我有以下几点AlertDialog。

showDialog(
            context: context,
            child: new AlertDialog(
              title: const Text("Location disabled"),
              content: const Text(
                  """
Location is disabled on this device. Please enable it and try again.
                  """),
              actions: [
                new FlatButton(
                  child: const Text("Ok"),
                  onPressed: _dismissDialog,
                ),
              ],
            ),
        );

我_dismissDialog()该如何解雇说AlertDialog？