title: How to observe the value in array with RxSwift
body: <p>There is class have a Bool property  </p>
  
  <pre><code>class Coupon: NSObject {
      var invalid: Bool = false
  }
  </code></pre>
  
  <p>I create a array [Coupon],I need to modify the coupon.invalid to true one by one.when all of these coupon.invalid == true ,then I can process next task,How can I implement this logic with RxSwift ?Please help me ~~</p>