问如何检查对话框是否打开？

EN

public static void showDialog(Context context) {
    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle("Title");
    builder.setMessage("Message");
    builder.setPositiveButton("ok", new OnClickListener() {
            public void onClick(DialogInterface dialog, int arg1) {
                dialog.dismiss();
            }});
    builder.setCancelable(false);
    builder.create().show();
}