BottomNavigationView hides when scrolling up instead of down

问题

The new BottomNavigationView from support library v25.0.0 is supposed to hide when scrolling down, in order to see all the items from a list. However, in my testing scenario, the view hides when scrolling up. Any ideas what can cause this reverse behavior?

The inner_fragment is set up as a Fragment inserted inside the activity_main_framelayout_content Framelayout. XML layouts below:

main_activity.xml:

<android.support.design.widget.CoordinatorLayout
        android:id="@+id/activity_main_coordinatorlayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
            android:id="@+id/activity_main_appbarlayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
                android:id="@+id/activity_main_toolbar"
                android:layout_height="?attr/actionBarSize"
                android:layout_width="match_parent"
                android:background="?attr/colorPrimary"
                app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
                app:layout_scrollFlags="scroll|enterAlways">

            <include layout="@layout/activity_main_spinner_layout"/>
        </android.support.v7.widget.Toolbar>
    </android.support.design.widget.AppBarLayout>

    <FrameLayout
            android:id="@+id/activity_main_framelayout_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            android:fitsSystemWindows="true"/>
</android.support.design.widget.CoordinatorLayout>

<android.support.design.widget.NavigationView
        android:id="@+id/activity_main_framelayout_navigation_drawer"
        android:layout_width="@dimen/drawer_width"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"
        android:background="@color/color_black_700"/>

inner_fragment.xml:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:app="http://schemas.android.com/apk/res-auto"
             android:layout_width="match_parent"
             android:layout_height="match_parent">

    <FrameLayout
            android:id="@+id/inner_fragment_framelayout"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

    <android.support.design.widget.BottomNavigationView
            android:id="@+id/inner_fragment_bottom_navigation_view"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            app:menu="@menu/inner_fragment"
            app:itemBackground="@drawable/bg_bottom_navigation"
            app:itemIconTint="@color/ic_bottom_navigation"
            app:itemTextColor="@color/ic_bottom_navigation"/>
</FrameLayout>

回答1:

This release of BottomNavigationView is missing scrolling behavior to work out of the box as specified in the guidelines.

I wrote an article on what's missing and how you can fix it. This includes implementing scrolling behavior of the BottomNavigationView in CoordinatorLayout.

回答2:

A simple solution is to just add an offset listener to appbarlayout. Works perfectly for me.

So something like this:

((AppBarLayout)toolbar.getParent()).addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
        mNavigationBar.setTranslationY(verticalOffset*-1);
    }
});

回答3:

My solution was to replace the FrameLayout with a NestedCoordinatorLayout from here https://stackoverflow.com/a/37660246/2233621 and then add the BottomNavigationBehavior from Nikola's blog post https://medium.com/@nullthemall/bottomnavigationview-missing-pearls-eaa950f9ad4e#.p1i01wwui that way your bottom navigation behaviour can listen for nested scrolling of the fragment inside the NestedCoordinatorLayout

I believe you could use another view that implements NestedScrollParent + NestedScrollChild for the same behaviour.

来源：https://stackoverflow.com/questions/40171801/bottomnavigationview-hides-when-scrolling-up-instead-of-down