//创建textField获得焦点信号,当信号发生时返回@YES RACSignal *didBeginEditingSignal = [[self rac_signalForSelector:@selector(textFieldDidBeginEditing:) fromProtocol:@protocol(UITextFieldDelegate)] mapReplace:@YES]; //创建textField失去焦点信号,当信号发生时返回@NO RACSignal *didEndEditingSignal = [[self rac_signalForSelector:@selector(textFieldDidEndEditing:) fromProtocol:@protocol(UITextFieldDelegate)] mapReplace:@NO]; //合并两种信号到一个信号 RACSignal *userTextSignal = [RACSignal merge:@[didBeginEditingSignal,didEndEditingSignal]]; //doNext是信号发生时注入的边界触发.hiden为label的属性 RAC(placehold,hidden) = [userTextSignal doNext:^(id x) { NSLog(@"toggle placehold. %@",x); }];