Check out example codes for "xamarin native display alert android". It will help you in understanding the concepts better.

Code Example 1

TaskCompletionSource<bool> taskCompletionSource;
taskCompletionSource = new TaskCompletionSource<bool>();

Android.App.AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.Instance);
AlertDialog alert = dialog.Create();
alert.SetTitle("Title");
alert.SetMessage("Complex Alert");
alert.SetButton("OK", (c, ev) =>
                {
                  // Ok button click task 
                  Console.WriteLine("Okay was clicked");
                  taskCompletionSource.SetResult(true);
                });
alert.SetButton2("CANCEL", (c, ev) =>
                 {
                   Console.WriteLine("Cancel was clicked");
                   taskCompletionSource.SetResult(false);
                 });
alert.Show();

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