iOS架構設計模式之命令模式

一 基本概念

Demo地址

  1. 定義：它屬于行為型模式，將一個請求封裝成一個對象，從而讓你使用不同的請求把客戶端參數(shù)化，請求以命令的形式包裹在對象中，并傳給調用對象。調用對象尋找可以處理該命令的合適的對象，并把該命令傳給相應的對象，該對象執(zhí)行命令。降低耦合度。
  2. 使用場景：應用程序支持撤銷和恢復；記錄請求日志，當系統(tǒng)故障時可以重新被執(zhí)行；想用對象參數(shù)化一個動作以執(zhí)行操作并且用不同命令來替換回調函數(shù)。

  3. 角色劃分：
    接收者-> Reciever
    命令接口-> Command（CommandProtocol協(xié)議）
    具體命令-> ConcrateCommand
    請求者-> Invoker：持有命令對象的引用 然后執(zhí)行對象的命令
    Client類：最終的客戶端調用類。


二 基礎案例

  1. CommandProtocol
//命令接口-協(xié)議
@protocol Meryin_CommandProtocol<NSObject>
//操作->具體實現(xiàn)方法
-(void)execute;
@end
  1. 接收者Reciever實現(xiàn)具體方法功能
//接收者
@interface Meryin_Reciever : NSObject
//具體方法
-(void)start;
@end

@implementation Meryin_Reciever
-(void)start{
    NSLog(@"接收者實現(xiàn)具體方法的功能");
}
@end
  1. ConcrateCommand 遵守協(xié)議，持有接收者，實現(xiàn)協(xié)議具體方法,調用具體邏輯
//具體命令-> ConcrateCommand
//遵守協(xié)議，實現(xiàn)協(xié)議具體方法
@interface Meryin_ConcrateCommand : NSObject<meryin_CommandProtocol>
- (instancetype)initWithReciever:(Meryin_Reciever *)reciever;
@end

@interface Meryin_ConcrateCommand()
@property(nonatomic, strong) Meryin_Reciever* reciever;
@end
@implementation Meryin_ConcrateCommand
- (instancetype)initWithReciever:(Meryin_Reciever *)reciever
{
    self = [super init];
    if (self) {
        self.reciever = reciever;
    }
    return self;
}

-(void)execute{
    [self.reciever start];
}
@end
  1. Invoker 請求者，持有ConcrateCommand的引用，執(zhí)行ConcrateCommand遵守協(xié)議的方法；保存操作記錄支持回退撤銷。

@interface Meryin_Invoker()
@property (nonatomic,strong)NSMutableArray  *commands;
@property (nonatomic,strong)Meryin_Reciever  *reciever;
@property(nonatomic, strong)id <Meryin_CommandProtocol> command;
@end

@implementation Meryin_Invoker

- (instancetype)initWith:(Meryin_ConcrateCommand *)command reciever:(Meryin_Reciever *)reciver
{
    self = [super init];
    if (self) {
        self.command = command;
        self.reciever = reciver;
        self.commands = [NSMutableArray array];
    }
    return self;
}

-(void)toStart{
    [self.command execute];
    [self.commands addObject:[[Meryin_ConcrateCommand alloc]initWithReciever:self.reciever] ];
}

//支持撤銷
//撤銷最后一個命令
- (void)undoLastOne{
    if (self.commands.count >0) {
        NSLog(@"撤銷--%lu",self.commands.count-1);
        //撤銷
        [[self.commands lastObject] execute];
        //移除
        [self.commands removeLastObject];
    }
}
  1. Client 最后調用
 //創(chuàng)建接收者
        Meryin_Reciever  *reciver = [[Meryin_Reciever alloc]init];
        //創(chuàng)建命令(分離)->解藕和
        Meryin_ConcrateCommand *command = [[Meryin_ConcrateCommand alloc]initWithReciever:reciver];
        //創(chuàng)建請求者
        Meryin_Invoker  *invoker = [[Meryin_Invoker alloc]initWith:command reciever:reciver];
        [invoker toStart];
        [invoker toStart];
        [invoker undoLastOne];

三 基礎命令模式的一步步優(yōu)化

1. 動態(tài)命令

以上創(chuàng)建的命令模式，當命令過多時，類就會太多，不好管理，如果使用動態(tài)調用，用Block回調，不需要新建各種命令類，用Block實現(xiàn)一個命令類里面可以動態(tài)創(chuàng)建多個命令。

  • 創(chuàng)建動態(tài)命令類DynamicCommand，持有block,可以動態(tài)創(chuàng)建命令實現(xiàn)接收者的各種方法。
typedef void(^dynamicBlcok)(Meryin_Reciever *);
//解決方法：用block實現(xiàn)
@interface DynamicCommand : NSObject<meryin_CommandProtocol>
- (instancetype)initWith:(Meryin_Reciever *)reciver block:(dynamicBlcok)block;
//創(chuàng)建命令
+(id<meryin_CommandProtocol>)createCommand:(Meryin_Reciever *)reciver block:(dynamicBlcok)block;
@end

