c# - how to call xaml file on button onclick event in windows phone 8 -

i have 1 html page contains 3 button.in 1 button after clicking should goto contact list ,pick contact , come index.html page.i tried code contact chooser sepratly , runs correctly m not getting how call same contact chooser button onclick funtion.please if knows thanks.this code below contact chooser

using system; using system.collections.generic; using system.linq; using system.net; using system.windows; using system.windows.controls; using system.windows.documents; using system.windows.input; using system.windows.media; using system.windows.media.animation; using system.windows.shapes; using microsoft.phone.controls; using microsoft.phone.tasks; using system.io; using system.windows.media.imaging; using system.windows.resources;   namespace cordovawp8_2_8_03 {     public partial class mainpage : phoneapplicationpage     {         phonenumberchoosertask phonenumberchoosertask;         // constructor         public mainpage()         {             initializecomponent();              phonenumberchoosertask = new phonenumberchoosertask();             phonenumberchoosertask.completed += new eventhandler<phonenumberresult>(phonenumberchoosertask_completed);             phonenumberchoosertask.show();          }         void phonenumberchoosertask_completed(object sender, phonenumberresult e)         {             if (e.taskresult == taskresult.ok)             {                 messagebox.show("the phone number " + e.displayname + " " + e.phonenumber);                  // phonecalltask phonecalltask = new phonecalltask();               //  phonecalltask.displayname = e.displayname;                // phonecalltask.phonenumber = e.phonenumber;               //  phonecalltask.show();             }         }        }