iOS奇思妙想之使用block替代通知（一）

前言

iOS开发中，很多情况下会使用到通知，通知的好处很多，但是也有很多坑点，一旦没有管理好，就会造成很多莫名其妙的bug。既然通知使用不当很容易出现问题，那有没有什么办法来避免？经过思考后，决定使用block回调的方式来实现通知，并且避免掉通知的弊端。

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原理

参考通知原理，采用单例全局管理，单例持有一个字典，字典中储存所有添加的block，在调用block的时候从字典中取出对应的block调用。通知原理参考—>>深入理解iOS NSNotification

1.完整的单例创建

单例创建需要考虑到各种初始化方法以及拷贝，还有线程安全。具体参考—>>完整单例模式写法

2.保证观察者生命周期不受单例影响

因为是单例持有的字典，就会造成block得不到释放，从而引起一系列问题。这里采用NSMapTable来储存block，NSMapTable使用强引用key，弱引用value，这样做的好处在于，当其中储存的对象销毁后，会自动从NSMapTable移除。使用NSMapTable可以保证生命周期不受单例影响。具体参考—>>Cocoa 集合类型：NSPointerArray，NSMapTable，NSHashTable

3.观察者和block绑定

为了使用简单，并且保证block生命周期和观察者一样，使用RunTime动态绑定，将block和观察者绑定起来。具体参考—>>iOS Runtime详解

4.保证一个对象只添加一次观察者

多次添加观察者会造成调用的时候响应多次，这里采用对象内存地址和标识符作为字典的key，保证一个对象只添加一次。

5.多线程安全

这里采用GCD信号量来保证线程安全，具体参考—>>GCD信号量

6.block循环引用

对于block循环引用，这里采用回调观察者替代self，保证不会循环引用，具体参考—>>Block循环引用详解

代码

上面讲解的就是整个项目实现的关键点，这里贴出具体代码。

CLActionManager.h实现代码

typedef NS_ENUM(NSUInteger, CLActionType) {
    CLActionColorChange,///<颜色变化
    CLActionTextChange,///<文字变化
    CLActionImageChange,///<图片变化
};


@interface CLActionManager : NSObject
/*
    所有响应block生命周期和观察者对象生命周期一样，一个对象多次添加同一类型或者同一标识符的观察者，只会添加最后一次，响应的block回掉会随着观察者对象销毁自动销毁，建议使用枚举管理所有标识符
 */


/**
 根据类型添加观察者
 
 @param observer 观察者
 @param actionType 响应类型
 @param block 数据回掉
 */
+ (void)addObserver:(id)observer actionType:(CLActionType)actionType mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block;

/**
 根据类型调用
 
 @param dictionary 数据
 @param actionType 响应类型
 */
+ (void)actionWithDictionary:(NSDictionary *)dictionary actionType:(CLActionType)actionType;

//------------------------------------字符串作为唯一标识符，内部已经处理，不会和上面枚举方式冲突-------------------------------------


/**
 根据标识符添加观察者

 @param observer 观察者
 @param identifier 标识
 @param mainThread 是否在主线程回掉
 @param block 数据回掉
 */
+ (void)addObserver:(id)observer identifier:(NSString *)identifier mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block;

/**
 根据标识符调用

 @param dictionary 数据
 @param identifier 标识符
 */
+ (void)actionWithDictionary:(NSDictionary *)dictionary identifier:(NSString *)identifier;

　　CLActionManager.m实现代码

//
//  CLActionManager.m
//  CLActionManager
//
//  Created by AUG on 2018/8/12.
//  Copyright © 2018年 JmoVxia. All rights reserved.
//

#import "CLActionManager.h"
#import <objc/message.h>

@interface CLActionManager ()

@property (nonatomic, strong) NSMapTable *observerMapTable;
@property (nonatomic, strong) NSMapTable *blockKeyMapTable;
@property (nonatomic, strong) NSMapTable *mainThreadKeyMapTable;
@property (nonatomic, strong) dispatch_semaphore_t semaphore;

