Xamarin Android将MainActivity传递给AlertDialog

Question

I am trying to implement the AlertDialog by separating its code in another class and calling that class as required in the code.

Here is how i have my AlertDialog

 using Android.App;
 using Android.Content;
 using Android.OS;
 using Android.Runtime;
 using Android.Views;
 using Android.Widget;


namespace NAndroid
{
   public class AlertViewController: Activity
   {
       public AlertViewController ()
       {
       }

        public void ShowAlertBox (string titleTxt, string messageTxt)
        {

           AlertDialog.Builder builder = new AlertDialog.Builder(this);
           builder.SetTitle(titleTxt);
           builder.SetMessage(messageTxt);
           builder.SetCancelable(false);
           builder.SetPositiveButton("OK", delegate { Finish(); });
           RunOnUiThread (() => {
            builder.Show();
           } );
       }
     }
  }

To call it from other class

AlertViewController alertView = new AlertViewController ();
alertView.ShowAlertBox ("Test", "Test");

It is crashing at the line. It throws Null Pointer Exception

 AlertDialog.Builder builder = new AlertDialog.Builder(this);

Answer 1

public class AlertViewController: Activity

AlertViewController extends Activity...hence your AlertViewController acts as a activity so it should be registered in the manifest and it should also be started using intent...later using theme to convert it into dialog...OR

One Solution just create a simple class as

public class AlertViewController

And in Constructor pass the activity context

AlertViewController alertView = new AlertViewController (YourActivity.this);
alertView.ShowAlertBox ("Test", "Test");

Another Solution extend Dialog class and create custom dialog

public class AlertViewController : Dialog

or else you can go for dialog fragments as well...for more info check http://javatechig.com/xamarin/alertdialog-and-dialogfragment-example-in-xamarin-android