iOS设计模式之代理模式

2024-05-09 本文已影响0人点滴86

代理模式的原理解析

代理模式（Proxy Design Pattern）在不改变原始类代码的情况下，通过引入代理类来给原始类附加功能。

@interface DMRequestInfo : NSObject

@property (nonatomic, strong) NSString *keyWord;

@property (nonatomic, assign) NSTimeInterval responseTime;

@property (nonatomic, assign) NSTimeInterval startTime;

@end

@implementation DMRequestInfo

@end

@interface DMMetricsCollector : NSObject

- (void)recordRequest:(DMRequestInfo *)requestInfo;

@end

@implementation DMMetricsCollector

- (void)recordRequest:(DMRequestInfo *)requestInfo
{
    
}

@end

@interface DMUserController : NSObject

- (instancetype)initWithMetricsCollector:(DMMetricsCollector *)metricsCollector;

- (void)userLogin:(NSString *)telephone password:(NSString *)password;

- (void)userRegister:(NSString *)telephone password:(NSString *)password;

@end

@interface DMUserController ()

@property (nonatomic, strong) DMMetricsCollector *metricsCollector;

@end

@implementation DMUserController

- (instancetype)initWithMetricsCollector:(DMMetricsCollector *)metricsCollector
{
    if (self = [super init]) {
        self.metricsCollector = metricsCollector;
    }
    
    return self;
}

- (void)userLogin:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    // 省略登录逻辑
    
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"login";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

- (void)userRegister:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    // 省略注册逻辑
    
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"register";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

@end

上面的写法有两个问题：

1.性能计数器框架代码侵入到业务代码中，跟业务代码高度耦合。如果未来需要替换这个框架，那替换成本会比较大。
2.收集接口请求的代码跟业务代码无关，本就不应该放到一个类中。业务类最好职责更加单一，只聚焦业务处理。

为了将框架代码和业务代码解耦，代理模式就派上用场了。代理类DMUserControllerProxy和原始类DMUserController实现相同的接口DMUserControllerDelegate。DMUserController类只负责业务功能。代理类DMUserControllerProxy负责在业务代码执行前后附加其他逻辑代码，并通过委托的方式调用原始类类执行业务代码。具体的代码实现如下：

@protocol DMUserControllerDelegate <NSObject>

- (void)userLogin:(NSString *)telephone password:(NSString *)password;

- (void)userRegister:(NSString *)telephone password:(NSString *)password;

@end

@interface DMUserController : NSObject <DMUserControllerDelegate>

@end

@implementation DMUserController

#pragma mark - DMUserControllerDelegate method
- (void)userLogin:(NSString *)telephone password:(NSString *)password
{
    // 省略登录逻辑
}

- (void)userRegister:(NSString *)telephone password:(NSString *)password
{
    // 省略注册逻辑
}

@end

@interface DMUserControllerProxy : NSObject <DMUserControllerDelegate>

- (instancetype)initWithUserController:(DMUserController *)userController;

@end

@interface DMUserControllerProxy ()

@property (nonatomic, strong) DMUserController *userController;

@property (nonatomic, strong) DMMetricsCollector *metricsCollector;

@end

@implementation DMUserControllerProxy

- (instancetype)initWithUserController:(DMUserController *)userController
{
    if (self = [super init]) {
        self.userController = userController;
        self.metricsCollector = [[DMMetricsCollector alloc] init];
    }
    
    return self;
}

#pragma mark - DMUserControllerDelegate method
- (void)userLogin:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    [self.userController userLogin:telephone password:password];
    
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"login";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

- (void)userRegister:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    
    [self.userController userRegister:telephone password:password];
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"register";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

@end

使用代码示例如下：

id<DMUserControllerDelegate> userController = [[DMUserControllerProxy alloc] initWithUserController:[[DMUserController alloc] init]];
    
[userController userLogin:@"159****3273" password:@"123456"];
[userController userRegister:@"159****3273" password:@"123456"];

