//YOU CAN USE THIS FUNCTION IN THE SHARED LIBRARY CODE (WHEREEVER YOU WANT TO USE IT)

           private void Button_Clicked(object sender, EventArgs e)  

           {  

               MessagingCenter.Send<object,string>(this, "ChangeOrientation", "Landscape");  

           }

​

​

          /// YOU NEED TO ADD THIS IN THE OnCreate method of the MainActivity

           protected override void OnCreate(Bundle savedInstanceState)  

           {  

               TabLayoutResource = Resource.Layout.Tabbar;  

               ToolbarResource = Resource.Layout.Toolbar;  

               base.OnCreate(savedInstanceState);  

               MessagingCenter.Subscribe<object,string>(this, "ChangeOrientation", (sender,args) =>  

               {  

                   if(args == "Landscape")  

                   {  

                       RequestedOrientation = ScreenOrientation.Landscape;  

                   }  

                   else if (args == "Portrait")  

                   {  

                       RequestedOrientation = ScreenOrientation.Portrait;  

                   }              

               });  

               Xamarin.Essentials.Platform.Init(this, savedInstanceState);  

               global::Xamarin.Forms.Forms.Init(this, savedInstanceState);  

               LoadApplication(new App());  

            }