设计模式

六大设计原则

单一职责

一个类则负责一件事。UIView只负责事件传递和响应。CALayer 视图展示

开闭原则

对修改关闭,对扩展开放

接口隔离

使用多个专门的协议,而不是一个庞大臃肿的协议。协议中的方法应尽量的少。eg. UITableViewDataSource 、UITableViewDelegate

依赖倒置原则

抽象不应该依赖于具体的实现,具体实现可以依赖抽象。eg. 上层只知道增删改查,不用知道底层用的是那种数据存储方案

里氏替换原则

父类可以被子类无缝替换,且原有功能不受影响 eg.KVO

迪米特法则

一个对象应当对其他对象有尽可能的少的了解。 高内聚、低耦合

五大设计模式

责任链

概念:为请求创建了一个对象响应者链。关键是:响应链。
场景:业务处理顺序A --> B --> C 变更为 C --> B --> A
代码实现

@class Business;

typedef void (^CompletionBlock)(BOOL handled);
typedef void (^ResultBlock)(Business *handler,BOOL handled);

@interface Business : NSObject

@property(nonatomic,strong)Business *nextBusiness;
@property(nonatomic,assign)int tag;

-(void)handle:(ResultBlock)result;

@end

@implementation Business


-(void)handle:(ResultBlock)result
{
    
    [self handleBusiness:^(BOOL handled) {
       
        if(handled){
            result(self,handled);
        }else{
            if(self.nextBusiness){
                [self.nextBusiness handle:result];
            }else{
                result(nil,NO);
            }
        }
        
    }];
}

-(void)handleBusiness:(CompletionBlock)completion
{
    if(_tag == 3){
        NSLog(@"tag = %d 处理",_tag);
        completion(YES);
    }else{
        NSLog(@"tag = %d 不处理",_tag);
        completion(NO);
    }
}


@end

- (void)viewDidLoad {
    [super viewDidLoad];
    Business *a = [[Business alloc]init];
    a.tag = 4;
    
    Business *b = [[Business alloc]init];
    b.tag = 5;
    
    Business *c = [[Business alloc]init];
    c.tag = 3;
    
    Business *d = [[Business alloc]init];
    d.tag = 1;
    
    a.nextBusiness = b;
    b.nextBusiness = c;
    c.nextBusiness = d;
    
    [a handle:^(Business *handler, BOOL handled) {
        
    }];
}
2018-04-23 14:52:56.793052+0800 TestDemo[2965:170447] tag = 4 不处理
2018-04-23 14:52:56.793195+0800 TestDemo[2965:170447] tag = 5 不处理
2018-04-23 14:52:56.793326+0800 TestDemo[2965:170447] tag = 3 处理

桥接模式

概念:抽象化与实现化解耦,使得二者可以独立变化
场景:列表根据三种不同数据源,显示三种不同的样式



解除列表和数据的耦合: ClassA带表列表抽象,ClassB代表数据数据抽象。ClassA拥有一个ClassB的实例对象。A1 B1等是具体实现。



代码实现
@interface BaseView : UIView

//桥接模式核心实现
@property(nonatomic,strong)BaseData *data;

//获取数据
-(void)handle;

@end

@implementation BaseView

-(void)handle
{
    [self.data fetchData];
}

@end

@interface BaseData : NSObject

-(void)fetchData;

@end

@implementation BaseData

-(void)fetchData
{
    //ovveride to subClass
}

@end

//在ViewDidLoad中,可以随意组合列表和数据
 BaseView  *view = [[View1 alloc]init];
 view.data  = [[Data2 alloc]init];
 [view handle];

适配器

概念:
对象适配器: 新的类包含一个旧的类的实例对象, 引入新的逻辑。将一个类的接口转换成客户希望的另外一个接口
类适配器:继承,通过子类引入新的逻辑
场景:旧的类使用好几年了没有变动。但是需求边了。要加入一些新的东西

@interface Target : NSObject

-(void)operation;

@end

@interface CoolTarget : NSObject

@property(nonatomic,strong)Target *target;  //被适配对象

-(void)request;


@end
@implementation CoolTarget

-(void)request
{
    //额外处理
    [self.target operation];
    //额外处理
}
@end
单例模式

概念:该类负责创建自己的对象,同时确保只有单个对象被创建

+(instancetype)sharedInstance
{
    static User *instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[super allocWithZone:NULL]init];  //注意点
    });
    return instance;
}

//必不可少
+(id)allocWithZone:(struct _NSZone *)zone
{
    return [self sharedInstance];
}

//必不可少
-(id)copy
{
    return self;
}
命令模式

概念:行为参数化,降低代码重合度。
场景:将一个请求封装成一个对象,并把命令传给响应的对象。eg .点赞,转发等这些常见需求


代码实现

@class Command;
typedef void (^CommandCompletionCallBack)(Command* cmd);

@interface Command : NSObject

@property(nonatomic,copy)CommandCompletionCallBack completion;

-(void)execute;
-(void)cancel;
-(void)done;

@end

@implementation Command

-(void)execute
{
    //override to subClass
    [self done];
}

-(void)cancel
{
    self.completion = nil;
}

-(void)done
{
    dispatch_async(dispatch_get_main_queue(), ^{
       
        if(_completion){
            _completion(self);
        }
        self.completion = nil;
        
    });
}

@end

@interface CommandManager : NSObject

@property(nonatomic,strong)NSMutableArray *arrayCommands;

+(instancetype)sharedInstance;

//执行命令
+(void)executeCommand:(Command *)cmd completion:(CommandCompletionCallBack)completion;

//取消命令
+(void)cancelCommand:(Command *)cmd;

@end

@implementation CommandManager


+(instancetype)sharedInstance
{
    static CommandManager *instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
     
        instance = [[super allocWithZone:NULL]init];
    });
    return instance;
}

-(id)init
{
    self = [super init];
    if(self){
        _arrayCommands = [NSMutableArray array];
    }
    return self;
}

//执行命令
+(void)executeCommand:(Command *)cmd completion:(CommandCompletionCallBack)completion
{
    
    if(cmd){
        //命令正在执行,则不处理
        if(![self _isExecutingCommand:cmd]){
            
            [[[CommandManager sharedInstance] arrayCommands] addObject:cmd];
            cmd.completion = completion;
            [cmd execute];
        }
    }

}

//取消命令
+(void)cancelCommand:(Command *)cmd
{
    if(cmd){
        [[[CommandManager sharedInstance] arrayCommands] removeObject:cmd];
        [cmd cancel];
    }
}

+(BOOL)_isExecutingCommand:(Command*)cmd
{
    NSArray *cmds = [[CommandManager sharedInstance] arrayCommands];
    for (Command *aCmd in  cmds) {
        
        if(cmd == aCmd){
            return YES;
        }
    }
    return NO;
}




@end

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