iOS App开发如何应用设计模式中的命令模式

来自:互联网
时间:2023-04-15
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命令模式封装一个请求或行为作为一个对象。封装的请求比原的更加灵活,可以在对象之间传递,储存,动态修改,或放入一个队列。

那么让我们简要的说一下命令模式的特点。

  • 它能比较容易地设计一个命令队列;
  • 在需要的情况下,可以较容易地将命令记入日志;
  • 允许接收请求地一方决定是否要否决请求;
  • 可以容易地实现对请求地撤销和重做;
  • 由于加进新地具体命令类不影响其他的类,因此增加新的具体命令类很容易;
  • 把请求一个操作的对象与知道怎么执行一个操作的对象分隔开。

下面给出基本的类结构图:

iOS App开发如何应用设计模式中的命令模式

上面这张图是命令模式的类结构的基本图。其实从这张图中还可以扩展出很多,细节就不说了,给大家留一些想象的空间,呵呵!

还是老规矩,下面给出实例:

Objective-C 示例:

Command:


//
//  NimoCommand.h
//  CommandDemo
//
 
#import
 
@protocol NimoCommand
 
- (void)execute;
 
@end


ConcreteCommand:


//
//  NimoConcreteCommand.h
//  CommandDemo
//
#import
#import "NimoCommand.h"
@class NimoReceiver;
 
@interface NimoConcreteCommand : NSObject
 
@property (nonatomic) NimoReceiver *receiver;
 
- (id)initWithReceiver:(NimoReceiver *)receiver;
 
@end
//
//  NimoConcreteCommand.m
//  CommandDemo
//
 
#import "NimoConcreteCommand.h"
#import "NimoReceiver.h"
 
 
@implementation NimoConcreteCommand
 
- (void)execute
{
    [_receiver action];
}
 
- (id)initWithReceiver:(NimoReceiver *)receiver
{
    if (self = [super init]) {
        _receiver = receiver;
    }
    
    return self;
}
 
@end


Receiver:


//
//  NimoReceiver.h
//  CommandDemo
//

 

#import
 
@interface NimoReceiver : NSObject
 
- (void)action;
 
@end


//
//  NimoReceiver.m
//  CommandDemo
//

 

#import "NimoReceiver.h"
 
@implementation NimoReceiver
 
- (void)action
{
    NSLog(@"实际执行");
}
 
@end


Invoker:


//
//  NimoInvoker.h
//  CommandDemo
//
 
#import
#import "NimoCommand.h"
 
@interface NimoInvoker : NSObject
 
@property (nonatomic, weak) id command;
 
- (void)executeCommand;
 
@end
//
//  NimoInvoker.m
//  CommandDemo
//
 
#import "NimoInvoker.h"
 
 
@implementation NimoInvoker
 
- (void)executeCommand
{
    [_command execute];
}
 
@end


Client:


//
//  main.m
//  CommandDemo
//

 

#import
#import "NimoReceiver.h"
#import "NimoInvoker.h"
#import "NimoConcreteCommand.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
       
        NimoReceiver *receiver = [[NimoReceiver alloc] init];
        NimoConcreteCommand *command = [[NimoConcreteCommand alloc] initWithReceiver:receiver];
        
        NimoInvoker *invoker = [[NimoInvoker alloc] init];
        invoker.command = command;
        [invoker executeCommand];
        
    }
    return 0;
}


Running:

2015-08-13 22:49:56.412 CommandDemo[1385:43303] 实际执行

Cocoa Touch框架中的命令模式:

NSInvocation对象

如下示例,Client没有直接调用Receiver的方法,而是用NSInvocation对象封装了运行时库向Receiver发送执行消息所需的所有必要信息,这里的NSInvocation对象类似于上文中的ConcreteCommand对象。

Receiver:


//
//  NimoReceiver.h
//  InvocationDemo
//

 

#import
 
@interface NimoReceiver : NSObject
 
- (int)printWithName:(NSString *)name gender:(NSString *)gender age:(int)age;
 
@end


//
//  NimoReceiver.m
//  InvocationDemo
//

 

#import "NimoReceiver.h"
 
@implementation NimoReceiver
 
- (int)printWithName:(NSString *)name gender:(NSString *)gender age:(int)age
{
    NSLog(@"My name is %@, %@, %d years old.", name, gender, age);
    return 119;
}
 
@end


Client:


//
//  main.m
//  InvocationDemo
//

 

#import
#import "NimoReceiver.h"
 
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        //用Receiver的实例创建NSInvocation对象,并把Receiver的action作为选择器
        NimoReceiver *receiver = [[NimoReceiver alloc] init];
        NSString *name = @"Lee";
        NSString *gender = @"male";
        int age = 28;
        SEL sel = @selector(printWithName:gender:age:);
        NSMethodSignature *methodSignature = [[receiver class] instanceMethodSignatureForSelector:sel];
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
        [invocation setTarget:receiver];
        [invocation setSelector:sel];
        [invocation setArgument:&name atIndex:2];
        [invocation setArgument:&gender atIndex:3];
        [invocation setArgument:&age atIndex:4];
        [invocation retainArguments];
        [invocation invoke]; //通过调用NSInvocation对象的invoke方法,完成对Receiver中action的调用
        
        int returnValue = 0;
        [invocation getReturnValue:&returnValue];
        
        NSLog(@"returnValue: %d", returnValue);
    }
    return 0;
}


Running:

2015-08-14 13:37:44.162 InvocationDemo[1049:36632] My name is Lee, male, 28 years old.
2015-08-14 13:37:44.164 InvocationDemo[1049:36632] returnValue: 119

其实,单从类关系图中可以简单的看出,命令模式其实是把需求(Invoker)和具体实现(Receiver)通过命令层(Command)进行了解耦。具体实现过程根据不同的命令进行了区分。

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