@interface DynamicCommand()
@property(nonatomic, strong) Meryin_Reciever* reciever;
@property(nonatomic, copy) dynamicBlcok  block;
@end

@implementation DynamicCommand
- (instancetype)initWith:(Meryin_Reciever *)reciver block:(dynamicBlcok)block
{
    self = [super init];
    if (self) {
        self.reciever = reciver;
        self.block = block;
    }
    return self;
}
- (void)execute{
    if (self.block) {
        self.block(self.reciever);
    }
}
//創(chuàng)建命令
+(id<meryin_CommandProtocol>)createCommand:(Meryin_Reciever *)reciver block:(dynamicBlcok)block{
    return [[DynamicCommand alloc]initWith:reciver block:block];
}
  • 動態(tài)命令的請求者，動態(tài)添加命令，實現(xiàn)接收者方法的回調
@interface DynamicCommandManager()
@property (nonatomic,strong)NSMutableArray  *commands;
@property (nonatomic,strong)Meryin_Reciever  *reciever;
@end

@implementation DynamicCommandManager

- (instancetype)initWith:(Meryin_Reciever *)reciver{
    self = [super init];
    if (self) {
        self.reciever = reciver;
        self.commands = [NSMutableArray array];
    }
    return self;
}
-(void)toStart{
    [self addCommand:@"start"];
    [ self.reciever start];
}
- (void)toEnd{
    [self addCommand:@"end"];
    [self.reciever end];
}
- (void)addCommand:(NSString *)methodName{
    //動態(tài)添加命令
   DynamicCommand *command =[DynamicCommand createCommand:self.reciever block:^(Meryin_Reciever *block) {
   SEL method = NSSelectorFromString(methodName);
        //執(zhí)行回調
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        [block performSelector:method];
#pragma clang diagnostic pop
    }];
    [self.commands addObject:command];
}
//撤銷最后一個命令
- (void)undoLastOne{
    if (self.commands.count >0) {
        NSLog(@"撤銷--%lu",self.commands.count-1);
        //撤銷
        [[self.commands lastObject] execute];
        //移除
        [self.commands removeLastObject];
    }
}
//撤銷所有
- (void)undoAll{
    if (self.commands.count >0) {
        NSLog(@"撤銷所有");
        //撤銷
        for (id <meryin_CommandProtocol> command in self.commands) {
            [command execute];
        }
        //移除
        [self.commands removeAllObjects];
    }
}
  • Client客戶端調用
//動態(tài)命令
        Meryin_Reciever  *reciver1 = [[Meryin_Reciever alloc]init];
        DynamicCommandManager  *manager1 = [[DynamicCommandManager alloc]initWith:reciver1];
        [manager1 toEnd];
        [manager1 toStart];
        [manager1 toStart];
        [manager1 toEnd];
        [manager1 undoByIndex:2];

命令模式并不去實現(xiàn)具體業(yè)務邏輯，只用于記錄撤銷等。具體撤銷邏輯由Client決定，命令模式只是保存操作。

2. 復合命令

執(zhí)行多個命令叫復合命令

  • 新建復合命令WrapperCommand，遵守協(xié)議
@interface WrapperCommand : NSObject<meryin_CommandProtocol>
- (instancetype)initWith:(NSMutableArray *)commands;
@end

@interface WrapperCommand()
@property(nonatomic, strong) NSMutableArray* commands;
@end
@implementation WrapperCommand
- (instancetype)initWith:(NSMutableArray *)commands
{
    self = [super init];
    if (self) {
        self.commands = commands;
    }
    return self;
}
- (void)execute{
    for (id<meryin_CommandProtocol> item in self.commands) {
        [item execute];
    }
}
  • 請求者-復合命令管理器WrapperCommandManager
    跟動態(tài)命令DynamicCommandManager類似，只有撤銷所有的方法不一樣
//撤銷所有
- (void)undoAll{
    if (self.commands.count >0) {
        NSLog(@"撤銷所有");
        //撤銷
        for (id <meryin_CommandProtocol> command in self.commands) {
            [command execute];
        }
        //移除
        [self.commands removeAllObjects];
    }
}
3. 泛型命令

在定義的時候不需要指定類型，在使用的時候指定類型。c++里叫模版。

  • 新建GenericsCommand泛型命令,接收者是動態(tài)的，可以持有任何接收者
//可以接受所有接收者
//T任意類型的標記
@interface GenericsCommand<T> : NSObject<meryin_CommandProtocol>
- (instancetype)initWith:(T)reciver block:(void(^)(T))commandBlock;
+(id<meryin_CommandProtocol>)createCommand:(T)reciver block:(void (^)(T))block;
@end

