通过Reactivecocoa绑定UISwitch到NSUserDefault

RACChannelTerminal *switchTerminal = self.someSwitch.rac_newOnChannel;
RACChannelTerminal *defaultsTerminal = [[NSUserDefaults standardUserDefaults] rac_channelTerminalForKey:@"someBoolKey"];

[switchTerminal subscribe:defaultsTerminal];
[defaultsTerminal subscribe:switchTerminal];

参考:

http://stackoverflow.com/questions/23107136/bind-uiswitchs-state-to-nsuserdefaults-with-reactivecocoa