@end

@implementation CLActionManager
//第1步: 存储唯一实例
static CLActionManager *_manager = nil;
//第2步: 分配内存空间时都会调用这个方法. 保证分配内存alloc时都相同.
+ (id)allocWithZone:(struct _NSZone __unused*)zone {
    return [self sharedManager];
}
//第3步: 保证init初始化时都相同
+ (instancetype)sharedManager {
    //调用dispatch_once保证在多线程中也只被实例化一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _manager = [[super allocWithZone:NULL] init];
    });
    return _manager;
}
- (id)init {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _manager = [super init];
        //弱引用value，强引用key
        self.observerMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        self.blockKeyMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        self.mainThreadKeyMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        //信号
        self.semaphore = dispatch_semaphore_create(0);
        dispatch_semaphore_signal(self.semaphore);
    });
    return _manager;
}
//第4步: 保证copy时都相同
- (id)copyWithZone:(NSZone __unused*)zone {
    return _manager;
}
//第五步: 保证mutableCopy时相同
- (id)mutableCopyWithZone:(NSZone __unused*)zone {
    return _manager;
}

+ (void)addObserver:(id)observer actionType:(CLActionType)actionType mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block {
    //增加信号保证线程安全
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //内存地址+key，使用内存地址保证一个对象只监听一次，key保证是同一类型
    NSString *key = [NSString stringWithFormat:@"%@-%@",[NSString stringWithFormat:@"%p",observer], [[self keyWithActionType:actionType] stringByAppendingString:@"-1"]];
    NSString *actionBlock = [key stringByAppendingString:@"-CLActionBlock-1"];
    NSString *actionMainThread = [key stringByAppendingString:@"-CLActionMainThread-1"];
    [[CLActionManager sharedManager].observerMapTable setObject:observer forKey:key];
    [[CLActionManager sharedManager].blockKeyMapTable setObject:actionBlock forKey:key];
    [[CLActionManager sharedManager].mainThreadKeyMapTable setObject:actionMainThread forKey:key];
    //动态设置block
    objc_setAssociatedObject(observer, CFBridgingRetain(actionBlock), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
    //动态设置是否主线程
    objc_setAssociatedObject(observer, CFBridgingRetain(actionMainThread), [NSNumber numberWithBool:mainThread], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    dispatch_semaphore_signal([CLActionManager sharedManager].semaphore);
}

+ (void)actionWithDictionary:(NSDictionary *)dictionary actionType:(CLActionType)actionType {
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //key数组
    NSArray<NSString *> *keyArray = [[[CLActionManager sharedManager].observerMapTable keyEnumerator] allObjects];
    //匹配出对应key
    NSString *identifier = [[self keyWithActionType:actionType] stringByAppendingString:@"-1"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF ENDSWITH %@",identifier];
    NSArray<NSString *> *array = [keyArray filteredArrayUsingPredicate:predicate];
    //遍历查找所有key
    for (NSString *key in array) {
        NSString *actionBlock = [[CLActionManager sharedManager].blockKeyMapTable objectForKey:key];
        NSString *actionMainThread = [[CLActionManager sharedManager].mainThreadKeyMapTable objectForKey:key];
        //找出对应类型的观察者
        id observer = [[CLActionManager sharedManager].observerMapTable objectForKey:key];
        //取出block
        void(^block)(id observer, NSDictionary *dictionary) = objc_getAssociatedObject(observer, CFBridgingRetain(actionBlock));
        BOOL mainThread = [(NSNumber *)objc_getAssociatedObject(observer, CFBridgingRetain(actionMainThread)) boolValue];
        //block存在并且是对应方法添加，调用block
        if (block) {
            if (mainThread) {
                //主线程
                dispatch_async(dispatch_get_main_queue(), ^{
                    block(observer, dictionary);
                });
            }else {
                //子线程
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                    block(observer, dictionary);
                });
            }
        }
    }
    dispatch_semaphore_signal([CLActionManager sharedManager].semaphore);
}

