ReactiveCocoa中潜在的内存泄漏及解决方案

- (void)viewDidLoad
{
    [super viewDidLoad];
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) { //1
        MTModel *model = [[MTModel alloc] init]; // MTModel有一个名为的title的属性
        [subscriber sendNext:model];
        [subscriber sendCompleted];
        return nil;
    }];
    self.flattenMapSignal = [signal flattenMap:^RACStream *(MTModel *model) { //2
        return RACObserve(model, title);
    }];
    [self.flattenMapSignal subscribeNext:^(id x) { //3
        NSLog(@"subscribeNext - %@", x);
    }];
}

#define RACObserve(TARGET, KEYPATH) \
    ({ \
        _Pragma("clang diagnostic push") \
        _Pragma("clang diagnostic ignored \"-Wreceiver-is-weak\"") \
        __weak id target_ = (TARGET); \
        [target_ rac_valuesForKeyPath:@keypath(TARGET, KEYPATH) observer:self]; \
        _Pragma("clang diagnostic pop") \
    })

- (void)viewDidLoad
{
    [super viewDidLoad];
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id < RACSubscriber > subscriber) { //1
        GJModel *model = [[GJModel alloc] init];
        [subscriber sendNext:model];
        [subscriber sendCompleted];
        return nil;
    }]; 
    self.flattenMapSignal = [signal flattenMap:^RACStream *(GJModel *model) {//2
        __weak GJModel *target_ = model;
        return [target_ rac_valuesForKeyPath:@keypath(target_, title) observer:self];
    }];
    [self.flattenMapSignal subscribeNext:^(id x) {//3
        NSLog(@"subscribeNext - %@", x);
    }];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id < RACSubscriber > subscriber) {
        GJModel *model = [[GJModel alloc] init];
        [subscriber sendNext:model];
        [subscriber sendCompleted];
        return nil;
    }];
    @weakify(self); //
    self.signal = [signal flattenMap:^RACStream *(GJModel *model) {
        @strongify(self); //
        return RACObserve(model, title);
    }];
    [self.signal subscribeNext:^(id x) {
        NSLog(@"subscribeNext - %@", x);
    }];
}

/// Creates a signal which observes `KEYPATH` on `TARGET` for changes.
///
/// In either case, the observation continues until `TARGET` _or self_ is
/// deallocated. If any intermediate object is deallocated instead, it will be
/// assumed to have been set to nil.
///
/// Make sure to `@strongify(self)` when using this macro within a block! The
/// macro will _always_ reference `self`, which can silently introduce a retain
/// cycle within a block. As a result, you should make sure that `self` is a weak
/// reference (e.g., created by `@weakify` and `@strongify`) before the
/// expression that uses `RACObserve`.
///
/// Examples
///
///    // Observes self, and doesn't stop until self is deallocated.
///    RACSignal *selfSignal = RACObserve(self, arrayController.items);
///
///    // Observes the array controller, and stops when self _or_ the array
///    // controller is deallocated.
///    RACSignal *arrayControllerSignal = RACObserve(self.arrayController, items);
///
///    // Observes obj.arrayController, and stops when self _or_ the array
///    // controller is deallocated.
///    RACSignal *signal2 = RACObserve(obj.arrayController, items);
///
///    @weakify(self);
///    RACSignal *signal3 = [anotherSignal flattenMap:^(NSArrayController *arrayController) {
///        // Avoids a retain cycle because of RACObserve implicitly referencing
///        // self.
///        @strongify(self);
///        return RACObserve(arrayController, items);
///    }];
///
/// Returns a signal which sends the current value of the key path on
/// subscription, then sends the new value every time it changes, and sends
/// completed if self or observer is deallocated.
#define RACObserve(TARGET, KEYPATH) \
    ({ \
        _Pragma("clang diagnostic push") \
        _Pragma("clang diagnostic ignored \"-Wreceiver-is-weak\"") \
        __weak id target_ = (TARGET); \
        [target_ rac_valuesForKeyPath:@keypath(TARGET, KEYPATH) observer:self]; \
        _Pragma("clang diagnostic pop") \
    })

- (void)viewDidLoad {
    [super viewDidLoad];
    RACSubject *subject = [RACSubject subject]; //1
    [subject.rac_willDeallocSignal subscribeCompleted:^{ //2
        NSLog(@"subject dealloc");
    }];
    [subject subscribeNext:^(id x) { //3
        NSLog(@"next = %@", x);
    }];
    [subject sendNext:@1]; //4
}

2016-06-13 09:15:25.426 RAC[5366:245360] next = 1
2016-06-13 09:15:25.428 RAC[5366:245360] subject dealloc

- (void)viewDidLoad {
    [super viewDidLoad];
    RACSubject *subject = [RACSubject subject]; 
    [subject.rac_willDeallocSignal subscribeCompleted:^{ 
        NSLog(@"subject dealloc");
    }];

