由于新入职的团队使用的是RAC，因此需要熟悉一下RAC的类图和大致的实现。 类图大致如下：
RACSequence
和Cocoa内置的集合对象(NSArray，NSSet)类似，内部不能包含nil，是RACStream（一个抽象类，用于表示为信号流的值）的子类，RACSequence是拉力驱动(被动)的数据流，因此默认是惰性求值，并且当调用map或falttenMap之类的方法时，block对内部的对象求值只会进行一次。
借用RAC官方Demo
NSArray *strings = @[ @"A", @"B", @"C" ];
RACSequence *sequence = [strings.rac_sequence map:^(NSString *str) {
NSLog(@"%@", str);
return [str stringByAppendingString:@"_"];
}];
// Logs "A" during this call.
NSString *concatA = sequence.head;
// Logs "B" during this call.
NSString *concatB = sequence.tail.head;
// Does not log anything.
NSString *concatB2 = sequence.tail.head;
RACSequence *derivedSequence = [sequence map:^(NSString *str) {
return [@"_" stringByAppendingString:str];
}];
// Does not log anything, and concatA2 value is A_ ,NOT _A_
NSString *concatA2 = sequence.head;
RACSignal
RACSignal是专注于解决通过订阅信号来异步进行事件传输
RAC是线程安全的，因此可以在任意线程进行signal发送，但是一个订阅者只能串行的处理一个信号，而不能并发的处理多个信号。
因此-subscribeNext:error:completed:的 block不需要进行synchronized。
bind
利用一段代码来测试bind函数的调用顺序,由于代码结构复杂，所以在bind模块对应的block都会标有数字，方便描述调用顺序。
RACSignal *sourceSig = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
//doSomething
//...
//...block1
NSLog(@"\nbegin---\n%@\n---end",@"dosomething");
[subscriber sendNext:@"hello world"];
// [subscriber sendCompleted];
return nil;
}];
RACSignal *bindSig = [sourceSig bind:^RACStreamBindBlock{
//block2
return ^(id value, BOOL *stop) {
//block3
//这里对value进行处理
return [RACSignal return:value];
};
}];
[bindSig subscribeNext:^(id x) {
//block4
NSLog(@"\nbegin---\n%@\n---end",x);
}];
1.createSignal：的作用是将传的:^RACDisposable *(id<RACSubscriber> subscriber)这个block存到sourceSig的didSubscribe字段中（block1）
2.bind:通过调用createSignal：返回一个新的信号bindSig，bind: 的参数是一个没有入参，返回值为RACStreamBindBlock的block(block2)。
RACStreamBindBlock入参和出参如下：
typedef RACSignal * _Nullable (^RACSignalBindBlock)(ValueType _Nullable value, BOOL *stop);
通过改变传入进来的Value（也就是改变block3的内部实现 ），从而实现了flattenMap:,skip:,takeUntilBlock:,distinctUntilChanged：等高级操作。
- (RACSignal *)bind:(RACSignalBindBlock (^)(void))block {
//返回bindSig，并将block保存至didSubscribe
return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
//省略didSubscribe内部代码
}] setNameWithFormat:@"[%@] -bind:", self.name];
}
3.当bindSig 调用subscribeNext：，生成一个RACSubscriber，并将nextBlock保存在_next中
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
NSCParameterAssert(nextBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
return [self subscribe:o];
}
然后bindSig调用subscribe：，入参就是这个subscribe
4.在subcribe：中，调用bindSig保存的didSubscribe ,执行一长串代码（block5）
return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
//block5
RACStreamBindBlock bindingBlock = block();
//这里的self是sourceSig
NSMutableArray *signals = [NSMutableArray arrayWithObject:self];
RACCompoundDisposable *compoundDisposable = [RACCompoundDisposable compoundDisposable];
void (^completeSignal)(RACSignal *, RACDisposable *) = ^(RACSignal *signal, RACDisposable *finishedDisposable) {
//block6
BOOL removeDisposable = NO;
@synchronized (signals) {
[signals removeObject:signal];
if (signals.count == 0) {
[subscriber sendCompleted];
[compoundDisposable dispose];
} else {
removeDisposable = YES;
}
}
if (removeDisposable) [compoundDisposable removeDisposable:finishedDisposable];
};
void (^addSignal)(RACSignal *) = ^(RACSignal *signal) {
//block7
@synchronized (signals) {
[signals addObject:signal];
}
RACSerialDisposable *selfDisposable = [[RACSerialDisposable alloc] init];
[compoundDisposable addDisposable:selfDisposable];
//4.订阅newSig，然后将newSig的值传给bindSig的订阅者，执行block8
RACDisposable *disposable = [signal subscribeNext:^(id x) {
//block8
//这里是subscriber对应的是bindSig
[subscriber sendNext:x];
//5.然后执行block4
} error:^(NSError *error) {
[compoundDisposable dispose];
[subscriber sendError:error];
} completed:^{
@autoreleasepool {
completeSignal(signal, selfDisposable);
}
}];
selfDisposable.disposable = disposable;
};
@autoreleasepool {
RACSerialDisposable *selfDisposable = [[RACSerialDisposable alloc] init];
[compoundDisposable addDisposable:selfDisposable];
//1.先执行block1，然后执行block9
RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
// Manually check disposal to handle synchronous errors.
