Dispatcher.BeginInvoke not working in UWP Visual Studio 2015

Question

Can anyone please tell me that why BeginInvoke is not working in Universal Windows Platform applications ..Here's the code  

 

Dispatcher.BeginInvoke();

In this code I want to access the BeginInvoke using Dispatcher class but visual studio 2015 gives me a error that is you're missing an assembly reference .

Anyone tell me what's problem with my code .