Passing elements between pages in C# Xaml -

first pass content of button mainpage menu2:

private void button2click(object sender, routedeventargs args)     {         // create passdata object         passdata passdata = new passdata();          // set initializedata property button's content         passdata.data = firstelement.content;          // pass object navigate         this.frame.navigate(typeof(menu2), passdata);      } 

then retrieve data within menu2 page:

// pulling data first page selection     protected override void onnavigatedto(navigationeventargs args)     {         // object passed second argument navigate         passdata passdata = args.parameter passdata;          // use initilize button         firstelement.content = passdata.data;          base.onnavigatedto(args);     } 

at point button's content passed without problems.

then want pass data mainpage again:

menu2 code:

private void button1click(object sender, routedeventargs args)     {         // create passdata object         passdata passdata = new passdata();          // set initializedata property button's content         passdata.data = firstelement.content;          // pass object navigate         this.frame.navigate(typeof(mainpage), passdata);      } 

and try retrieve data in mainpage:

// pulling data menu2's button     protected override void onnavigatedto(navigationeventargs args)     {         // object passed second argument navigate         passdata passdata = args.parameter passdata;          // use initilize button         firstelement.content = passdata.data;          base.onnavigatedto(args);     } 

at point error on mainpage's line:

firstelement.content = passdata.data; 

the error says:

null reference exception, object reference not set instance of object 

what doing wrong?

so 1 first page load ?

when load 1 in first time, passdata null.

i guess working on uwp, should create , pass passdata() argument in file app.cs when navigate mainpage.