如何在Objective-C中创建策略模式?

[英]How to create a strategy pattern in Objective-C?


I need to develop a strategy pattern where i have a main class with other three classes where i need to refer to the objects of the other three classes using the main class object.To solve this is the strategy pattern will help me? If so please do give me the syntax in Objective-C?

我需要开发一个策略模式,其中我有一个主类和其他三个类,我需要使用主类对象引用其他三个类的对象。要解决这个问题,策略模式会对我有帮助吗?如果是这样,请给我Objective-C中的语法?

2 个解决方案

#1


39  

You'll want to look at Objective-C's protocol mechanism. Here's a simple protocol with a single required method:

您将要了解Objective-C的协议机制。这是一个简单的协议,只需一个方法:

@protocol Strategy <NSObject>

@required
- (void) execute;

@end

Then you declare a class that fulfills that protocol:

然后声明一个满足该协议的类:

@interface ConcreteStrategyA : NSObject <Strategy>
{
    // ivars for A
}
@end

The implementation must provide the -execute method (since it was declared as @required):

实现必须提供-execute方法(因为它被声明为@required):

@implementation ConcreteStrategyA

- (void) execute
{
    NSLog(@"Called ConcreteStrategyA execute method");
}

@end

You can make a similar ConcreteStrategyB class, but I'm not going to show it here.

你可以制作一个类似的ConcreteStrategyB类,但我不会在这里展示它。

Finally, make a context class with a property maintaining the current strategy.

最后,创建一个具有维护当前策略的属性的上下文类。

@interface Context : NSObject
{
    id<Strategy> strategy;
}
@property (assign) id<Strategy> strategy;

- (void) execute;

@end

Here is the implementation. The method that delegates to the strategy's -execute method just happens to be called -execute as well, but it doesn't have to be.

这是实施。委托给策略的-execute方法的方法恰好也被称为-execute,但不一定如此。

@implementation Context

@synthesize strategy;

- (void) execute
{
    [strategy execute];
}

@end

Now I'll make a few instances and put them to use:

现在我将制作一些实例并将它们用于:

ConcreteStrategyA * concreteStrategyA = [[[ConcreteStrategyA alloc] init] autorelease];
ConcreteStrategyB * concreteStrategyB = [[[ConcreteStrategyB alloc] init] autorelease];
Context * context = [[[Context alloc] init] autorelease];

[context setStrategy:concreteStrategyA];
[context execute];
[context setStrategy:concreteStrategyB];
[context execute];    

The console output shows that the strategy was successfully changed:

控制台输出显示策略已成功更改:

2010-02-09 19:32:56.582 Strategy[375:a0f] Called ConcreteStrategyA execute method
2010-02-09 19:32:56.584 Strategy[375:a0f] Called ConcreteStrategyB execute method

Note that if the protocol does not specify @required, the method is optional. In this case, the context needs to check whether the strategy implements the method:

请注意,如果协议未指定@required,则该方法是可选的。在这种情况下,上下文需要检查策略是否实现了该方法:

- (void) execute
{
    if ([strategy respondsToSelector:@selector(execute)])
        [strategy execute];
}

This is a common Cocoa pattern called delegation. For more information on delegation and other design patterns in Cocoa, see this.

这是一种常见的Cocoa模式,称为委托。有关Cocoa中的委派和其他设计模式的更多信息,请参阅此内容。

#2


1  

Here's a bit more of a concrete example. You can put each item in a separate file. I've put it all in one file for ease of understanding.

这里有一个具体的例子。您可以将每个项目放在单独的文件中。为了便于理解,我把它全部放在一个文件中。

//  main.m
//  StrategyWikipediaExample
//
//  Created by steve on 2014-07-08.
//  Copyright (c) 2014 steve. All rights reserved.
//

#import <Foundation/Foundation.h>

/**
 Equivalent to Java Interface
 All concrete Strategies conform to this protocol
 */
@protocol MathOperationsStrategy<NSObject>
- (void)performAlgorithmWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second;
@end

/**
 Concrete Strategies. 
 Java would say they "Extend" the interface.
 */

@interface AddStrategy : NSObject<MathOperationsStrategy>
@end
@implementation AddStrategy
- (void)performAlgorithmWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second
{
    NSInteger result = first + second;
    NSLog(@"Adding firstNumber: %ld with secondNumber: %ld yields : %ld", first, second, result);
}
@end

@interface SubtractStrategy : NSObject<MathOperationsStrategy>
@end
@implementation SubtractStrategy
- (void)performAlgorithmWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second
{
    NSInteger result = first - second;
    NSLog(@"Subtracting firstNumer: %ld with secondNumber: %ld yields: %ld", first, second, result);
}
@end

@interface MultiplyStrategy : NSObject<MathOperationsStrategy>
@end
@implementation MultiplyStrategy
- (void)performAlgorithmWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second
{
    NSInteger result = first * second;
    NSLog(@"Multiplying firstNumber: %ld with secondNumber: %ld yields: %ld", first, second, result);
}
@end

@interface Context : NSObject
@property (weak, nonatomic)id<MathOperationsStrategy>strategy; // reference to concrete strategy via protocol
- (id)initWithMathOperationStrategy:(id<MathOperationsStrategy>)strategy; // setter
- (void)executeWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second;
@end
@implementation Context
- (id)initWithMathOperationStrategy:(id<MathOperationsStrategy>)strategy
{
    if (self = [super init]) {
        _strategy = strategy;
    }
    return self;
}
- (void)executeWithFirstNumber:(NSInteger)first secondNumber:(NSInteger)second
{
    [self.strategy performAlgorithmWithFirstNumber:first secondNumber:second];
}
@end


int main(int argc, const char * argv[])
{

    @autoreleasepool {
        id<MathOperationsStrategy>addStrategy = [AddStrategy new];
        Context *contextWithAdd = [[Context alloc] initWithMathOperationStrategy:addStrategy];
        [contextWithAdd executeWithFirstNumber:10 secondNumber:10];

    }
    return 0;
}
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