iOS奇思妙想之使用block替代通知

JmoVxia發表於2018-08-16
iOSBloC

前言

iOS開發中，很多情況下會使用到通知，通知的好處很多，但是也有很多坑點，一旦沒有管理好，就會造成很多莫名其妙的bug。既然通知使用不當很容易出現問題，那有沒有什麼辦法來避免？經過思考後，決定使用block回撥的方式來實現通知，並且避免掉通知的弊端。

原理

參考通知原理，採用單例全域性管理，單例持有一個字典，字典中儲存所有新增的block，在呼叫block的時候從字典中取出對應的block呼叫。通知原理參考--->>深入理解iOS NSNotification

1.完整的單例建立

單例建立需要考慮到各種初始化方法以及拷貝，還有執行緒安全。具體參考--->>完整單例模式寫法

2.保證觀察者生命週期不受單例影響

因為是單例持有的字典，就會造成block得不到釋放，從而引起一系列問題。這裡採用NSMapTable來儲存block，NSMapTable使用強引用key，弱引用value，這樣做的好處在於，當其中儲存的物件銷燬後，會自動從NSMapTable移除。使用NSMapTable可以保證生命週期不受單例影響。具體參考--->>Cocoa 集合型別：NSPointerArray，NSMapTable，NSHashTable

3.觀察者和block繫結

為了使用簡單，並且保證block生命週期和觀察者一樣，使用RunTime動態繫結，將block和觀察者繫結起來。具體參考--->>iOS Runtime詳解

4.保證一個物件只新增一次觀察者

多次新增觀察者會造成呼叫的時候響應多次，這裡採用物件記憶體地址和識別符號作為字典的key，保證一個物件只新增一次。

5.多執行緒安全

這裡採用GCD訊號量來保證執行緒安全，具體參考--->>GCD訊號量

6.block迴圈引用

對於block迴圈引用，這裡採用回撥觀察者替代self，保證不會迴圈引用，具體參考--->>Block迴圈引用詳解

程式碼

上面講解的就是整個專案實現的關鍵點，這裡貼出具體程式碼。

CLActionManager.h實現程式碼

typedef NS_ENUM(NSUInteger, CLActionType) {
    CLActionColorChange,///<顏色變化
    CLActionTextChange,///<文字變化
    CLActionImageChange,///<圖片變化
};


@interface CLActionManager : NSObject
/*
    所有響應block生命週期和觀察者物件生命週期一樣，一個物件多次新增同一型別或者同一識別符號的觀察者，只會新增最後一次，響應的block回掉會隨著觀察者物件銷燬自動銷燬，建議使用列舉管理所有識別符號
 */


/**
 根據型別新增觀察者
 
 @param observer 觀察者
 @param actionType 響應型別
 @param block 資料回掉
 */
+ (void)addObserver:(id)observer actionType:(CLActionType)actionType mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block;

/**
 根據型別呼叫
 
 @param dictionary 資料
 @param actionType 響應型別
 */
+ (void)actionWithDictionary:(NSDictionary *)dictionary actionType:(CLActionType)actionType;

//------------------------------------字串作為唯一識別符號，內部已經處理，不會和上面列舉方式衝突-------------------------------------


/**
 根據識別符號新增觀察者

 @param observer 觀察者
 @param identifier 標識
 @param mainThread 是否在主執行緒回掉
 @param block 資料回掉
 */
+ (void)addObserver:(id)observer identifier:(NSString *)identifier mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block;

/**
 根據識別符號呼叫

 @param dictionary 資料
 @param identifier 識別符號
 */
+ (void)actionWithDictionary:(NSDictionary *)dictionary identifier:(NSString *)identifier;



複製程式碼

CLActionManager.m實現程式碼


#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: 儲存唯一例項
static CLActionManager *_manager = nil;
//第2步: 分配記憶體空間時都會呼叫這個方法. 保證分配記憶體alloc時都相同.
+ (id)allocWithZone:(struct _NSZone *)zone {
    //呼叫dispatch_once保證在多執行緒中也只被例項化一次
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _manager = [super allocWithZone:zone];
    });
    return _manager;
}
//第3步: 保證init初始化時都相同
+ (instancetype)sharedManager {
    return [[self alloc] init];
}
- (id)init {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _manager = [super init];
        //弱引用value，強引用key
        self.observerMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        self.blockKeyMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        self.mainThreadKeyMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
        //訊號
        self.semaphore = dispatch_semaphore_create(0);
        dispatch_semaphore_signal(self.semaphore);
    });
    return _manager;
}
//第4步: 保證copy時都相同
- (id)copyWithZone:(NSZone __unused*)zone {
    return _manager;
}
//第五步: 保證mutableCopy時相同
- (id)mutableCopyWithZone:(NSZone __unused*)zone {
    return _manager;
}