    [[subject map:^id(NSNumber *value) { 
        return @([value integerValue] * 3);
    }] subscribeNext:^(id x) { 
        NSLog(@"next = %@", x);
    }];
    [subject sendNext:@1]; 
}

2016-06-13 09:21:42.450 RAC[5404:248584] next = 3

- (void)viewDidLoad {
    [super viewDidLoad];
    RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
        [subscriber sendNext:@1];
        return nil;
    }];
    [signal.rac_willDeallocSignal subscribeCompleted:^{
        NSLog(@"signal dealloc");
    }];
    [[signal map:^id(NSNumber *value) {
        return @([value integerValue] * 3);
    }] subscribeNext:^(id x) {
        NSLog(@"next = %@", x);
    }];
}

2016-06-12 23:32:31.669 RACDemo[5085:217082] next = 3
2016-06-12 23:32:31.674 RACDemo[5085:217082] signal dealloc

- (void)viewDidLoad {
    [super viewDidLoad];
    RACSubject *subject = [RACSubject subject]; 
    [subject.rac_willDeallocSignal subscribeCompleted:^{ 
        NSLog(@"subject dealloc");
    }];

    [[subject map:^id(NSNumber *value) { 
        return @([value integerValue] * 3);
    }] subscribeNext:^(id x) { 
        NSLog(@"next = %@", x);
    }];
    [subject sendNext:@1]; 
    [subject sendCompleted];
}

2016-06-12 23:40:19.148 RAC_bindSample[5168:221902] next = 3
2016-06-12 23:40:19.153 RAC_bindSample[5168:221902] subject dealloc

- (instancetype)map:(id (^)(id value))block {
    NSCParameterAssert(block != nil);
    Class class = self.class;

    return [[self flattenMap:^(id value) {
        return [class return:block(value)];
    }] setNameWithFormat:@"[%@] -map:", self.name];
}

 - (instancetype)flattenMap:(RACStream * (^)(id value))block {
    Class class = self.class;
    return [[self bind:^{
        return ^(id value, BOOL *stop) {
            id stream = block(value) ?: [class empty];
            NSCAssert([stream isKindOfClass:RACStream.class], @"Value returned from -flattenMap: is not a stream: %@", stream);
            return stream;
        };
    }] setNameWithFormat:@"[%@] -flattenMap:", self.name];
}

 - (RACSignal *)bind:(RACStreamBindBlock (^)(void))block {
    NSCParameterAssert(block != NULL);
    /*
     * -bind: should:
     * 
     * 1. Subscribe to the original signal of values.
     * 2. Any time the original signal sends a value, transform it using the binding block.
     * 3. If the binding block returns a signal, subscribe to it, and pass all of its values through to the subscriber as they're received.
     * 4. If the binding block asks the bind to terminate, complete the _original_ signal.
     * 5. When _all_ signals complete, send completed to the subscriber.
     * 
     * If any signal sends an error at any point, send that to the subscriber.
     */
    return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
        RACStreamBindBlock bindingBlock = block();
        NSMutableArray *signals = [NSMutableArray arrayWithObject:self];
        // 此处省略了80行代码
        // ...
    }] setNameWithFormat:@"[%@] -bind:", self.name];
}

NSMutableArray *signals = [NSMutableArray arrayWithObject:self];

RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
    // Manually check disposal to handle synchronous errors.
    if (compoundDisposable.disposed) return;
    BOOL stop = NO;
    id signal = bindingBlock(x, &stop);
    @autoreleasepool {
        if (signal != nil) addSignal(signal);
        if (signal == nil || stop) {
            [selfDisposable dispose];
            completeSignal(self, selfDisposable);
        }
    }
} error:^(NSError *error) {
    //...
} completed:^{
    //...
}];

void (^addSignal)(RACSignal *) = ^(RACSignal *signal) {
    @synchronized (signals) {
        [signals addObject:signal];
    }
    //...
};

RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
    //...
} error:^(NSError *error) {
    //...
} completed:^{
    @autoreleasepool {
        completeSignal(self, selfDisposable);
    }
}];

void (^completeSignal)(RACSignal *, RACDisposable *) = ^(RACSignal *signal, RACDisposable *finishedDisposable) {
    BOOL removeDisposable = NO;
    @synchronized (signals) {
        [signals removeObject:signal]; //1
        if (signals.count == 0) {
            [subscriber sendCompleted]; //2
            [compoundDisposable dispose]; //3
        } else {
            removeDisposable = YES;
        }
    }
    if (removeDisposable) [compoundDisposable removeDisposable:finishedDisposable]; //4
};

RACSignal *signal = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
    [subscriber sendNext:@1];
    [subscriber sendCompleted]; // 保证源信号发送完成
    return nil;
}];

RACSignal *replaySignal = [signal replay]; // 这里返回的其实是一个RACReplaySubject

[[replaySignal map:^id(NSNumber *value) {
    return @([value integerValue] * 3);
}] subscribeNext:^(id x) {
    NSLog(@"subscribeNext - %@", x);
}];