Android RecyclerView的簡便寫法

RecyclerView如今能夠說是很經常使用了吧？RecyclerView天然是很方便的控件，但用多了有時候對一些重複性代碼也是感受挺麻煩的，因而乎我就將一些重複性代碼封裝了起來，從而使 RecyclerView 的使用更加的簡便

本篇博客包含的內容有：

1. 通用的單佈局 RecyclerView.Adapter

2. 通用的多佈局 RecyclerView.Adapter

3. 通用的 RecyclerView.ItemDecoration

4. RecyclerView 的單擊和長按事件監聽

5. 帶頭部與底部View的 RecyclerView

6. SnapHelper 的使用

1、通用的 RecyclerView.Adapter

CommonRecyclerViewAdapter 是一個抽象類，利用泛型構造了一個通用的Adapter，並經過 MultiTypeSupport 接口來實現對多佈局的支持。 此外，有時候咱們在刷新數據時，改變的數據可能只是List集合中的單個數據，若是都採用 Adapter.notifyDataSetChanged() 來刷新整個視圖，無疑是浪費資源的，此處採用了 DiffUtil 來對比先後兩個數據集，尋找出舊數據集與新數據集的最小變化量，從而對數據進行定向刷新，能夠只刷新相應的Item，使得視圖的刷新過程更爲高效，且增添和刪除數據時都伴隨有相應的動畫效果

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:50
 * 說明：通用RecyclerView Adapter
 */
public abstract class CommonRecyclerViewAdapter<T> extends RecyclerView.Adapter<CommonRecyclerViewHolder> {

    //省略一些代碼
    ......

    private DiffUtil.Callback callback = new DiffUtil.Callback() {

        @Override
        public int getOldListSize() {
            return getItemCount();
        }

        @Override
        public int getNewListSize() {
            return newDataList.size();
        }

        @Override
        public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
            return CommonRecyclerViewAdapter.this.areItemsTheSame(oldItemPosition, newItemPosition);
        }

        @Override
        public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
            return CommonRecyclerViewAdapter.this.areContentsTheSame(oldItemPosition, newItemPosition);
        }

        @Nullable
        @Override
        public Object getChangePayload(int oldItemPosition, int newItemPosition) {
            return CommonRecyclerViewAdapter.this.getChangePayload(oldItemPosition, newItemPosition);
        }
    };
    
    public void setData(final List<T> dataList) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                newDataList.clear();
                newDataList = CommonRecyclerViewAdapter.this.clone(dataList);
                DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(callback, true);
                Message message = new Message();
                message.what = DIFF_UTIL_UPDATE;
                message.obj = diffResult;
                handler.sendMessage(message);
            }
        }).start();
    }

    @Override
    public int getItemViewType(int position) {
        if (multiTypeSupport != null) {
            return multiTypeSupport.getLayoutId(dataList.get(position), position);
        }
        return DEFAULT_ITEM_VIEW_TYPE;
    }

    @Override
    public CommonRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (multiTypeSupport != null) {
            layoutId = viewType;
        }
        return new CommonRecyclerViewHolder(layoutInflater.inflate(layoutId, parent, false));
    }

    @Override
    public void onBindViewHolder(CommonRecyclerViewHolder holder, int position, List<Object> payloads) {
        if (payloads.isEmpty()) {
            onBindViewHolder(holder, position);
        } else {
            Bundle bundle = (Bundle) payloads.get(0);
            partialBindData(holder, bundle);
        }
    }

    @Override
    public void onBindViewHolder(CommonRecyclerViewHolder holder, int position) {
        entirelyBindData(holder, dataList.get(position));
        if (clickListener != null) {
            holder.setClickListener(clickListener);
        }
        if (longClickListener != null) {
            holder.setLongClickListener(longClickListener);
        }
    }

    //省略一些代碼
    ......

    private List<T> clone(List<T> dataList) {
        List<T> tempDataList = new ArrayList<>(dataList.size());
        for (T data : dataList) {
            tempDataList.add(clone(data));
        }
        return tempDataList;
    }

