title: StateManagement with provider package
body: <p>recently Im working with provider and im happy so far ,,, the problem is i want to show a loading screen [with the help if flutter_spinKit package ] while the user has pressed the sign in buton is waiting to get into the home page ....normally with set state and staefull widget we follow these lines below:</p>
  <p>1.create a boolean variable and set to false</p>
  <ol>
  <li><p>ternoray operator in the return value of the build method :</p>
  <pre><code>return isLoading ? LoadingPage() : Scaffold(
  </code></pre>
  </li>
  <li><p>set to true when th textfields are valid</p>
  </li>
  <li><p>set to false again when we are sure there arent any error with the textfiled or null user...
  I dont want to use stateful widget or setstate anymore please help me how to provide this logic with provider5
  if there is any advice on statemanagement in flutter Im all up ears.
  I appreciate your help inadvance...</p>
  </li>
  </ol>