android - Androidでメッセージボックスを正しく追加する方法

Question

メソッドで構文エラーが発生しました

setPositiveButton(String, new DialogInterface.OnClickListener(){}) : is undefined for the type AlertDialog

それを解決する方法?

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AlertDialog alertDialog = null;
alertDialog = new AlertDialog.Builder(MainActivity.this).create();
alertDialog.setTitle("error msg");
alertDialog.setMessage("You should register before");
alertDialog.setCancelable(true);
alertDialog.setPositiveButton("Ok",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
//dismiss the dialog  
 }
}); 

alertDialog.show();

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