    /**
     * clone 指定對象，以此得到對象副本
     *
     * @param data 要複製的對象
     * @return 對象副本
     */
    protected abstract T clone(T data);

    /**
     * 判斷數據列表刷新先後指定索引的位置是否指向同一條數據
     * 此處只對比二者是否指向同一條數據，而不關心其數據內容是否有變化
     *
     * @param oldItemPosition 更新前的數據索引
     * @param newItemPosition 更新後的數據索引
     * @return 是否指向同一條數據
     */
    protected abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition);

    /**
     * 此處來判斷指向同一條數據的先後兩個索引位置，其數據內容是否相同
     * 只在 areItemsTheSame 返回 true 時纔會調用本方法
     *
     * @param oldItemPosition 更新前的數據索引
     * @param newItemPosition 更新後的數據索引
     * @return 數據內容是否有變化
     */
    protected abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition);

    /**
     * 獲取同條數據在刷新先後是哪些數據內容發生了變化
     * 只在 areContentsTheSame 返回 false 時纔會調用本方法
     *
     * @param oldItemPosition 更新前的數據索引
     * @param newItemPosition 更新後的數據索引
     * @return 數據變化內容
     */
    @NonNull
    protected abstract Bundle getChangePayload(int oldItemPosition, int newItemPosition);

    /**
     * 對刷新先後的數據進行定向更新，即只更新數據發生了變化的View
     *
     * @param holder Holder
     * @param bundle getChangePayload 方法的返回值
     */
    protected abstract void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle);

    /**
     * 對數據進行徹底綁定
     *
     * @param holder Holder
     * @param data   Data
     */
    protected abstract void entirelyBindData(CommonRecyclerViewHolder holder, T data);

}
複製代碼

此處還須要使用到一個通用的 RecyclerView.ViewHolder

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:52
 * 說明：通用RecyclerView ViewHolder
 */
public class CommonRecyclerViewHolder extends RecyclerView.ViewHolder {

    public interface OnClickListener {
        void onClick(int position);
    }

    public interface OnLongClickListener {
        void onLongClick(int position);
    }

    private OnClickListener clickListener;

    private OnLongClickListener longClickListener;

    //用來存放View以減小findViewById的次數
    private SparseArray<View> viewSparseArray;

    CommonRecyclerViewHolder(View view) {
        super(view);
        viewSparseArray = new SparseArray<>();
        view.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (clickListener != null) {
                    clickListener.onClick(getAdapterPosition());
                }
            }
        });
        view.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View v) {
                if (longClickListener != null) {
                    longClickListener.onLongClick(getAdapterPosition());
                }
                return true;
            }
        });
    }

    void setClickListener(OnClickListener clickListener) {
        this.clickListener = clickListener;
    }

    void setLongClickListener(OnLongClickListener longClickListener) {
        this.longClickListener = longClickListener;
    }

    /**
     * 根據 ID 來獲取 View
     *
     * @param viewId viewID
     * @param <T>    泛型
     * @return 將結果強轉爲 View 或 View 的子類型
     */
    private <T extends View> T getView(@IdRes int viewId) {
        // 先從緩存中找，找到的話則直接返回
        // 若是找不到則findViewById，再把結果存入緩存中
        View view = viewSparseArray.get(viewId);
        if (view == null) {
            view = itemView.findViewById(viewId);
            if (view != null) {
                viewSparseArray.put(viewId, view);
            }
        }
        return (T) view;
    }

    public CommonRecyclerViewHolder setText(@IdRes int viewId, CharSequence text) {
        TextView textView = getView(viewId);
        if (textView != null) {
            textView.setText(text);
        }
        return this;
    }

	//省略一些代碼
    ......
	
}
複製代碼

2、通用的單佈局 RecyclerView.Adapter 使用示例

先來新建一個Model

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:55
 * 說明：
 */
public class New {

    private int index;

    private String title;

    private String content;

    public New(int index, String title, String content) {
        this.index = index;
        this.title = title;
        this.content = content;
    }

    //省略一些代碼
    ......

