Xamarin.Forms.Device.BeginInvokeOnMainThread(() => {
                        MessagingCenter.Send(App.Current, "log", e1.Message +"\r\n"+ e1.Source); // 这里更新UI。
                    });

1 FusionField.currentActivity.runOnUiThread(new Runnable()    
2         {    
3             public void run()    
4             {    
5                 Toast.makeText(getApplicationContext(), , "Update My UI",    
6                         Toast.LENGTH_LONG).show();    
7             }    
8     
9         });