+ (NSString *)keyWithActionType:(CLActionType)actionType {
    NSString *key;
    switch (actionType) {
        case CLActionTextChange:
            key = @"CLActionTextChange";
            break;
        case CLActionColorChange:
            key = @"CLActionColorChange";
            break;
        case CLActionImageChange:
            key = @"CLActionImageChange";
            break;
    }
    return key;
}

+ (void)addObserver:(id)observer identifier:(NSString *)identifier mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block {
    //增加信号保证线程安全
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //内存地址+key，使用内存地址保证一个对象只监听一次，key保证是同一类型
    NSString *key = [NSString stringWithFormat:@"%@-%@",[NSString stringWithFormat:@"%p",observer], [identifier stringByAppendingString:@"-0"]];
    NSString *actionBlock = [key stringByAppendingString:@"-CLActionBlock-0"];
    NSString *actionMainThread = [key stringByAppendingString:@"-CLActionMainThread-0"];
    [[CLActionManager sharedManager].observerMapTable setObject:observer forKey:key];
    [[CLActionManager sharedManager].blockKeyMapTable setObject:actionBlock forKey:key];
    [[CLActionManager sharedManager].mainThreadKeyMapTable setObject:actionMainThread forKey:key];
    //动态设置block
    objc_setAssociatedObject(observer, CFBridgingRetain(actionBlock), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
    //动态设置是否主线程
    objc_setAssociatedObject(observer, CFBridgingRetain(actionMainThread), [NSNumber numberWithBool:mainThread], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    dispatch_semaphore_signal([CLActionManager sharedManager].semaphore);
}

+ (void)actionWithDictionary:(NSDictionary *)dictionary identifier:(NSString *)identifier {
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //key数组
    NSArray<NSString *> *keyArray = [[[CLActionManager sharedManager].observerMapTable keyEnumerator] allObjects];
    //匹配出对应key
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF ENDSWITH %@",[identifier stringByAppendingString:@"-0"]];
    NSArray<NSString *> *array = [keyArray filteredArrayUsingPredicate:predicate];
    //遍历查找所有key
    for (NSString *key in array) {
        NSString *actionBlock = [[CLActionManager sharedManager].blockKeyMapTable objectForKey:key];
        NSString *actionMainThread = [[CLActionManager sharedManager].mainThreadKeyMapTable objectForKey:key];
        //找出对应类型的观察者
        id observer = [[CLActionManager sharedManager].observerMapTable objectForKey:key];
        //取出block
        void(^block)(id observer, NSDictionary *dictionary) = objc_getAssociatedObject(observer, CFBridgingRetain(actionBlock));
        BOOL mainThread = [(NSNumber *)objc_getAssociatedObject(observer, CFBridgingRetain(actionMainThread)) boolValue];
        //block存在并且是对应方法添加，调用block
        if (block) {
            if (mainThread) {
                //主线程
                dispatch_async(dispatch_get_main_queue(), ^{
                    block(observer, dictionary);
                });
            }else {
                //子线程
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                    block(observer, dictionary);
                });
            }
        }
    }
    dispatch_semaphore_signal([CLActionManager sharedManager].semaphore);
}

@end

　　测试结果

测试效果已经达到我们需要的效果，看一下打印结果，所有的观察者的生命周期都没有受到影响、

AViewController收到颜色变化,当前线程<NSThread: 0x608000263000>{number = 1, name = main}
BViewController收到颜色变化，当前线程<NSThread: 0x608000263000>{number = 1, name = main}
ViewController收到颜色变化,当前线程<NSThread: 0x608000263000>{number = 1, name = main}
收到其他地方头像变化了,当前线程--<NSThread: 0x608000263000>{number = 1, name = main}
收到其他地方头像变化了,当前线程--<NSThread: 0x608000263000>{number = 1, name = main}
++++++++++>>>>BViewController销毁了
头像View销毁了----0x7fbee1d08fb0
--------->>>>AViewController销毁了
头像View销毁了----0x7fbee1e1a3b0

　　

总结

以上是根据通知原理来自己实现的自定义响应类，希望能够给大家帮助，demo地址—>>CLActionManager

原文作者：季末微夏
原文地址：https://www.jianshu.com/p/00c558c72ae7