（原创）自定义一个滚屏的RecyclerView

效果展示

RecyclerView可以自己定制成想要的各种样式
比如首页的Banner，卡片样式等等
今天来分享一个滚动的RecyclerView，先看下效果：

下面就具体讲解下如何实现

Adapter

首先是adapter，因为要实现无限滚动，所以在getItemCount方法返回Integer.MAX_VALUE
具体代码如下：

public class AutoPollAdapter extends RecyclerView.Adapter {
    

    /** * 事件回调监听 */

    private OnItemClickListener onItemClickListener;

    private Context context;

    private List<AutoBean> listBeans;

    public AutoPollAdapter(Context context, List<AutoBean> listBeans) {
    
        this.context = context;
        this.listBeans = listBeans;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    
        // 实例化展示的view
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_auto_poll, parent, false);

        // 实例化viewholder
        ViewHolder viewHolder = new ViewHolder(view);
        viewHolder.imgHead = view.findViewById(R.id.img_head);
        viewHolder.tvName = view.findViewById(R.id.tv_name);
        return viewHolder;
    }



    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
    
        ViewHolder holder1 = (ViewHolder) holder;
        holder1.tvName.setText(listBeans.get(position % listBeans.size()).tvname);
        Glide.with(context).load(listBeans.get(position % listBeans.size()).url).into(holder1.imgHead);
        holder1.tvName.setOnClickListener(new View.OnClickListener() {
    
            @Override
            public void onClick(View v) {
    
                onItemClickListener.onItemClick((position % listBeans.size()));
                }
        });
    }


    @Override
    public int getItemCount() {
    
        //主要在这，实现无线轮播效果
        return Integer.MAX_VALUE;
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
    
        TextView tvName;
        ImageView imgHead;

        public ViewHolder(View itemView) {
    
            super(itemView);
        }
    }

    /** * 设置回调监听 * * @param listener */

    public void setOnItemClickListener(OnItemClickListener listener) {
    

        this.onItemClickListener = listener;

    }

    public interface OnItemClickListener {
    

        void onItemClick(int position);

    }

}

相关的xml也bean也贴上：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:orientation="horizontal" android:gravity="center_vertical" android:layout_height="60dp">

    <ImageView android:id="@+id/img_head" android:layout_width="56dp" android:layout_height="56dp" android:src="@drawable/ic_launcher" />

    <TextView android:id="@+id/tv_name" android:text="测试" android:layout_marginLeft="10dp" android:layout_width="match_parent" android:layout_height="wrap_content" />


</LinearLayout>

public class AutoBean {
    
    String tvname;
    String url;

    public AutoBean(String tvname, String url) {
    
        this.tvname = tvname;
        this.url = url;
    }

}

自定义的LinearLayoutManager

自定义一个layoutManager，去控制滑动的速度：

public class ScrollSpeedLinearLayoutManger extends LinearLayoutManager {
    

    private float MILLISECONDS_PER_INCH = 0.03f;

    private Context contxt;


    public ScrollSpeedLinearLayoutManger(Context context) {
    

        super(context);

        this.contxt = context;
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
    

        LinearSmoothScroller linearSmoothScroller =
                new LinearSmoothScroller(recyclerView.getContext()) {
    
                    @Override
                    public PointF computeScrollVectorForPosition(int targetPosition) {
    
                        return ScrollSpeedLinearLayoutManger.this
                                .computeScrollVectorForPosition(targetPosition);
                    }

                    @Override
                    protected float calculateSpeedPerPixel

                            (DisplayMetrics displayMetrics) {
    

                        setSpeedSlow();

                        return MILLISECONDS_PER_INCH / displayMetrics.density;
// return 7;
                        // 返回滑动一个pixel需要多少毫秒
                    }
                };

        linearSmoothScroller.setTargetPosition(position);

        startSmoothScroll(linearSmoothScroller);

    }

    public void setSpeedSlow() {
    

        //自己在这里用density去乘，希望不同分辨率设备上滑动速度相同

        //0.3f是自己估摸的一个值，可以根据不同需求自己修改

        MILLISECONDS_PER_INCH = contxt.getResources().getDisplayMetrics().density * 3f;

    }

    public void setSpeedFast() {
    

        MILLISECONDS_PER_INCH = contxt.getResources().getDisplayMetrics().density * 0.03f;