//block9
if (compoundDisposable.disposed) return;
BOOL stop = NO;
//对sourceSig传的值进行处理，再包装在新值（可为nil)简称newSig
//2.再执行block3
id signal = bindingBlock(x, &stop);
@autoreleasepool {
//3.假如block3返回的sig不为nil执行block7
if (signal != nil) addSignal(signal);
//假如block3返回的sig为nil或者stop指针为YES，执行block6
if (signal == nil || stop) {
[selfDisposable dispose];
completeSignal(self, selfDisposable);
}
}
} error:^(NSError *error) {
[compoundDisposable dispose];
[subscriber sendError:error];
} completed:^{
@autoreleasepool {
completeSignal(self, selfDisposable);
}
}];
selfDisposable.disposable = bindingDisposable;
}
return compoundDisposable;
}] setNameWithFormat:@"[%@] -bind:", self.name];
总结一下bind的作用：生成一个新的信号bindSig，订阅源信号sourceSig，当sourceSig发送一个值时，bindSig通过订阅收到这个值后,根据上层传的RACStreamBindBlock转换value,发送给bindSig的subscriber。
ATTENTION
由于RACSignal是冷信号，所以每次有新的订阅都会触发副作用(对应的block)，这意味着 singal对应的block会执行多次。
__block int missilesToLaunch = 0;
// Signal that will have the side effect of changing `missilesToLaunch` on
// subscription.
RACSignal *processedSignal = [[RACSignal return:@"missiles"]
map:^(id x) {
missilesToLaunch++;
return [NSString stringWithFormat:@"will launch %d %@", missilesToLaunch, x];
}];
// This will print "First will launch 1 missiles"
[processedSignal subscribeNext:^(id x) {
NSLog(@"First %@", x);
}];
// This will print "Second will launch 2 missiles"
[processedSignal subscribeNext:^(id x) {
NSLog(@"Second %@", x);
}];
假如想冷信号执行一次，就得转换成热信号。比如网络请求肯定只需要一次就好，所以在业务场景中通过multicast使用，可以避免冷信号的的多次调用
// This signal starts a new request on each subscription.
RACSignal *networkRequest = [RACSignal createSignal:^(id<RACSubscriber> subscriber) {
AFHTTPRequestOperation *operation = [client
HTTPRequestOperationWithRequest:request
success:^(AFHTTPRequestOperation *operation, id response) {
[subscriber sendNext:response];
[subscriber sendCompleted];
}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
[subscriber sendError:error];
}];
[client enqueueHTTPRequestOperation:operation];
return [RACDisposable disposableWithBlock:^{
[operation cancel];
}];
}];
// Starts a single request, no matter how many subscriptions `connection.signal`
// gets. This is equivalent to the -replay operator, or similar to
// +startEagerlyWithScheduler:block:.