}
複製代碼

每一個子項的佈局包含一個索引TextView、一個標題TextView、一個內容TextView

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#439af1"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_index"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:padding="6dp"
        android:textSize="25sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:padding="5dp"
        android:textSize="28sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="start"
        android:padding="10dp"
        android:textSize="22sp" />

</LinearLayout>
複製代碼

以後就是繼承 CommonRecyclerViewAdapter ，泛型指定爲 New ，在構造函數裏直接指定要使用的佈局爲 R.layout.item_new，再實現幾個抽象方法便可。

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:55
 * 說明：單個佈局
 */
public class NewCommonAdapter extends CommonRecyclerViewAdapter<New> {

    public NewCommonAdapter(Context context, List<New> dataList) {
        super(context, dataList, R.layout.item_new);
    }

    @Override
    protected New clone(New data) {
        return new New(data.getIndex(), data.getTitle(), data.getContent());
    }

    @Override
    protected boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
        return dataList.get(oldItemPosition).getIndex() == newDataList.get(newItemPosition).getIndex();
    }

    @Override
    protected boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        String title = dataList.get(oldItemPosition).getTitle();
        String content = dataList.get(oldItemPosition).getContent();
        String newTitle = newDataList.get(newItemPosition).getTitle();
        String newContent = newDataList.get(newItemPosition).getContent();
        return title.equals(newTitle) && content.equals(newContent);
    }

    @NonNull
    @Override
    protected Bundle getChangePayload(int oldItemPosition, int newItemPosition) {
        Bundle bundle = new Bundle();
        String title = dataList.get(oldItemPosition).getTitle();
        String content = dataList.get(oldItemPosition).getContent();
        String newTitle = newDataList.get(newItemPosition).getTitle();
        String newContent = newDataList.get(newItemPosition).getContent();
        if (!title.equals(newTitle)) {
            bundle.putString("Title", newTitle);
        }
        if (!content.equals(newContent)) {
            bundle.putString("Content", newContent);
        }
        return bundle;
    }

    @Override
    protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
        for (String key : bundle.keySet()) {
            switch (key) {
                case "Title":
                    holder.setText(R.id.tv_title, bundle.getString(key));
                    break;
                case "Content":
                    holder.setText(R.id.tv_content, bundle.getString(key));
                    break;
            }
        }
    }

    @Override
    protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
        holder.setText(R.id.tv_title, data.getTitle())
                .setText(R.id.tv_content, data.getContent());
    }

}
複製代碼

這裏省略 Activity 中對 RecyclerView 的各類初始化操做，只展示最終效果，具體代碼看最下方GitHub地址。 效果圖以下所示：

3、通用的多佈局 RecyclerView.Adapter 使用示例

在 CommonRecyclerViewAdapter 類當中，爲了支持多佈局，經過 MultiTypeSupport 接口來返回相應的佈局文件ID，這裏除了使用 單佈局 中使用的 R.layout.item_new 佈局文件外，同時使用另一個佈局文件 R.layout.item_new_multi ，僅僅是背景色不一樣而已

想要讓子 Adapter 支持多佈局，只要實現 CommonRecyclerViewAdapter 的另一個構造函數便可。這裏在索引爲單數時使用 R.layout.item_new 佈局，雙數時使用 R.layout.item_new_multi 佈局

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:56
 * 說明：多佈局
 */
public class NewCommonMultiAdapter extends CommonRecyclerViewAdapter<New> {

    public NewCommonMultiAdapter(Context context, List<New> dataList) {
        super(context, dataList, new CommonRecyclerViewAdapter.MultiTypeSupport<New>() {
            @Override
            public int getLayoutId(New item, int position) {
                return item.getIndex() % 2 == 0 ? R.layout.item_new_multi : R.layout.item_new;
            }
        });
    }
	
	//省略一些代碼
    ......

