1.RACSignal *validUsernameSignal =  [self.usernameTextField.rac_textSignal  map:^id(NSString *text) {  return @([self isValidUsername:text]);  }]; 

   RACSignal *validPasswordSignal =  [self.passwordTextField.rac_textSignal    map:^id(NSString *text) {    return @([self isValidPassword:text]);  }];  

  创建有效状态信号,map起到的作用就是做判断,如果是有效的输入则返回值,否则就不返回

  2.RAC(self.passwordTextField, backgroundColor) =

[validPasswordSignal map:^id(NSNumber *passwordValid){

return[passwordValid boolValue] ? [UIColor clearColor]:[UIColor yellowColor];

}];

RAC(self.usernameTextField, backgroundColor) =

[validUsernameSignal map:^id(NSNumber *passwordValid){

return[passwordValid boolValue] ? [UIColor clearColor]:[UIColor yellowColor];

}];

进一步改善代码,map做判断,为真返回clearcolor,假则返回yellowcolor[objc] 

  3.[[validPasswordSignal map:^id(NSNumber *passwordValid){

return[passwordValid boolValue] ? [UIColor clearColor]:[UIColor yellowColor];

}]

subscribeNext:^(UIColor *color){

self.passwordTextField.backgroundColor = color;

}];

这是完整的代码,map接收输入的text,做判断,真就返回clearcolor,假则返回yellowcolor,subscribeNext则将接收到的color作为textfield的背景颜色