ReactiveCocoa基礎知識內容2

標籤：

引用網路上一些執行個體的代碼，針對ReactiveCocoa的運用可以更加有協助；

 

1：跟AF結合時的寫法，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的運用，作為事件響應

定義一個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;實現代碼：- (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;}

調用綁定：- (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;}

說明：RACCommand類用於表示事件的執行，一般來說是在UI上的某些動作來觸發這些事件，比如點擊一個按鈕。RACCommand的執行個體能夠決定是否可以被執行，這個特效能反應在UI上，而且它能確保在其不可用時不會被執行。通常，當一個命令可以執行時，會將它的屬性allowsConcurrentExecution設定為它的預設值：NO，從而確保在這個命令已經正在執行的時候，不會同時再執行新的操作。命令執行的傳回值是一個RACSignal，因此我們能對該傳回值進行next:，completed或error:， 

3：關於RACObserve的用法

監聽對象的成員變數變化，當成員變數值被改變時，觸發做一些事情。 這種情況其實就是IOS KVO機制使用的情境，使用KVO實現，通常有三個步驟：1，給對象的成員變數添加監聽；2，實現監聽回調；3，取消監聽；而通過RAC可以直接實現，RAC的回調是通過block實現的，類似於過程式編程，上下文也更容易理解一些。

a: 情境：當前類有一個成員變數 NSString *input，當它的值被改變時，發送一個請求。

[RACObserve(self, input)      subscribeNext:^(NSString* x){          request(x);//發送一個請求     }]; 

說明：每次input值被修改時，就會調用此block，並且把修改後的值做為參數傳進來。

b:情境：在上面情境中，當使用者輸入的值以2開頭時，才發請求.

[[RACObserve(self, input)       filter:^(NSString* value){           if ([value hasPrefix:@"2"]) {               return YES;           } else {               return NO;           }       }]       subscribeNext:^(NSString* x){          request(x);//發送一個請求      }]; 

c:上面情境是監聽自己的成員變數，如果想監聽UITextField輸入值變化，架構也做了封裝可以代替系統回調

[[self.priceInput.rac_textSignal       filter:^(NSString *str) {           if (str.integerValue > 20) {               return YES;           } else {               return NO;           }       }]       subscribeNext:^(NSString *str) {      request(x);//發送一個請求 }];

d:情境：button監聽 兩個輸入框有值和一個成員變數值，當輸入框有輸入且成員變數為真時，button為可點擊狀態

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]);                                     }];  

說明：同時監聽多個變數變化，當這些變數滿足一定條件時，使button為可點擊狀態

e:情境：滿足上麵條件時，直接發送請求

[[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直到收到不同值才響應，可以過濾掉那些不必要的網路請求等

    @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為RAC調度類（主線程，子線程等）

顯示網路下載的圖片

 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]];

說明：這段代碼會在後台線程立即發起一個請求，然後傳遞到主線程上更新UI，主線程上執行[RACScheduler mainThreadScheduler]，訊號傳遞:- (RACSignal *)deliverOn:(RACScheduler *)scheduler

ReactiveCocoa基礎知識內容2