使用 ViewPager 在选项卡之间切换时，RecyclerView 一次自动滚动一项

Question

我有一个基本的布局设置：DrawerLayout，它由活动的主布局和导航视图的布局组成。主布局有一个 CoordinatorLayout 和实现折叠工具栏功能所需的所有布局，以及一个 ViewPager，我稍后在代码中用片段填充它。Fragment 的布局主要由 RecyclerView 和其他次要视图组成。

问题如下：每当我向下滚动两个选项卡中的任何一个并滑动到新选项卡并返回到原始选项卡时，RecyclerView 都会收到 onScrolled 回调（它不应该收到，因为我还没有滚动RV 本身，但 ViewPager）具有负 deltaY 参数（这意味着方向向上），这会导致顶部的下一个项目变得可见。

一些注意事项：

• deltaY 参数似乎总是等于下一个项目距顶部的高度（这给人的印象是，只要整个过程发生，RV 就会向上滚动一个项目）
• 我没有将 OnPageChangeListener 设置为 ViewPager，以便在页面滚动、选择或状态更改时收到通知。
• 我向片段的 RecyclerView 提供 RecyclerViewScrollListener，以便在 RV 滚动以执行某些逻辑时收到通知（例如将此事件传播到活动以显示或隐藏浮动操作按钮）
• 我已经制作了调用 onScrolled 时的调用堆栈的屏幕截图。也许有人会发现它有用。看一看。
• 我还制作了一个代表这种行为的短视频。看一看。
• 我在网上查了很多资源，但没有一个能帮助我解决这个问题。随意问任何问题。任何帮助将非常感激。

仪表板_activity_layout.xml：

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/coordinatorLayout"
    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:elevation="@dimen/toolbar_shadow_height">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="@dimen/toolbar_height"
            android:paddingTop="@dimen/toolbar_padding_top"
            app:layout_scrollFlags="scroll|enterAlwaysCollapsed"
            app:titleTextAppearance="@style/TitleTextView"
            tools:background="@color/colorPrimary"/>

        <android.support.design.widget.TabLayout
            android:id="@+id/tabLayout"
            android:layout_width="match_parent" 
            android:layout_height="@dimen/dashboard_activity_content_tab_layout_height"
            app:tabMode="fixed"
            app:tabGravity="fill"
            tools:background="@color/colorPrimary"/>

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

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:overScrollMode="never"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:background="@color/colorPrimaryDark"/>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/actionButtonFab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/dashboard_activity_content_fab_margin"
        android:layout_gravity="bottom|end"
        android:src="@mipmap/ic_search_white_24dp"
        app:fabSize="normal"
        app:useCompatPadding="true"
        tools:backgroundTint="@color/colorAccent"/>

DashboardActivity.java（相关部分）：

private void initViewPager() {
    mViewPager = findViewById(R.id.viewPager);

    mAdapter = new DashboardViewPagerAdapter(getSupportFragmentManager());
    mAdapter.setViewPagerId(mViewPager.getId());
    mAdapter.setRecyclerViewStateListener(mRecyclerViewStateListener);

    populateAdapter();

    mViewPager.setAdapter(mAdapter);
    mViewPager.setOffscreenPageLimit(mAdapter.getCount());
}


private void populateAdapter() {
    BaseFragment baseFragment = mAdapter.getFragmentForPosition(TAB_TAB_1);

    if(baseFragment == null) {
        baseFragment = SomeFragment.newInstance(Common.SOME_TYPE_1);
    }

    mAdapter.addFragment(baseFragment);

    baseFragment = mAdapter.getFragmentForPosition(TAB_TAB_2);

    if(baseFragment == null) {
        baseFragment = SomeFragment.newInstance(Common.SOME_TYPE_2);
    }

    mAdapter.addFragment(baseFragment);

    baseFragment = mAdapter.getFragmentForPosition(TAB_TAB_3);

    if(baseFragment == null) {
        baseFragment = SomeOtherFragment.init();
    }

    mAdapter.addFragment(baseFragment);
}


private RecyclerViewStateListener mRecyclerViewStateListener = new RecyclerViewStateListener() {


    @Override
    public void onScrolledDownwards(RecyclerView recyclerView, int deltaY) {
        // Hiding the FAB by animating it
        DashboardCommon.hideActionButton(mActionButtonFab, mViewAnimator, true);
    }