    @Override
    protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
        if (bundle.size() > 0) {
            int index = bundle.getInt("Index");
            for (String key : bundle.keySet()) {
                switch (key) {
                    case "Title":
                        if (index % 2 == 0) {
                            holder.setText(R.id.tv_multi_title, bundle.getString(key));
                        } else {
                            holder.setText(R.id.tv_title, bundle.getString(key));
                        }
                        break;
                    case "Content":
                        if (index % 2 == 0) {
                            holder.setText(R.id.tv_multi_content, bundle.getString(key));
                        } else {
                            holder.setText(R.id.tv_content, bundle.getString(key));
                        }
                        break;
                }
            }
        }
    }

    @Override
    protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
        if (data.getIndex() % 2 == 0) {
            holder.setText(R.id.tv_multi_title, data.getTitle())
                    .setText(R.id.tv_multi_content, data.getContent())
                    .setText(R.id.tv_multi_index, String.valueOf(data.getIndex()));
        } else {
            holder.setText(R.id.tv_title, data.getTitle())
                    .setText(R.id.tv_content, data.getContent())
                    .setText(R.id.tv_index, String.valueOf(data.getIndex()));
        }
    }

}
複製代碼

實現的最終效果以下所示：

4、帶頭部與底部View的 RecyclerView

爲了實現帶頭部與底部View的 RecyclerView ，須要自定義一個Adapter來包裹實際的Adapter，重寫 getItemViewType(int position) 方法，返回不一樣的值以區分頭部View與底部View，並向外開放添加和移除頭部底部View的方法

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:53
 * 說明：可添加頭部View與底部View的RecyclerView Adapter
 */
public class WrapRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private RecyclerView.Adapter<RecyclerView.ViewHolder> innerAdapter;

    private SparseArray<View> headerViewArray;

    private SparseArray<View> footerViewArray;

    //頭部View類型開始位置,用於viewType
    private static int BASE_VIEW_TYPE_HEADER = 1000;

    //底部View類型開始位置,用於viewType
    private static int BASE_VIEW_TYPE_FOOTER = 2000;

    private RecyclerView.AdapterDataObserver dataObserver = new RecyclerView.AdapterDataObserver() {

        @Override
        public void onChanged() {
            super.onChanged();
            notifyDataSetChanged();
        }

        @Override
        public void onItemRangeChanged(int positionStart, int itemCount) {
            super.onItemRangeChanged(positionStart, itemCount);
            notifyItemRangeChanged(positionStart + getHeaderViewCount(), itemCount);
        }

        @Override
        public void onItemRangeInserted(int positionStart, int itemCount) {
            super.onItemRangeInserted(positionStart, itemCount);
            notifyItemRangeInserted(positionStart + getHeaderViewCount(), itemCount);
        }

        @Override
        public void onItemRangeRemoved(int positionStart, int itemCount) {
            super.onItemRangeRemoved(positionStart, itemCount);
            notifyItemRangeRemoved(positionStart + getHeaderViewCount(), itemCount);
        }

        @Override
        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            super.onItemRangeMoved(fromPosition, toPosition, itemCount);
            int headerViewsCountCount = getHeaderViewCount();
            notifyItemRangeChanged(fromPosition + headerViewsCountCount, toPosition + headerViewsCountCount + itemCount);
        }
    };

    public WrapRecyclerViewAdapter(RecyclerView.Adapter innerAdapter) {
        headerViewArray = new SparseArray<>();
        footerViewArray = new SparseArray<>();
        setAdapter(innerAdapter);
    }

    private void setAdapter(RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
        innerAdapter = adapter;
        innerAdapter.registerAdapterDataObserver(dataObserver);
    }

    @Override
    public int getItemViewType(int position) {
        if (isHeaderPosition(position)) {
            return headerViewArray.keyAt(position);
        }
        if (isFooterPosition(position)) {
            return footerViewArray.keyAt(position - headerViewArray.size() - getDataItemCount());
        }
        return innerAdapter.getItemViewType(position - headerViewArray.size());
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (isHeaderView(viewType)) {
            return new ViewHolder(headerViewArray.get(viewType));
        }
        if (isFooterView(viewType)) {
            return new ViewHolder(footerViewArray.get(viewType));
        }
        return innerAdapter.onCreateViewHolder(parent, viewType);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        int headerViewsCountCount = getHeaderViewCount();
        if (position >= headerViewsCountCount && position < headerViewsCountCount + innerAdapter.getItemCount()) {
            innerAdapter.onBindViewHolder(holder, position - headerViewsCountCount);
        }
    }

