title: Fill all the screen with StackLayout
body: <p>I have a StackLayout coded like this:</p>
  
  <pre class="lang-cs prettyprint-override"><code>StackLayout mainStackLayOut = new StackLayout{
      BackgroundColor = Color.Blue,
      //VerticalOptions = LayoutOptions.FillAndExpand,
      //WidthRequest = width,
      HorizontalOptions = LayoutOptions.FillAndExpand,
      Orientation = StackOrientation.Vertical
  };
  </code></pre>
  
  <p>But I want the StackLayout to fill all the screen width and height, also I have tree buttons added like this:</p>
  
  <pre class="lang-cs prettyprint-override"><code>StackLayout buttonsStackLayOut = new StackLayout
  {
      BackgroundColor = Color.White,
      //VerticalOptions = LayoutOptions.Fill,
      HorizontalOptions = LayoutOptions.Fill,
      Orientation = StackOrientation.Horizontal,
      Spacing = 0
  };
  mainStackLayOut.Children.Add(buttonsStackLayOut);
  
  
  Image doctorImage = new Image
  {
      WidthRequest = width / 3,
      HeightRequest = 50,
      BackgroundColor = Color.Gray,
      Source = ImageSource.FromFile ("about.png")
  };
  buttonsStackLayOut.Children.Add(doctorImage);
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/TDL7U.png" alt="enter image description here"></p>
  
  <p>How can I fill all the screensize?</p>