    @Override
    public void onScrolledUpwards(RecyclerView recyclerView, int deltaY) {
        // Showing the FAB by animating it
        DashboardCommon.showActionButton(mActionButtonFab, mViewAnimator, true);
    }


};

SomeFragment.java（相关部分）：

private void initRecyclerView() {
    mRecyclerView = findViewById(R.id.recyclerView);
    mRecyclerView.addOnScrollListener(new RecyclerViewScrollListener(this));

    mLayoutManager = new LinearLayoutManager(
        getContext(),
        LinearLayoutManager.VERTICAL,
        false
    );
    mRecyclerView.setLayoutManager(mLayoutManager);

    mAdapter = new SomeRecyclerViewAdapter(getContext(), mItems);

    mRecyclerView.setAdapter(mAdapter);
}


// mRecyclerViewStateListener is the listener passed from the
// DashboardActivity


@CallSuper
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onScrollStateChanged(recyclerView, newState);
    }
}




@Override
public void onScrolled(RecyclerView recyclerView, int deltaX, int deltaY) {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onScrolled(recyclerView, deltaX, deltaY);
    }
}




@Override
public void onScrolledDownwards(RecyclerView recyclerView, int deltaY) {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onScrolledDownwards(recyclerView, deltaY);
    }
}




@Override
public void onScrolledUpwards(RecyclerView recyclerView, int deltaY) {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onScrolledUpwards(recyclerView, deltaY);
    }
}




@Override
public void onBottomReached() {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onBottomReached();
    }
}




@Override
public void onMidpointReached(int direction) {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onMidpointReached(direction);
    }
}




@Override
public void onTopReached() {
    if(mRecyclerViewStateListener != null) {
        mRecyclerViewStateListener.onTopReached();
    }
}

RecyclerViewScrollListener.java（相关部分）：

public class RecyclerViewScrollListener extends RecyclerView.OnScrollListener {


    public static final int DIRECTION_UNSPECIFIED = -1;
    public static final int DIRECTION_UPWARDS = 0;
    public static final int DIRECTION_DOWNWARDS = 1;

    // Omitted...

    private StateListener mStateListener;




    public RecyclerViewScrollListener(StateListener stateListener) {
        // Omitted..

        mStateListener = stateListener;
    }




    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        if(mStateListener != null) {
            mStateListener.onScrollStateChanged(recyclerView, newState);
        }
    }




    @Override
    public void onScrolled(RecyclerView recyclerView, int deltaX, int deltaY) {
        if(mStateListener != null) {
            mStateListener.onScrolled(recyclerView, deltaX, deltaY);
        }

        f(deltaY > 0) {
            // Recycler view's contents are moving downwards

            // Notifying about the downwards scroll
            if(mStateListener != null) {
                mStateListener.onScrolledDownwards(recyclerView, deltaY);
            }

            // Omitted...

            if(someConditionIsTrue) {
                // Omitted...

                // Notifying the listener
                mStateListener.onBottomReached();
            } else if((someOtherConditionIsTrue) {
                mStateListener.onMidpointReached(DIRECTION_DOWNWARDS);
            }
        } else if(deltaY < 0) {
            // Recycler view's contents are moving upwards

            // Notifying about upwards scroll
            if(mStateListener != null) {
                mStateListener.onScrolledUpwards(recyclerView, deltaY);
            }

            // Omitted...

            if(someConditionIsTrue) {
                // Omitted..

                // Notifying the listener
                mStateListener.onTopReached();
            } else if(someOtherConditionIsTrue) {
                mStateListener.onMidpointReached(DIRECTION_UPWARDS);
            }
        }
    }




    public interface StateListener {

        void onScrollStateChanged(RecyclerView recyclerView, int newState);

        void onScrolled(RecyclerView recyclerView, int deltaX, int deltaY);

        void onScrolledDownwards(RecyclerView recyclerView, int deltaY);

        void onScrolledUpwards(RecyclerView recyclerView, int deltaY);

        void onBottomReached();

        void onMidpointReached(int direction);

        void onTopReached();

    }




}

Answer 1

使用此滚动自动一次滚动一项

RecyclerView my_recycler_view= (RecyclerView) findViewById(R.id.my_recycler_view);
SnapHelper snapHelper = new PagerSnapHelper();
snapHelper.attachToRecyclerView(my_recycler_view);

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