    @Override
    public int getItemCount() {
        return getHeaderViewCount() + getDataItemCount() + getFooterViewCount();
    }

    private int getDataItemCount() {
        return innerAdapter == null ? 0 : innerAdapter.getItemCount();
    }

    public int getHeaderViewCount() {
        return headerViewArray.size();
    }

    public int getFooterViewCount() {
        return footerViewArray.size();
    }

    public RecyclerView.Adapter getInnerAdapter() {
        return innerAdapter;
    }

    /**
     * 判斷是不是頭部View
     *
     * @param viewType ViewType
     * @return 是不是頭部View
     */
    private boolean isHeaderView(int viewType) {
        return headerViewArray.indexOfKey(viewType) > -1;
    }

    /**
     * 判斷是不是底部View
     *
     * @param viewType ViewType
     * @return 是不是底部View
     */
    private boolean isFooterView(int viewType) {
        return footerViewArray.indexOfKey(viewType) > -1;
    }

    /**
     * 判斷是不是頭部View
     *
     * @param view View
     * @return 是不是頭部View
     */
    public boolean isHeaderView(View view) {
        return headerViewArray.indexOfValue(view) > -1;
    }

    /**
     * 判斷是不是底部View
     *
     * @param view View
     * @return 是不是底部View
     */
    public boolean isFooterView(View view) {
        return footerViewArray.indexOfValue(view) > -1;
    }

    /**
     * 根據索引判斷該位置的View是不是頭部View
     *
     * @param position 索引
     * @return 是不是頭部View
     */
    private boolean isHeaderPosition(int position) {
        return position >= 0 && position < getHeaderViewCount();
    }

    /**
     * 根據索引判斷該位置的View是不是底部View
     *
     * @param position 索引
     * @return 是不是底部View
     */
    private boolean isFooterPosition(int position) {
        return position >= (getHeaderViewCount() + getDataItemCount())
                && position < (getHeaderViewCount() + getDataItemCount() + getFooterViewCount());
    }

    /**
     * 添加頭部View
     *
     * @param view 頭部View
     */
    public void addHeaderView(View view) {
        if (headerViewArray.indexOfValue(view) < 0) {
            headerViewArray.put(BASE_VIEW_TYPE_HEADER++, view);
            notifyItemInserted(headerViewArray.size() - 1);
        }
    }

    /**
     * 添加底部View
     *
     * @param view 底部View
     */
    public void addFooterView(View view) {
        if (footerViewArray.indexOfValue(view) < 0) {
            footerViewArray.put(BASE_VIEW_TYPE_FOOTER++, view);
            notifyItemInserted(getHeaderViewCount() + getDataItemCount() + getFooterViewCount() - 1);
        }
    }

    /**
     * 移除頭部View
     *
     * @param view View
     */
    public void removeHeaderView(View view) {
        int index = headerViewArray.indexOfValue(view);
        if (index > -1) {
            headerViewArray.removeAt(index);
            notifyItemRemoved(index);
        }
    }

    /**
     * 移除底部View
     *
     * @param view View
     */
    public void removeFooterView(View view) {
        int index = footerViewArray.indexOfValue(view);
        if (index > -1) {
            footerViewArray.removeAt(index);
            notifyItemRemoved(getHeaderViewCount() + getDataItemCount() + index);
        }
    }

    private class ViewHolder extends RecyclerView.ViewHolder {

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

    }

}
複製代碼

WrapRecyclerViewAdapter 的使用方法也很簡單，只要將實際的Adapter做爲參數來構造 WrapRecyclerViewAdapter 對象，而後再傳給 RecyclerView 便可，以後就能夠經過 addHeaderView 和 addFooterView 方法來添加頭部和底部View