+ (void)addObserver:(id)observer actionType:(CLActionType)actionType mainThread:(BOOL)mainThread block:(void(^)(id observer, NSDictionary *dictionary))block {
    //增加訊號保證執行緒安全
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //記憶體地址+key，使用記憶體地址保證一個物件只監聽一次，key保證是同一型別
    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];
    //動態設定block
    objc_setAssociatedObject(observer, CFBridgingRetain(actionBlock), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
    //動態設定是否主執行緒
    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陣列
    NSArray<NSString *> *keyArray = [[[CLActionManager sharedManager].observerMapTable keyEnumerator] allObjects];
    //匹配出對應key
    NSString *identifier = [[self keyWithActionType:actionType] stringByAppendingString:@"-1"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS %@",identifier];
    NSArray<NSString *> *array = [keyArray filteredArrayUsingPredicate:predicate];
    //遍歷查詢所有key
    for (NSString *key in array) {
        NSString *actionBlock = [[CLActionManager sharedManager].blockKeyMapTable objectForKey:key];
        NSString *actionMainThread = [[CLActionManager sharedManager].mainThreadKeyMapTable objectForKey:key];
        //找出對應型別的觀察者
        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存在並且是對應方法新增，呼叫block
        if (block) {
            if (mainThread) {
                //主執行緒
                dispatch_async(dispatch_get_main_queue(), ^{
                    block(observer, dictionary);
                });
            }else {
                //子執行緒
                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 {
    //增加訊號保證執行緒安全
    dispatch_semaphore_wait([CLActionManager sharedManager].semaphore, DISPATCH_TIME_FOREVER);
    //記憶體地址+key，使用記憶體地址保證一個物件只監聽一次，key保證是同一型別
    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];
    //動態設定block
    objc_setAssociatedObject(observer, CFBridgingRetain(actionBlock), block, OBJC_ASSOCIATION_COPY_NONATOMIC);
    //動態設定是否主執行緒
    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陣列
    NSArray<NSString *> *keyArray = [[[CLActionManager sharedManager].observerMapTable keyEnumerator] allObjects];
    //匹配出對應key
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS %@",[identifier stringByAppendingString:@"-0"]];
    NSArray<NSString *> *array = [keyArray filteredArrayUsingPredicate:predicate];
    //遍歷查詢所有key
    for (NSString *key in array) {
        NSString *actionBlock = [[CLActionManager sharedManager].blockKeyMapTable objectForKey:key];
        NSString *actionMainThread = [[CLActionManager sharedManager].mainThreadKeyMapTable objectForKey:key];
        //找出對應型別的觀察者
        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存在並且是對應方法新增，呼叫block
        if (block) {
            if (mainThread) {
                //主執行緒
                dispatch_async(dispatch_get_main_queue(), ^{
                    block(observer, dictionary);
                });
            }else {
                //子執行緒
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                    block(observer, dictionary);
                });
            }
        }
    }
    dispatch_semaphore_signal([CLActionManager sharedManager].semaphore);
}

@end

複製程式碼

測試結果

效果圖

測試效果已經達到我們需要的效果，看一下列印結果，所有的觀察者的生命週期都沒有受到影響

AViewController收到顏色變化,當前執行緒<NSThread: 0x608000263000>{number = 1, name = main}
BViewController收到顏色變化，當前執行緒<NSThread: 0x608000263000>{number = 1, name = main}
ViewController收到顏色變化,當前執行緒<NSThread: 0x608000263000>{number = 1, name = main}
收到其他地方頭像變化了,當前執行緒--<NSThread: 0x608000263000>{number = 1, name = main}
收到其他地方頭像變化了,當前執行緒--<NSThread: 0x608000263000>{number = 1, name = main}
++++++++++>>>>BViewController銷燬了
頭像View銷燬了----0x7fbee1d08fb0
--------->>>>AViewController銷燬了
頭像View銷燬了----0x7fbee1e1a3b0
複製程式碼

總結

以上是根據通知原理來自己實現的自定義響應類，希望能夠給大家幫助，demo地址--->>CLActionManager

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