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[操作系统]ReactiveCocoa基础知识内容2


引用网络上一些实例的代码,针对ReactiveCocoa的运用可以更加有帮助;

 

1:跟AF结合时的写法,返回RACSignal

- (RACSignal *)fetchQuestionWithTag:(NSString *)tag {    NSString *relativeURL = [NSString stringWithFormat:@"http://api.stackexchange.com/2.1/questions/?site=stackoverflow&order=desc&sort=hot&tagged=%@", tag];  RACSignal *signal =    [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) {          AFHTTPRequestOperation *operation = [       [AFHTTPRequestOperationManager manager]       GET:relativeURL       parameters:nil       success:^(AFHTTPRequestOperation *operation, NSDictionary *responseObject) {                  [subscriber sendNext:responseObject[@"items"]];         [subscriber sendCompleted];       }       failure:^(AFHTTPRequestOperation *operation, NSError *error){         [subscriber sendError:error];       }];            return [RACDisposable disposableWithBlock:^{        [operation cancel];      }];    }];  return signal;  }

 2:RACCommand的运用,作为事件响应

定义一个ViewModel@interface SubscribeViewModel : NSObject@property(nonatomic, strong) RACCommand *subscribeCommand;// write to this property@property(nonatomic, strong) NSString *email;// read from this property@property(nonatomic, strong) NSString *statusMessage;@end

@property(nonatomic, strong) RACSignal *emailValidSignal;实现代码:- (RACCommand *)subscribeCommand {  if (!_subscribeCommand) {    @weakify(self);    _subscribeCommand = [[RACCommand alloc] initWithEnabled:self.emailValidSignal signalBlock:^RACSignal *(id input) {      @strongify(self);      return [SubscribeViewModel postEmail:self.email];    }];  }  return _subscribeCommand;}+ (RACSignal *)postEmail:(NSString *)email {  AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];  manager.requestSerializer = [AFJSONRequestSerializer new];  NSDictionary *body = @{@"email": email ?: @""};  return [[[manager rac_POST:kSubscribeURL parameters:body] logError] replayLazily];}- (RACSignal *)emailValidSignal {  if (!_emailValidSignal) {    _emailValidSignal = [RACObserve(self, email) map:^id(NSString *email) {      return @([email isValidEmail]);    }];  }  return _emailValidSignal;}

调用绑定:- (void)bindWithViewModel {  RAC(self.viewModel, email) = self.emailTextField.rac_textSignal;  self.subscribeButton.rac_command = self.viewModel.subscribeCommand;  RAC(self.statusLabel, text) = RACObserve(self.viewModel, statusMessage);}- (UITextField *)emailTextField {  if (!_emailTextField) {    _emailTextField = [UITextField new];    _emailTextField.borderStyle = UITextBorderStyleRoundedRect;    _emailTextField.font = [UIFont boldSystemFontOfSize:16];    _emailTextField.placeholder = NSLocalizedString(@"Email address", nil);    _emailTextField.keyboardType = UIKeyboardTypeEmailAddress;    _emailTextField.autocapitalizationType = UITextAutocapitalizationTypeNone;  }  return _emailTextField;}- (UIButton *)subscribeButton {  if (!_subscribeButton) {    _subscribeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];    [_subscribeButton setTitle:NSLocalizedString(@"Subscribe", nil) forState:UIControlStateNormal];  }  return _subscribeButton;}- (UILabel *)statusLabel {  if (!_statusLabel) {    _statusLabel = [UILabel new];  }  return _statusLabel;}

说明:RACCommand类用于表示事件的执行,一般来说是在UI上的某些动作来触发这些事件,比如点击一个按钮。RACCommand的实例能够决定是否可以被执行,这个特性能反应在UI上,而且它能确保在其不可用时不会被执行。通常,当一个命令可以执行时,会将它的属性allowsConcurrentExecution设置为它的默认值:NO,从而确保在这个命令已经正在执行的时候,不会同时再执行新的操作。命令执行的返回值是一个RACSignal,因此我们能对该返回值进行next:,completed或error:, 

