title: Android app(host) button click event to invoke a flutter method
body: <p>I've added Flutter module to existing Android project.<br>
  as per this link.
  <a href="https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps" rel="nofollow noreferrer">https://github.com/flutter/flutter/wiki/Add-Flutter-to-existing-apps</a></p>
  
  <p>And able to display flutter widget using Flutter createFragment as below method </p>
  
  <pre><code>FragmentTransaction tx = getSupportFragmentManager().beginTransaction();
  tx.replace(R.id.someContainer, Flutter.createFragment("route1"));
  tx.commit();
  </code></pre>
  
  <p>Now, i want to invoke a method in Flutter module, when click on a button in Android app. When i search for it, I see about MethodChannel and EventChannel to pass data. I'm not sure how to use them in host Android app. or Is there any other way for it.</p>
  
  <p>Please let me know on it.</p>
  
  <p>Thank you.</p>