RecyclerView实现类似ViewPager翻页OnPageChangeListener监听功能

转载请注明：https://blog.csdn.net/u012854870/article/details/84984066

我们在使用ViewPager的时候多多少少都会遇到一些坑，这里今天就不细说了。

首先我们先介绍一下SnapHelper

Google 在 Android 24.2.0 的support 包中添加了SnapHelper,SnapHelper是对RecyclerView的拓展，结合RecyclerView使用，能很方便的做出一些炫酷的效果。SnapHelper到底有什么功能呢？SnapHelper旨在支持RecyclerView的对齐方式，也就是通过计算对齐RecyclerView中TargetView 的指定点或者容器中的任何像素点。

接下来介绍一下SnapHelper的两个子类，LinearSnapHelper和PagerSnapHelper，我们要实现ViewPaper就需要用到其中的某一个

(1) LinearSnapHelper
LinearSnapHelper 使当前Item居中显示，类似ViewPager效果，但是又可以快速滑动（滑动多页）。代码如下

 LinearSnapHelper linearSnapHelper = new LinearSnapHelper();
 //将SnapHelper attach 到RecyclrView
 linearSnapHelper.attachToRecyclerView(recyclerView);

2) PagerSnapHelper (在Android 25.1.0 support 包加入的)
PagerSnapHelper的展示效果和LineSnapHelper是一样的，只是PagerSnapHelper 限制一次只能滑动一页，不能快速滑动。代码如下：

PagerSnapHelper pagerSnapHelper = new PagerSnapHelper();
//将SnapHelper attach 到RecyclrView
pagerSnapHelper.attachToRecyclerView(recyclerView);

至此我们可以根据自己的需求选择合适的SnapHelper实现ViewPager翻页效果。

接下来进入今天的主题RecyclerView添加翻页监听功能

ViewPager本身帮我们实现了OnPageChangeListener我们只需要添加就可以，而我们使用RecycleView实现的ViewPager效果本身是没有OnPageChangeListener事件的实现的，我们可以利用RecyclerView.OnScrollListener实现此功能。代码如下：

/**
 * Created by pangli on 2018/12/13 9:43
 * 备注：RecyclerView实现类似ViewPager的PageChangeListener监听
 */
public class RecyclerViewPageChangeListenerHelper extends RecyclerView.OnScrollListener {
    private SnapHelper snapHelper;
    private OnPageChangeListener onPageChangeListener;
    private int oldPosition = -1;//防止同一Position多次触发

    public RecyclerViewPageChangeListenerHelper(SnapHelper snapHelper, OnPageChangeListener onPageChangeListener) {
        this.snapHelper = snapHelper;
        this.onPageChangeListener = onPageChangeListener;
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        if (onPageChangeListener != null) {
            onPageChangeListener.onScrolled(recyclerView, dx, dy);
        }
    }

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        int position = 0;
        RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
        //获取当前选中的itemView
        View view = snapHelper.findSnapView(layoutManager);
        if (view != null) {
            //获取itemView的position
            position = layoutManager.getPosition(view);
        }
        if (onPageChangeListener != null) {
            onPageChangeListener.onScrollStateChanged(recyclerView, newState);
            //newState == RecyclerView.SCROLL_STATE_IDLE 当滚动停止时触发防止在滚动过程中不停触发
            if (newState == RecyclerView.SCROLL_STATE_IDLE && oldPosition != position) {
                oldPosition = position;
                onPageChangeListener.onPageSelected(position);
            }
        }
    }

    public interface OnPageChangeListener {
        void onScrollStateChanged(RecyclerView recyclerView, int newState);

        void onScrolled(RecyclerView recyclerView, int dx, int dy);

        void onPageSelected(int position);
    }

}

至此我们就实现了RecyclerView的OnPageChangeListener功能。

使用：

        LinearSnapHelper linearSnapHelper = new LinearSnapHelper();
        linearSnapHelper.attachToRecyclerView(recyclerView);
        recyclerView.postDelayed(new Runnable() {
            @Override
            public void run() {
                recyclerView.smoothScrollToPosition(4);
            }
        }, 5000);
        recyclerView.addOnScrollListener(new RecyclerViewPageChangeListenerHelper(linearSnapHelper,
                new RecyclerViewPageChangeListenerHelper.OnPageChangeListener() {


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

                    }

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

                    }

                    @Override
                    public void onPageSelected(int position) {
                        ToastUtils.showToastShort(mContext, "选中" + position);
                        Log.e("Zorro", "选中" + position);
                    }
                }));