的一个简单的定义:

工厂方法模式(Factory Method)，定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法使一个类的实例化延迟到其子类。

  早在第一次和大家分享的关于简单工厂模式中就有提到过一次关于“工厂类”模式。为了帮助大家能够回忆一下简单工厂模式，在这里提一下简单工厂模式的优点，简单工厂模式的最大优点在于工厂类中包含了必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对于客户端来说，去除了与具体产品的依赖。其实，工厂方法模式是简单工厂模式的进一步抽象和推广。由于使用了多态性，工厂方法模式保持了简单工厂模式的优点，而且克服了它的缺点。但缺点是，由于每加一个产品，就需要加一个产品工厂的类，增加了额外的开发量。

  下面还是以计算器为例子，详细介绍工厂方法模式，还是老样子，先向大家展示一下类结构图。

  上面这张图向大家展示了各个类之间的关系。其实和简单工厂模式不同的是，类图的右边抽象工厂接口是相比简单工厂模式多出来的抽象接口。

  下面直接上代码吧，别的不多说了。

• Operation类接口

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#import <Foundation/Foundation.h> @interface Operation: NSObject { double numberA; double numberB; } @property double numberA; @property double numberB; -( double ) GetResult; @end

• Operation类实现

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#import "Operation.h" @implementation Operation @synthesize numberA, numberB; -( double ) GetResult{ return -1.0; } @end

• OperationAdd类接口

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#import "Operation.h" @interface OperationAdd :Operation @end

• OperationAdd类实现

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#import "OperationAdd.h" @implementation OperationAdd -( double ) GetResult{ double result =0; result = numberA+numberB; return result; } @end

• OperationDiv类接口

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#import "Operation.h" @interface OperationDiv:Operation @end

• OperationDiv类实现

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#import "OperationDiv.h" @implementation OperationDiv -( double )GetResult{ double result =0; @try { result = numberA/numberB; } @catch ( NSException *exception) { NSLog (@ "除数不能为0" ); } return result; } @end

• OperationMul类接口

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#import "Operation.h" @interface OperationMul:Operation @end

• OperationMul类实现

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#import "OperationMul.h" @implementation OperationMul -( double )GetResult{ double result =0; result = numberA*numberB; return result; } @end

• OperationSub类接口

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#import "Operation.h" @interface OperationSub :Operation @end

• OperationSub类接口

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#import "OperationSub.h" @implementation OperationSub -( double )GetResult{ double result =0; result = numberA-numberB; return result; } @end

• IFactory类接口

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#import <Foundation/Foundation.h> #import "Operation.h" @interface IFactory : NSObject -(Operation*)CreateOperation; @end

• IFactory类实现

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#import "IFactory.h" @implementation IFactory -(Operation*)CreateOperation{ return [[Operation alloc]init]; } @end

• AddFactory类接口

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#import "IFactory.h" @interface AddFactory:IFactory @end

• AddFactory类实现

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#import "AddFactory.h" #import "OperationAdd.h" @implementation AddFactory -(Operation*)CreateOperation{ return [[OperationAdd alloc]init]; } @end

• SubFactory类接口

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#import "IFactory.h" @interface SubFactory:IFactory @end

• SubFactory类实现

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#import "SubFactory.h" #import "OperationSub.h" @implementation SubFactory -(Operation*)CreateOperation{ return [[OperationSub alloc]init]; } @end

• MulFactory类接口

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#import "IFactory.h" @interface MulFactory:IFactory @end

• MulFactory类实现

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#import "MulFactory.h" #import "OperationMul.h" @implementation MulFactory -(Operation*)CreateOperation{ return [[OperationMul alloc]init]; } @end

• DivFactory类接口

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#import "IFactory.h" @interfaceDiv Factory:IFactory @end

• DivFactory类实现

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#import "DivFactory.h" #import "OperationDiv.h" @implementation DivFactory -(Operation*)CreateOperation{ return [[OperationDiv alloc]init]; } @end

• Main方法调用

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#import <Foundation/Foundation.h> #import "OperationAdd.h" #import "AddFactory.h" //加法工厂,你可以根据需要添加其他运算工厂 int main ( int argc, const char * argv[]) { @autoreleasepool { IFactory *operFactory = [[AddFactory alloc]init]; Operation *oper = [operFactory CreateOperation]; [oper setNumberA:1]; [oper setNumberB:2]; double result = [oper GetResult]; NSLog (@ "The result is %f" , result); } return 0; }

  好啦，上面就是工厂方法模式的Objective C的类代码。