Question

我在滚动视图时遇到了一种非常奇怪的行为。片段＆＃34; A＆＃34;使用RecyclerView和Fragment＆＃34; B＆＃34;使用listView。

对于Recycler视图，我使用以下代码：

list.setOnScrollListener(new RecyclerView.OnScrollListener() {
        int mLastFirstVisibleItem = 0;

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        }

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            final int currentFirstVisibleItem = linearLayoutManager.findFirstVisibleItemPosition();

            if (currentFirstVisibleItem > this.mLastFirstVisibleItem) {
                ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
            } else if (currentFirstVisibleItem < this.mLastFirstVisibleItem) {
                ((AppCompatActivity)getActivity()).getSupportActionBar().show();
            }

            this.mLastFirstVisibleItem = currentFirstVisibleItem;
        }
    });

对于ListView，我使用以下代码：

list.setOnScrollListener(new AbsListView.OnScrollListener() {
        int mLastFirstVisibleItem = 0;

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {   }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            if (view.getId() == list.getId()) {
                final int currentFirstVisibleItem = list.getFirstVisiblePosition();

                if (currentFirstVisibleItem > mLastFirstVisibleItem) {
                    // getSherlockActivity().getSupportActionBar().hide();
                    ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
                } else if (currentFirstVisibleItem < mLastFirstVisibleItem) {
                    // getSherlockActivity().getSupportActionBar().show();
                    ((AppCompatActivity)getActivity()).getSupportActionBar().show();
                }

                mLastFirstVisibleItem = currentFirstVisibleItem;
            }
        }
    });

以下是GIF，所以，基本上，我滚动并按住它并且不要释放我的手指，我会得到以下行为。

Answer 1

如果您正在寻找的appBar行为类似于WhatsApp，我认为更好的方法是从您的布局而不是Java中控制appBar行为。下面是一个如何为包含RecyclerView的片段和包含ListView的片段执行此操作的示例：

<强> activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    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">

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

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_collapseMode="pin"
            app:layout_scrollFlags="scroll|enterAlways|snap"/>

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

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</android.support.design.widget.CoordinatorLayout>

<强> fragmenta.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rec_fragmenta"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:splitMotionEvents="false"
        android:clipToPadding="false"/>

</android.support.design.widget.CoordinatorLayout>

<强> fragmentb.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <ListView
        android:id="@+id/list_fragmentb"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:nestedScrollingEnabled="true"/>

</android.support.design.widget.CoordinatorLayout>

<强> MainActivity.java

public class MainActivity extends AppCompatActivity {

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

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tablayout);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        SectionsPagerAdapter mSectionsPagerAdapter = new 
        SectionsPagerAdapter(getSupportFragmentManager());
        ViewPager mViewPager = (ViewPager) findViewById(R.id.viewpager);
        tabLayout.setupWithViewPager(mViewPager);
        mViewPager.setAdapter(mSectionsPagerAdapter);
    }


    private class SectionsPagerAdapter extends FragmentPagerAdapter {

        private SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
                case 0:
                    return new FragmentA();
                case 1:
                    return new FragmentB();
                case 2:
                    return new FragmentC();
            }
            return null;
        }

        @Override
        public int getCount() {
            return 3;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            switch (position) {
                case 0:
                    return "A";
                case 1:
                    return "B";
                case 2:
                    return "C";
            }
            return null;
        }
    }
}

<强> FragmentA

public class FragmentA extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragmenta, container, false);
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        RecyclerView recyclerView = rootView.findViewById(R.id.rec_fragmenta);
        recyclerView.setLayoutManager(layoutManager);
        List<String> list = getList();
        MyListAdapter adapter = new MyListAdapter(list);
        recyclerView.setAdapter(adapter);
        return rootView;
    }
}

<强> FragmentB

public class FragmentB extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragmentb, container, false);
        ListView listView = rootView.findViewById(R.id.list_fragmentb);
        List<String> list = getList();
        ArrayAdapter<String> adapter = new ArrayAdapter<>(getActivity(),
                android.R.layout.simple_list_item_1, android.R.id.text1, list);
        listView.setAdapter(adapter);
        return rootView;
    }
}

Answer 2

隐藏Toolbar后，ListView＆amp; RecyclerView被扩展到顶部，再次显示第一个项目，因此再次显示Toolbar。

您应该检查变量dy是正面还是负面;如果dy为肯定，则用户向上滚动，否则向下滚动。如果我们采用这个代码就变成这样：

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);
    final int currentFirstVisibleItem = linearLayoutManager.findFirstVisibleItemPosition();

    if (currentFirstVisibleItem > this.mLastFirstVisibleItem && dy > 0) {
        ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
    } else if (currentFirstVisibleItem < this.mLastFirstVisibleItem && dy < 0) {
        ((AppCompatActivity)getActivity()).getSupportActionBar().show();
    }

    this.mLastFirstVisibleItem = currentFirstVisibleItem;
}

或者你可以忽略firstVisibleItem之类的属性，也可以使用dy（如果你真的不需要检查第一项是否显示）：

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);

    if (dy > 0) {
        ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
    } else if (dy < 0) {
        ((AppCompatActivity)getActivity()).getSupportActionBar().show();
    }
}

隐藏Action Bar时，ListView和RecyclerView中的奇怪滚动行为

2 个答案: