RACChannelTo

<code>
RACChannelTo(self, name) = RACChannelTo(self.model, name);
RACChannelTo(self, blurb) = RACChannelTo(self.model, blurb);
RACChannelTo(self, filmType, @(ASHRecipeFilmTypeColourNegative)) = RACChannelTo(self.model, filmType, @(ASHRecipeFilmTypeColourNegative));
</code>
这是一个双向绑定，self.name和self.model.name任何一个改变，另外一个也会改变。第三个参数是默认值，出现nil就用这个来代替。有了它，model和ViewModel就可以双向同步。

<code>
RACChannelTerminal *channelA = RACChannelTo(self, valueA);
RACChannelTerminal *channelB = RACChannelTo(self, valueB);
[[channelA map:^id(NSString value) {
if ([value isEqualToString:@"西"]) {
return @"东";
}
return value;
}] subscribe:channelB];
[[channelB map:^id(NSString value) {
if ([value isEqualToString:@"左"]) {
return @"右";
}
return value;
}] subscribe:channelA];
[[RACObserve(self, valueA) filter:^BOOL(id value) {
return value ? YES : NO;
}] subscribeNext:^(NSString x) {
NSLog(@"你向%@", x);
}];
[[RACObserve(self, valueB) filter:^BOOL(id value) {
return value ? YES : NO;
}] subscribeNext:^(NSString x) {
NSLog(@"他向%@", x);
}];
self.valueA = @"西";
self.valueB = @"左";
</code>