由於新入職的團隊使用的是RAC，因此需要熟悉一下RAC的類圖和大致的實現。 類圖大致如下：
RACSequence
和Cocoa內建的集合物件(NSArray，NSSet)類似，內部不能包含nil，是RACStream（一個抽象類，用於表示為訊號流的值）的子類，RACSequence是拉力驅動(被動)的資料流，因此預設是惰性求值，並且當呼叫map或falttenMap之類的方法時，block對內部的物件求值只會進行一次。
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;
複製程式碼RACSignal
RACSignal是專注於解決通過訂閱訊號來非同步進行事件傳輸
RAC是執行緒安全的，因此可以在任意執行緒進行signal傳送，但是一個訂閱者只能序列的處理一個訊號，而不能併發的處理多個訊號。
因此-subscribeNext:error:completed:的 block不需要進行synchronized。
bind
利用一段程式碼來測試bind函式的呼叫順序,由於程式碼結構複雜，所以在bind模組對應的block都會標有數字，方便描述呼叫順序。
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
//這裡對value進行處理
return [RACSignal return:value];
};
}];
[bindSig subscribeNext:^(id x) {
//block4
NSLog(@"\nbegin---\n%@\n---end",x);
}];
複製程式碼1.createSignal：的作用是將傳的:^RACDisposable *(id<RACSubscriber> subscriber)這個block存到sourceSig的didSubscribe欄位中（block1）
2.bind:通過呼叫createSignal：返回一個新的訊號bindSig，bind: 的引數是一個沒有入參，返回值為RACStreamBindBlock的block(block2)。
RACStreamBindBlock入參和出參如下：
typedef RACSignal * _Nullable (^RACSignalBindBlock)(ValueType _Nullable value, BOOL *stop);
複製程式碼通過改變傳入進來的Value（也就是改變block3的內部實現 ），從而實現了flattenMap:,skip:,takeUntilBlock:,distinctUntilChanged：等高階操作。
- (RACSignal *)bind:(RACSignalBindBlock (^)(void))block {
//返回bindSig，並將block儲存至didSubscribe
return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
//省略didSubscribe內部程式碼
}] setNameWithFormat:@"[%@] -bind:", self.name];
}
複製程式碼3.當bindSig 呼叫subscribeNext：，生成一個RACSubscriber，並將nextBlock儲存在_next中
- (RACDisposable *)subscribeNext:(void (^)(id x))nextBlock {
NSCParameterAssert(nextBlock != NULL);
RACSubscriber *o = [RACSubscriber subscriberWithNext:nextBlock error:NULL completed:NULL];
return [self subscribe:o];
}
複製程式碼然後bindSig呼叫subscribe：，入參就是這個subscribe
4.在subcribe：中，呼叫bindSig儲存的didSubscribe ,執行一長串程式碼（block5）
return [[RACSignal createSignal:^(id<RACSubscriber> subscriber) {
//block5
RACStreamBindBlock bindingBlock = block();
//這裡的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.訂閱newSig，然後將newSig的值傳給bindSig的訂閱者，執行block8
RACDisposable *disposable = [signal subscribeNext:^(id x) {
//block8
//這裡是subscriber對應的是bindSig
[subscriber sendNext:x];
//5.然後執行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.先執行block1，然後執行block9
RACDisposable *bindingDisposable = [self subscribeNext:^(id x) {
// Manually check disposal to handle synchronous errors.
//block9
if (compoundDisposable.disposed) return;
BOOL stop = NO;
//對sourceSig傳的值進行處理，再包裝在新值（可為nil)簡稱newSig
//2.再執行block3
id signal = bindingBlock(x, &stop);
@autoreleasepool {
//3.假如block3返回的sig不為nil執行block7
if (signal != nil) addSignal(signal);
//假如block3返回的sig為nil或者stop指標為YES，執行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];
複製程式碼總結一下bind的作用：生成一個新的訊號bindSig，訂閱源訊號sourceSig，當sourceSig傳送一個值時，bindSig通過訂閱收到這個值後,根據上層傳的RACStreamBindBlock轉換value,傳送給bindSig的subscriber。
ATTENTION
由於RACSignal是冷訊號，所以每次有新的訂閱都會觸發副作用(對應的block)，這意味著 singal對應的block會執行多次。
__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);
}];
複製程式碼假如想冷訊號執行一次，就得轉換成熱訊號。比如網路請求肯定只需要一次就好，所以在業務場景中通過multicast使用，可以避免冷訊號的的多次呼叫
// 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之外的都是冷訊號，Subject是熱訊號。
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);
}];
複製程式碼當我們需要在nextBlock之前需要加一些副作用程式碼，就可以呼叫-doNext，這時候會先呼叫這裡的block，再呼叫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;
}];
複製程式碼通知
當我們用RAC來改寫NSNotification的時候用rac_addObserverForName:
比如我們需要監聽網路狀態時
//當網路發生變化後，RAC這個巨集會進行keypath繫結，會將self.NetWorkStatus 賦予新值，這時其他利用RACObserve會收到這個變化並作出對應改
RAC(self, NetWorkStatus) = [[[[NSNotificationCenter defaultCenter]
rac_addObserverForName:kRealReachabilityChangedNotification object:nil]
map:^(NSNotification *notification) {
return @([notification.object currentReachabilityStatus]);
}]
distinctUntilChanged];
//RACObserve接受新值並訂閱訊號
[RACObserve(self , NetWorkStatus) subscribeNext:^(NSNumber *networkStatus) {
@strongify(self);
if (networkStatus.integerValue == RealStatusNotReachable || networkStatus.integerValue == RealStatusUnknown) {
[self.viewModel showErrorView];
}else{
[self.viewModel request];
}
}];
複製程式碼協議
@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..."];
});
}
}];
複製程式碼網路事件（耗時事件）
__block int callCount = 0;
這裡因為訂閱了兩次，所以會呼叫兩次block，因此假如是io類操作，最好將networkSig包裝成RACSubject然後通過multicast廣播
self.networkSig = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
__block int i = 0;
callCount ++;
//列印兩次
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);
}];
複製程式碼改進後:
__block int callCount = 0;
self.networkSig = [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {
__block int i = 0;
callCount ++;
//只會列印一次
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);
}];
複製程式碼KVO
//實現self.navigationItem.title 和 self.viewModel.title的單向繫結
RAC(self.navigationItem,title) = RACObserve(self.viewModel, title);
複製程式碼RACCommand
建立RACCommand的時候需要返回一個signal，當呼叫execute:,signal必須呼叫sendCompleted或sendError:,command才能進行下次execute:
初學者可能會想當然如下寫程式碼
//1.先繫結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.然後設定button的點選事件
self.button.rac_command = [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
return [self login];
}];
複製程式碼這時候執行程式的時候報錯
RAC()這個巨集和button.rac_command都會呼叫setKeyPath:onObject:nilValue:這個方法。
首次呼叫時，會通過objc_setAssociatedObject將keypath儲存起來，當重複呼叫相同的keypath的時候會觸發NSCAssert
正確的做法是
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];
}];
複製程式碼