title: UIButton RAC binding
body: <p>I started study MVVM pattern with Reactive Cocoa and now I have some unclear situation. I want to bind <code>enable</code> property of button with my model and bind <code>rac_command</code> also. Here is a my code :</p>
  
  <pre><code>RAC(self.loginButton, enabled) = RACObserve(self.viewModel, loginButtonEnabled);
  RAC(self.loginButton, rac_command) = RACObserve(self.viewModel, loginCommand);
  
  - (RACCommand *)rac_loginCommand {
      return [[RACCommand alloc] initWithSignalBlock:^RACSignal *(id input) {
          return [RACSignal empty];
      }];
  }
  </code></pre>
  
  <p>But it's doesn't work. </p>
  
  <pre><code>'Signal &lt;RACDynamicSignal: 0x7f805bf05b30&gt; name:  is already bound to key path "enabled" on object &lt;Button: 0x7f805bc3eae0;
  </code></pre>
  
  <p>Hope someone can help me. </p>