    }

}

自定义的RecyclerView

然后贴上自己的RecyclerView：

public class AutoPollRecyclerView extends RecyclerView {
    

    private static final long TIME_AUTO_POLL_1 = 2000;

    AutoPollTask autoPollTask;

    private int index = 2;//这个值很重要，动画先滑动到第几个

    private boolean running; //标示是否正在自动轮询

    private boolean canRun;//标示是否可以自动轮询,可在不需要的是否置false

    public AutoPollRecyclerView(Context context, @Nullable AttributeSet attrs) {
    

        super(context, attrs);

        autoPollTask = new AutoPollTask(this);
    }


    /*** * 一次只能滑一个item（轮播图） */

    static class AutoPollTask implements Runnable {
    

        private final WeakReference<AutoPollRecyclerView> mReference;

        //使用弱引用持有外部类引用->防止内存泄漏

        public AutoPollTask(AutoPollRecyclerView reference) {
    

            this.mReference = new WeakReference<AutoPollRecyclerView>(reference);

        }

        @Override
        public void run() {
    

            AutoPollRecyclerView recyclerView = mReference.get();

            if (recyclerView != null && recyclerView.running && recyclerView.canRun) {
    

                recyclerView.smoothScrollToPosition(++recyclerView.index);

                recyclerView.postDelayed(recyclerView.autoPollTask, TIME_AUTO_POLL_1);

            }

        }

    }

    //开启:如果正在运行,先停止->再开启
    public void start() {
    
        if (running)
            stop();
        canRun = true;
        running = true;
        postDelayed(autoPollTask, TIME_AUTO_POLL_1);

    }

    public void stop() {
    

        running = false;

        removeCallbacks(autoPollTask);

    }



    // 实现渐变效果
    Paint mPaint;

    private int layerId;

    private LinearGradient linearGradient;

    /** * 禁止滑动 * @param e * @return */
    public boolean onTouchEvent(MotionEvent e) {
    
        return true;
    }
    /** * 禁止滑动 * @param e * @return */
    @Override
    public boolean onInterceptTouchEvent(MotionEvent e) {
    
        return false;
    }

    private int preWidth = 0;// Recyclerview宽度动态变化时，监听每一次的宽度

    public void doTopGradualEffect(final int itemViewWidth) {
    

        mPaint = new Paint();

        // dst_in 模式，实现底层透明度随上层透明度进行同步显示（即上层为透明时，下层就透明，并不是上层覆盖下层)

        final Xfermode xfermode = new PorterDuffXfermode(PorterDuff.Mode.DST_IN);

        mPaint.setXfermode(xfermode);

        addItemDecoration(new RecyclerView.ItemDecoration() {
    

            @Override

            public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
    
                super.onDrawOver(canvas, parent, state);
                // 当linearGradient为空即第一次绘制 或 Recyclerview宽度发生改变时，重新计算透明位置
                if (linearGradient == null || preWidth != parent.getWidth()) {
    
                    // 透明位置从最后一个 itemView 的一半处到 Recyclerview 的最右边
                    linearGradient = new LinearGradient(parent.getWidth() - (itemViewWidth / 2), 0.0f, parent.getWidth(), 0.0f, new int[]{
    Color.BLACK, 0}, null, Shader.TileMode.CLAMP);
                    preWidth = parent.getWidth();
                }

                mPaint.setXfermode(xfermode);

                mPaint.setShader(linearGradient);

                canvas.drawRect(0.0f, 0.0f, parent.getRight(), parent.getBottom(), mPaint);

                mPaint.setXfermode(null);
                canvas.restoreToCount(layerId);

            }

            @Override

            public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
    

                super.onDraw(c, parent, state);
                // 此处 Paint的参数这里传的null， 在传入 mPaint 时会出现第一次打开黑屏闪现的问题
                // 注意 saveLayer 不能省也不能移动到onDrawOver方法里
                layerId = c.saveLayer(0.0f, 0.0f, (float) parent.getWidth(), (float) parent.getHeight(), null, Canvas.ALL_SAVE_FLAG);
            }

            @Override

            public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    
                super.getItemOffsets(outRect, view, parent, state);

            }

        });

