AndroidでAlertを表示する.

xxxActivityクラスのフィールド変数として宣言

AlertDialog.Builder builder;

xxxActivity.onCreate関数内で

builder = new AlertDialogBuilder(this);

必要なときに

builder.setTitle("Network Error")
     .setMessage("Cloud was down")
     .setPositiveButton("OK", new DialogInterface.OnClickListener() {
          @Override
          public void onClick(DialogInterface dialog, int which) {
                         // TODO Auto-generated method
          }
      });
AlertDialog alertDialog = builder.create();
alertDialog.show();