导航到其他片段时如何在滚动后显示底部应用栏？

Question

我已经在我的应用程序中实现了底部应用栏。我可以在滚动时隐藏底部应用栏，但是当我导航到其他片段时它仍然隐藏？如何以编程方式使底部应用栏可见？

根据 Material Design Documentation，我在底部应用栏中定义了以下属性。

app:hideOnScroll="true"

在 Fragment 中，我将滚动内容放在 NestedScrollView 中，如下所示：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".Admin.AddUpdateCustomerFragment"
    android:orientation="vertical"
    android:transitionName="transtion_name_example"
    >

    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:id="@+id/linearLayout">


        </LinearLayout>
    </androidx.core.widget.NestedScrollView>
</LinearLayout>

AdminActivity.java

public class AdminActivity extends AppCompatActivity {
    public BottomAppBar bottomAppBar;
    public FloatingActionButton floatingActionButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_admin);
        getWindow().setEnterTransition(null);
        floatingActionButton = (FloatingActionButton) findViewById(R.id.fab);
        bottomAppBar = (BottomAppBar) findViewById(R.id.bar);
        setSupportActionBar(bottomAppBar);
        new CustomerFragment().setArguments(Bundle.EMPTY);

        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.fragment_container, new CustomerFragment())
                .commit();
    }

    public boolean loadFragment(Fragment fragment, Bundle bundle) {
        if (fragment != null) {
            fragment.setArguments(bundle);
            getSupportFragmentManager()
                    .beginTransaction()
                    .replace(R.id.fragment_container, fragment)
                    .commit();

            return true;
        }
        return false;
    }
}

CustomerFragment.java

public class CustomerFragment extends Fragment {
    View rootView;

    public CustomerFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        rootView = inflater.inflate(R.layout.fragment_customer_fragment_admin, container, false);

        ((AdminActivity) getActivity()).bottomAppBar.setFabAlignmentMode(BottomAppBar.FAB_ALIGNMENT_MODE_CENTER);
        ((AdminActivity) getActivity()).floatingActionButton.setImageResource(R.drawable.ic_add_black_24dp);
        ((AdminActivity) getActivity()).floatingActionButton.setColorFilter(Color.WHITE);

        ((AdminActivity) getActivity()).floatingActionButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ((AdminActivity) getActivity()).loadFragment(new AddUpdateCustomerFragment(), Bundle.EMPTY);
            }
        });
        return rootView;
    }

AddUpdateCustomerFragment.java

public class AddUpdateCustomerFragment extends Fragment {
    View rootView;

    public AddUpdateCustomerFragment() {
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        rootView =  inflater.inflate(R.layout.fragment_add_update_customer, container, false);

        ((AdminActivity) getActivity()).bottomAppBar.setNavigationIcon(null);
        ((AdminActivity) getActivity()).bottomAppBar.setFabAlignmentMode(FAB_ALIGNMENT_MODE_END);

        btnBack = (ImageView) rootView.findViewById(R.id.back);

        btnBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ((AdminActivity) getActivity()).loadFragment(new CustomerFragment(), Bundle.EMPTY);
            }
        });
        return rootView;
    }
}

Answer 1

这里有一个解决您的问题的方法。

将OnScrollChangeListener 附加到您的NestedScrollView 以切换BottomNavBar 的可见性

scroller.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
    @Override
    public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {

        if (scrollY > oldScrollY) {
            Log.i(TAG, "Scroll DOWN");
            mBottomNavBar.setVisibility(View.GONE);
        }
        if (scrollY < oldScrollY) {
            Log.i(TAG, "Scroll UP");
            mBottomNavBar.setVisibility(View.VISIBLE);
        }

        if (scrollY == 0) {
            Log.i(TAG, "TOP SCROLL");
        }

       if (scrollY == ( v.getChildAt(0).getMeasuredHeight() - v.getMeasuredHeight() )) {
           Log.i(TAG, "BOTTOM SCROLL");
       }
   }
});

在片段的onCreateView() 内，切换BottomNavigationBar 的Visibility 并隐藏它。

@Override
protected void onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    //...
    bottomNavBar.setVisibility(View.VISIBLE)
}

或在启动新的Fragment 时执行相同操作：

 btnBack.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            ((AdminActivity) getActivity()).loadFragment(new CustomerFragment(), Bundle.EMPTY);
            mBottomNavBar.setVisibility(View.VISIBLE);
        }
    });

别忘了删除 app:hideOnScroll="true"