3:关于RACObserve的用法

监听对象的成员变量变化,当成员变量值被改变时,触发做一些事情。 这种情况其实就是IOS KVO机制使用的场景,使用KVO实现,通常有三个步骤:1,给对象的成员变量添加监听;2,实现监听回调;3,取消监听;而通过RAC可以直接实现,RAC的回调是通过block实现的,类似于过程式编程,上下文也更容易理解一些。

a: 场景:当前类有一个成员变量 NSString *input,当它的值被改变时,发送一个请求。

[RACObserve(self, input)   subscribeNext:^(NSString* x){     request(x);//发送一个请求   }]; 

说明:每次input值被修改时,就会调用此block,并且把修改后的值做为参数传进来。

b:场景:在上面场景中,当用户输入的值以2开头时,才发请求.

[[RACObserve(self, input)    filter:^(NSString* value){      if ([value hasPrefix:@"2"]) {        return YES;      } else {        return NO;      }    }]    subscribeNext:^(NSString* x){     request(x);//发送一个请求   }]; 

c:上面场景是监听自己的成员变量,如果想监听UITextField输入值变化,框架也做了封装可以代替系统回调

[[self.priceInput.rac_textSignal    filter:^(NSString *str) {      if (str.integerValue > 20) {        return YES;      } else {        return NO;      }    }]    subscribeNext:^(NSString *str) {   request(x);//发送一个请求 }];

d:场景:button监听 两个输入框有值和一个成员变量值,当输入框有输入且成员变量为真时,button为可点击状态

RAC(self.payButton,enabled) = [RACSignal                   combineLatest:@[self.priceInput.rac_textSignal,                         self.nameInput.rac_textSignal,                         RACObserve(self, isConnected)                         ]                   reduce:^(NSString *price, NSString *name, NSNumber *connect){                   return @(price.length > 0 && name.length > 0 && [connect boolValue]);                   }]; 

说明:同时监听多个变量变化,当这些变量满足一定条件时,使button为可点击状态

e:场景:满足上面条件时,直接发送请求

[[RACSignal                   combineLatest:@[self.priceInput.rac_textSignal,                         self.nameInput.rac_textSignal,                         RACObserve(self, isConnected)                         ]                   reduce:^(NSString *price, NSString *name, NSNumber *connect){                   return @(price.length > 0 && name.length > 0 && ![connect boolValue]);                   }]                subscribeNext:^(NSNumber *res){                  if ([res boolValue]) {                    NSLog(@"XXXXX send request");                  }                }]; 

f:distinctUntilChanged直到收到不同值才响应,可以过滤掉那些不必要的网络请求等

  @weakify(self);    //Start Binding our properties  RAC(self.nameField,text) = [RACObserve(self.viewModel, playerName) distinctUntilChanged];    [[self.nameField.rac_textSignal distinctUntilChanged] subscribeNext:^(NSString *x) {    //this creates a reference to self that when used with @weakify(self);    //makes sure self isn't retained    @strongify(self);    self.viewModel.playerName = x;  }];

 4:RACScheduler为RAC调度类(主线程,子线程等)

显示网络下载的图片

 RAC(self.imageView, image) = [[RACSignal startEagerlyWithScheduler:[RACScheduler schedulerWithPriority:RACSchedulerPriorityBackground] block:^(id <RACSubscriber> subscriber) { NSError *error; NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://ww3.sinaimg.cn/bmiddle/7128be06jw1ei4hfthoj3j20hs0bomyd.jpg"]options:NSDataReadingMappedAlwayserror:&error]; if(error) { [subscriber sendError:error];} else { [subscriber sendNext:[UIImage imageWithData:data]]; [subscriber sendCompleted];} }] deliverOn:[RACScheduler mainThreadScheduler]];

说明:这段代码会在后台线程立即发起一个请求,然后传递到主线程上更新UI,主线程上执行[RACScheduler mainThreadScheduler],信号传递:- (RACSignal *)deliverOn:(RACScheduler *)scheduler