title: android facebook login do not show pop up dialog
body: <p>I integrated my app with Facebook SDK successfully. But currently when the user presses the login button my app opens Login activity as follows:</p>
  
  <p><img src="https://i.stack.imgur.com/cAT8C.png" alt="https://fbcdn-dragon-a.akamaihd.net/hphotos-ak-xpa1/t39.2178-6/851562_376550965784116_2050104420_n.png"></p>
  
  <p>What I want is to open the login dialog as in below:</p>
  
  <p><img src="https://i.stack.imgur.com/XHoUV.png" alt="enter image description here"></p>
  
  <p>How do I do this?</p>