// single中除了Subject之外的都是冷信号，Subject是热信号。
RACMulticastConnection *connection = [networkRequest multicast:[RACReplaySubject subject]];
[connection connect];
[connection.signal subscribeNext:^(id response) {
NSLog(@"subscriber one: %@", response);
}];
[connection.signal subscribeNext:^(id response) {
NSLog(@"subscriber two: %@", response);
}];
当我们需要在nextBlock之前需要加一些副作用代码，就可以调用-doNext，这时候会先调用这里的block，再调用subscriber的sendNext。
UI事件
RAC(self.label,text,@"nil的值") = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
__block int i = 0;
[[self.button rac_signalForControlEvents:UIControlEventTouchDown] subscribeNext:^(id x) {
i ++;
if (i > 3) {
[subscriber sendNext:nil];
}
else {
[subscriber sendNext:@"123"];
}
}];
return nil;
}];
通知
当我们用RAC来改写NSNotification的时候用rac_addObserverForName:
比如我们需要监听网络状态时
//当网络发生变化后，RAC这个宏会进行keypath绑定，会将self.NetWorkStatus 赋予新值，这时其他利用RACObserve会收到这个变化并作出对应改
RAC(self, NetWorkStatus) = [[[[NSNotificationCenter defaultCenter]
rac_addObserverForName:kRealReachabilityChangedNotification object:nil]
map:^(NSNotification *notification) {
return @([notification.object currentReachabilityStatus]);
}]
distinctUntilChanged];
//RACObserve接受新值并订阅信号
[RACObserve(self , NetWorkStatus) subscribeNext:^(NSNumber *networkStatus) {
@strongify(self);
if (networkStatus.integerValue == RealStatusNotReachable || networkStatus.integerValue == RealStatusUnknown) {
[self.viewModel showErrorView];
}else{
[self.viewModel request];
}
}];
协议
@weakify(self);
[[self
rac_signalForSelector:@selector(webViewDidStartLoad:)
fromProtocol:@protocol(WebViewDelegate)]
subscribeNext:^(RACTuple *tuple) {
@strongify(self)
if (tuple.first == self.webView){
dispatch_main_async_safe(^{
[self showStatusWithMessage:@"Loading..."];
});
}
}];
网络事件（耗时事件）
__block int callCount = 0;
这里因为订阅了两次，所以会调用两次block，因此假如是io类操作，最好将networkSig包装成RACSubject然后通过multicast广播
self.networkSig = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
__block int i = 0;
callCount ++;
//打印两次
NSLog(@"\nbegin---\n callCount ==%d\n---end",callCount );
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
i++;
[subscriber sendNext:@(i)];
});
return nil;
}];
[self.networkSig subscribeNext:^(id x) {
NSLog(@"\nbegin---\nfirst i ==== %@\n---end", x);
}];
[self.networkSig subscribeNext:^(id x) {
NSLog(@"\nbegin---\nsecond i ==== %@\n---end", x);
}];
改进后:
__block int callCount = 0;
self.networkSig = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
__block int i = 0;
callCount ++;
//只会打印一次
NSLog(@"\nbegin---\n callCount ==%d\n---end",callCount );
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.f * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
i++;
[subscriber sendNext:@(i)];
});
return nil;
}];
RACSubject *subject = [RACSubject subject];
RACMulticastConnection *multicastConnection = [self.networkSig multicast:subject];
[multicastConnection connect];
[multicastConnection.signal subscribeNext:^(id x) {
NSLog(@"\nbegin---\nfirst i ==== %@\n---end", x);
}];
[multicastConnection.signal subscribeNext:^(id x) {
NSLog(@"\nbegin---\nsecond i ==== %@\n---end", x);
}];
KVO
//实现self.navigationItem.title 和 self.viewModel.title的单向绑定
RAC(self.navigationItem,title) = RACObserve(self.viewModel, title);
RACCommand
创建RACCommand的时候需要返回一个signal，当调用execute:,signal必须调用sendCompleted或sendError:,command才能进行下次execute:
初学者可能会想当然如下写代码
//1.先绑定self.button的keypath:enable
RAC(self.button,enabled) = [RACSignal combineLatest:@[self.userNameField.rac_textSignal,self.passwordField.rac_textSignal]
reduce:^id(NSString *userName,NSString *password){
return @(userName.length >= 8 && password.length >= 6);
}];
//2.然后设置button的点击事件
self.button.rac_command = [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
return [self login];
}];
这时候运行程序的时候报错
RAC()这个宏和button.rac_command都会调用setKeyPath:onObject:nilValue:这个方法。
首次调用时，会通过objc_setAssociatedObject将keypath保存起来，当重复调用相同的keypath的时候会触发NSCAssert
正确的做法是
RACSignal *buttonEnabled = [RACSignal combineLatest:@[self.userNameField.rac_textSignal,self.passwordField.rac_textSignal]
reduce:^id(NSString *userName,NSString *password){
return @(userName.length >= 8 && password.length >= 6);
}];
self.button.rac_command = [[RACCommand alloc] initWithEnabled:buttonEnabled signalBlock:^RACSignal *(id input) {
return [self login];
}];
