title: android check if a contact installed an app android (like whatsapp)
body: <p>I want to let my app scan the users contactlist , and display the name of the contacts who also installed the app. </p>
  
  <p>I have no idea where to begin with this . so if someone could help me getting started , that would be apreciated. </p>
  
  <p>grtz</p>