@interface GenericsCommand<T>()
@property(nonatomic, strong) T reciever;
@property(nonatomic, copy) void(^block)(T);
@end
@implementation GenericsCommand

//id 指向泛型類型的引用
- (instancetype)initWith:(id)reciver block:(void(^)(id))commandBlock
{
    self = [super init];
    if (self) {
        self.reciever = reciver;
        self.block = commandBlock;
    }
    return self;
}
//創(chuàng)建命令
+(id<meryin_CommandProtocol>)createCommand:(id)reciver block:(void (^)(id))block{
    return [[GenericsCommand alloc]initWith:reciver block:block];
}
- (void)execute{
    if (self.block) {
        self.block(self.reciever);
    }
}
  • 泛型命令管理器,用泛型命令創(chuàng)建命令集合
@implementation GenericsCommandManager
- (instancetype)initWith:(Meryin_Reciever *)reciver{
    self = [super init];
    if (self) {
        self.reciever = reciver;
        self.commands = [NSMutableArray array];
    }
    return self;
}
-(void)toStart{
    [self addCommand:@"start"];
    [ self.reciever start];
}
- (void)toEnd{
    [self addCommand:@"end"];
    [self.reciever end];
}
- (void)addCommand:(NSString *)methodName{
    //動態(tài)添加命令
   GenericsCommand *command =[GenericsCommand createCommand:self.reciever block:^(Meryin_Reciever *block) {
    SEL method = NSSelectorFromString(methodName);
        //執(zhí)行回調
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        [block performSelector:method];
#pragma clang diagnostic pop
    }];
    [self.commands addObject:command];
}
//撤銷所有
- (void)undoAll{
    if (self.commands.count >0) {
        NSLog(@"撤銷所有");
        //撤銷
        WrapperCommand *commands = [[WrapperCommand alloc]initWith:self.commands];
        [commands execute];
        //移除
        [self.commands removeAllObjects];
    }
}
4. 并發(fā)處理
- (void)addCommand:(NSString *)methodName{
    dispatch_sync(self.queue, ^{
        //動態(tài)添加命令
        GenericsCommand *commnad = [GenericsCommand createCommand:self.reciever block:^(Meryin_Reciever *block) {
        SEL method = NSSelectorFromString(methodName);
            //執(zhí)行回調
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
            [block performSelector:method];
#pragma clang diagnostic pop
        }];
        [self.commands addObject:commnad];
    });
}
5. 命令接口 Command用block

之前CommandProtocol用的是協(xié)議，現(xiàn)在用block,直接用管理器,隊列里保存的是block

- (void)addCommand:(NSString *)methodName{
    dispatch_sync(self.queue, ^{
        SEL method = NSSelectorFromString(methodName);
        //動態(tài)添加命令
        blcokCommand block = ^(Meryin_Reciever *reciver){
            //執(zhí)行回調
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
            [reciver performSelector:method];
#pragma clang diagnostic pop
        };
        [self.commands addObject:block];
       
    });
}
//撤銷第幾個 從0開始
- (void)undoByIndex:(NSInteger )index{
    if (self.commands.count >0 && self.commands.count > index) {
        NSLog(@"撤銷--%lu",index);
        //撤銷
        blcokCommand commandBlock= [self.commands objectAtIndex:index] ;
         commandBlock(self.reciever);
        //移除
        [self.commands removeObjectAtIndex:index];
    }
}

四 命令模式應用場景-購物車商品的添加刪減

命令模式的撤銷和其他業(yè)務邏輯分開，商品的增加和刪減可以和其他業(yè)務邏輯分開，可以減少controller的代碼量
分析角色：命令接口CommandProtocol，具體命令GenericsCommand，接收者ShoppingRecevier，請求者GenericsCommandManager
實際案例中命令保存時成對出現(xiàn),比如減少購物車商品的撤銷其實就是增加購物車商品

- (void)addGood:(NSString *)value withMode:(GoodsMode*)goods{
    [self addCommand:@"reduceGood:withMode:" value:value model:goods];
     [self.reciever addGood:value withMode:goods];
}
- (void)reduceGood:(NSString *)value withMode:(GoodsMode*)goods{
    [self addCommand:@"addGood:withMode:" value:value model:goods];
    [self.reciever reduceGood:value withMode:goods];
}
//保存命令
- (void)addCommand:(NSString *)methodName value:(NSString *)value model:(GoodsMode*)goods{
  
    //動態(tài)添加命令
   [self.commands addObject: [GenericsCommand createCommand:self.reciever block:^(ShoppingRecevier *reciver) {
          SEL method = NSSelectorFromString(methodName);
        //執(zhí)行回調
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
        if (reciver && method){
            [reciver performSelector:method withObject:value withObject:goods];
        }
#pragma clang diagnostic pop
   }]];
}
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