如何根据显示的MDBottomNavigationItem更改MDToolbar的标题

<com.google.android.material.appbar.MaterialToolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    app:title="默认标题" />

MaterialToolbar toolbar = findViewById(R.id.toolbar);
toolbar.setTitle("新标题");

MaterialToolbar toolbar = findViewById(R.id.toolbar);
int selectedItem = bottomNavigation.getSelectedItemId();

switch (selectedItem) {
    case R.id.item1:
        toolbar.setTitle("选项1");
        break;
    case R.id.item2:
        toolbar.setTitle("选项2");
        break;
    // 添加更多的选项...
}