    }

}

这里要注意一点，因为我们的滚屏，是不想让他可以通过手指去滑动的
也就是禁用RecyclerView的手指滑动
一般解决方案是重写layoutManager的两个方法：
canScrollVertically和canScrollHorizontally
返回false，分别禁用左右滑动和上下滑动
但这样会带来一个新的问题：
RecyclerVIew使用这个方法禁止滑动后，通过smoothScrollToPosition滑动到指定item的方法也失效了
这样自动滚屏效果就没了
我这边没用这个方法，用的是重写RecyclerView的下面两个方法：

    /** * 禁止滑动 * @param e * @return */
    public boolean onTouchEvent(MotionEvent e) {
    
        return true;
    }
    /** * 禁止滑动 * @param e * @return */
    @Override
    public boolean onInterceptTouchEvent(MotionEvent e) {
    
        return false;
    }

所以如果要打开手指滑动，注释这两个方法，然后记录监听滑动到的位置，重新设置自动滑动（这点很重要）
这个大家可以自己去实现

使用

最后，贴上使用的代码：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.example.mydemo.recy.AutoPollRecyclerView
        android:id="@+id/recycleView"
        android:fadingEdge="vertical"
        android:scrollbars="none"
        android:fadingEdgeLength="10dp"
        android:layout_width="match_parent"
        tools:listitem="@layout/item_auto_poll"
        android:layout_height="180dp"/>


</FrameLayout>

public class MainActivity extends AppCompatActivity {
    

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_recy);
        ScrollSpeedLinearLayoutManger layoutManager = new ScrollSpeedLinearLayoutManger(this);

        layoutManager.setSmoothScrollbarEnabled(true);

        layoutManager.setAutoMeasureEnabled(true);
        AutoPollRecyclerView recyclerView = findViewById(R.id.recycleView);

        recyclerView.setLayoutManager(layoutManager);// 布局管理器。
        recyclerView.setHasFixedSize(true);// 如果Item够简单，高度是确定的，打开FixSize将提高性能。
        recyclerView.setItemAnimator(new DefaultItemAnimator());// 设置Item默认动画，加也行，不加也行。
        ArrayList<AutoBean> list = new ArrayList<>();
        list.add(new AutoBean("哆啦A梦","https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fup.enterdesk.com%2Fedpic_source%2F91%2F81%2Fd7%2F9181d7d8787f7e96f0017da5e61ad27d.jpg&refer=http%3A%2F%2Fup.enterdesk.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1659497299&t=05f317ff452b3f1a452f7e06c9ce8703"));
        list.add(new AutoBean("小狗","https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fc-ssl.duitang.com%2Fuploads%2Fitem%2F201610%2F17%2F20161017213843_EeViB.thumb.1000_0.jpeg&refer=http%3A%2F%2Fc-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1659497393&t=6f8f90c5b409231ef5902aafc7464d31"));
        list.add(new AutoBean("卡通头像","https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fc-ssl.duitang.com%2Fuploads%2Fblog%2F202107%2F09%2F20210709142454_dc8dc.thumb.1000_0.jpeg&refer=http%3A%2F%2Fc-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1659497417&t=1a38f19555bcb59f5f9e127126fba84a"));
        list.add(new AutoBean("火影头像","https://gimg2.baidu.com/image_search/src=http%3A%2F%2Finews.gtimg.com%2Fnewsapp_bt%2F0%2F13207652291%2F1000.jpg&refer=http%3A%2F%2Finews.gtimg.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1659497813&t=a911ff64c37a57aeb95a6f31d13a573b"));
        AutoPollAdapter autoPollAdapter = new AutoPollAdapter(MainActivity.this, list);
        autoPollAdapter.setOnItemClickListener(new AutoPollAdapter.OnItemClickListener() {
    
            @Override
            public void onItemClick(int position) {
    
                Log.d("AutoPollAdapter", "点击了" + (position));
                Toast.makeText(MainActivity.this, "点击了" + (position ), Toast.LENGTH_SHORT).show();
            }
        });
        recyclerView.setAdapter(autoPollAdapter);

        recyclerView.start();
        DisplayMetrics dm = getResources().getDisplayMetrics();
        recyclerView.doTopGradualEffect(dm.widthPixels);

    }
}

最后注意一点：
如果要recycleview里面显示的item数量为整数
比如就显示三个，
那么recycleview的高度，一定要设置成item的高度的整倍数
比如三倍，就代表可以显示三个item，五倍就显示五个。