我如何“交换UI片段”？

Question

我已经实现了Android导航抽屉。它工作正常，除了我无法加载我的片段。我应该在// Add code here to update the UI based on the item selected // For example, swap UI fragments here下输入什么代码？

我构建的片段与导航抽屉中的每个项目相对应。如何加载这些相应的片段？

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    ActionBar actionbar = getSupportActionBar();
    actionbar.setDisplayHomeAsUpEnabled(true);
    actionbar.setHomeAsUpIndicator(R.drawable.ic_menu);

    mDrawerLayout = findViewById(R.id.drawer_layout);

    NavigationView navigationView = findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(
            new NavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(MenuItem menuItem) {
                    // set item as selected to persist highlight
                    menuItem.setChecked(true);
                    // close drawer when item is tapped
                    mDrawerLayout.closeDrawers();

                    // Add code here to update the UI based on the item selected
                    // For example, swap UI fragments here

                    return true;
                }
            });

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            mDrawerLayout.openDrawer(GravityCompat.START);
            return true;
    }
    return super.onOptionsItemSelected(item);
}
}