参照基于接口而非实现编程的设计思想，将原始类对象替换为代理类对象的时候，为了让代码改动尽量少，在刚刚的代理模式的代码实现中，代理类和原始类需要实现相同的接口。但是，如果原始类并没有定义接口，并且原始类代码并不是我们开发维护的（比如它来自一个第三方的类库），我们也没办法直接修改原始类，给它重新定义一个接口。在这种情况下，该如何实现代理模式呢？
对于这种外部类的扩展，一般都是采用继承的方式。让代理类继承原始类，然后扩展附加功能。具体代码如下：

@interface DMUserControllerProxy : DMUserController

@end

@interface DMUserControllerProxy ()

@property (nonatomic, strong) DMMetricsCollector *metricsCollector;

@end

@implementation DMUserControllerProxy

- (instancetype)init {
    if (self = [super init]) {
        self.metricsCollector = [[DMMetricsCollector alloc] init];
    }
    
    return self;
}

- (void)userLogin:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    [super userLogin:telephone password:password];
    
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"login";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

- (void)userRegister:(NSString *)telephone password:(NSString *)password
{
    NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
    
    [super userRegister:telephone password:password];
    NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
    NSTimeInterval responseTime = endTime - startTime;
    DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    requestInfo.keyWord = @"register";
    requestInfo.responseTime = responseTime;
    requestInfo.startTime = startTime;
    
    [self.metricsCollector recordRequest:requestInfo];
}

@end

动态代理的原理解析

刚刚的代码实现还是有点问题：

1.需要在代理类中，将原始类中的所有方法，都重新实现一遍，并且为每个方法都附加相似的代码逻辑。
2.如果要添加的附加功能的类不止一个，需要针对每一个类都创建一个代理类。

如果有50个要添加附加功能的原始类，那就要创建50个对应的代理类。这会导致项目中类的个数成倍增加，增加了代码的维护成本。并且，每个代理类中的代码都有点像模板式的“重复”代码，也增加了不必要的开发成本。这个问题怎么解决呢？
可以使用动态代理来解决这个问题。所谓动态代理就是不事先为每个原始类编写代理类，而是在运行的时候，动态地创建原始类对应的代理类，然后再系统中用代理类替换掉原始类。

@interface DMMetricsCollectorProxy : NSProxy

- (instancetype)initWithTarget:(id)target;

+ (instancetype)proxyWithTarget:(id)target;

@end

@interface DMMetricsCollectorProxy ()

@property (nonatomic, weak) id target;

@property (nonatomic, strong) DMMetricsCollector *metricsCollector;

@end

@implementation DMMetricsCollectorProxy

- (instancetype)initWithTarget:(id)target
{
    self.target = target;
    self.metricsCollector = [[DMMetricsCollector alloc] init];
    return self;
}

+ (instancetype)proxyWithTarget:(id)target
{
    return [[DMMetricsCollectorProxy alloc] initWithTarget:target];
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
    SEL sel = invocation.selector;
    if (self.target && [self.target respondsToSelector:sel]) {
        NSTimeInterval startTime = [[NSDate date] timeIntervalSince1970];
        
        [invocation invokeWithTarget:self.target];
        
        NSTimeInterval endTime = [[NSDate date] timeIntervalSince1970];
        NSTimeInterval responseTime = endTime - startTime;
        DMRequestInfo *requestInfo = [[DMRequestInfo alloc] init];
    
        NSString *className = NSStringFromClass([self.target class]);
        NSString *selectorName = NSStringFromSelector(sel);
        requestInfo.keyWord = [NSString stringWithFormat:@"%@%@", className, selectorName];
        requestInfo.responseTime = responseTime;
        requestInfo.startTime = startTime;
        
        [self.metricsCollector recordRequest:requestInfo];
    }
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
    if (self.target && [self.target respondsToSelector:selector]) {
        return [self.target methodSignatureForSelector:selector];
    } else {
        return nil;
    }
}

@end

使用的代码如下

DMUserController *tmpUser = [[DMUserController alloc] init];
id<DMUserControllerDelegate> tmpProxy = (id<DMUserControllerDelegate>)[DMMetricsCollectorProxy proxyWithTarget:tmpUser];
[tmpProxy userLogin:@"159****3273" password:@"123456"];

iOS设计模式之代理模式

代理模式的原理解析

动态代理的原理解析

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