ActionBar中設置最右邊的overflow按鈕不顯示

private void setOverflowShowingAlways() {
    try {
        ViewConfiguration config = ViewConfiguration.get(this);
        Field menuKeyField = ViewConfiguration.class
                .getDeclaredField("sHasPermanentMenuKey");
        menuKeyField.setAccessible(true);
        menuKeyField.setBoolean(config, true);
    } catch (Exception e) {
        e.printStackTrace();
    }
}