RecyclerView rv_wrapDataList = (RecyclerView) findViewById(R.id.rv_wrapDataList);
        NewCommonAdapter adapter = new NewCommonAdapter(this, newList);
        WrapRecyclerViewAdapter wrapRecyclerViewAdapter = new WrapRecyclerViewAdapter(adapter);
        rv_wrapDataList.setLayoutManager(new LinearLayoutManager(this));
        rv_wrapDataList.setAdapter(wrapRecyclerViewAdapter);
複製代碼

使用效果以下所示：

5、RecyclerView 的單擊和長按事件監聽

RecyclerView 的單擊和長按事件一直是一個比較麻煩的地方，畢竟沒有官方提供的接口，不過此處 CommonRecyclerViewAdapter 也已經提供了相應的設置方法

NewCommonMultiAdapter newCommonMultiAdapter = new NewCommonMultiAdapter(this, newList);
        newCommonMultiAdapter.setClickListener(new CommonRecyclerViewHolder.OnClickListener() {
            @Override
            public void onClick(int position) {
                toast("單擊" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
            }
        });
        newCommonMultiAdapter.setLongClickListener(new CommonRecyclerViewHolder.OnLongClickListener() {
            @Override
            public void onLongClick(int position) {
                toast("長按" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
            }
        });
複製代碼

6、通用的 RecyclerView.ItemDecoration

想要實現Item之間的分割線，須要繼承 RecyclerView.ItemDecoration 在相應的位置進行繪製，這裏提供一個通用的分隔線

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 21:52
 * 說明：通用分隔線
 */
public class CommonItemDecoration extends RecyclerView.ItemDecoration{

    private int orientation = LinearLayoutManager.HORIZONTAL;

    private Drawable drawable;

    public CommonItemDecoration(Context context, int orientation) {
        this.orientation = orientation;
        int[] attrs = new int[]{android.R.attr.listDivider};
        TypedArray typedArray = context.obtainStyledAttributes(attrs);
        drawable = typedArray.getDrawable(0);
        typedArray.recycle();
    }

    public CommonItemDecoration(Drawable drawable, int orientation) {
        this.drawable = drawable;
        this.orientation = orientation;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        if (orientation == LinearLayoutManager.HORIZONTAL) {
            outRect.set(0, 0, drawable.getIntrinsicWidth(), 0);
        } else if (orientation == LinearLayoutManager.VERTICAL) {
            outRect.set(0, 0, 0, drawable.getIntrinsicHeight());
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        if (orientation == LinearLayoutManager.HORIZONTAL) {
            drawVerticalDivider(c, parent);
        } else if (orientation == LinearLayoutManager.VERTICAL) {
            drawHorizontalDivider(c, parent);
        }
    }

    private void drawVerticalDivider(Canvas c, RecyclerView parent) {
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
//            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
//            //受 child layout_marginEnd 屬性的影響
//            int left = child.getRight() + params.rightMargin;
            //不受 child layout_marginEnd 屬性的影響，會直接繪製在 child 右側
            int left = child.getRight();
            int top = child.getTop();
            int right = left + drawable.getIntrinsicWidth();
            int bottom = child.getBottom();
            drawable.setBounds(left, top, right, bottom);
            drawable.draw(c);
        }
    }

    private void drawHorizontalDivider(Canvas c, RecyclerView parent) {
        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            int left = child.getLeft();
            //不受 child layout_marginBottom 屬性的影響，會直接繪製在 child 底部
            int top = child.getBottom();
            int right = child.getRight();
            int bottom = top + drawable.getIntrinsicHeight();
            //會受 child layout_marginBottom 屬性的影響
            //RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            //int top = child.getBottom() + params.bottomMargin;
            drawable.setBounds(left, top, right, bottom);
            drawable.draw(c);
        }
    }

}
複製代碼

在以前的幾張效果圖中，實際上是已經爲RecyclerView添加了一條白色分隔線的，

RecyclerView rv_commonMultiDataList = (RecyclerView) findViewById(R.id.rv_commonMultiDataList);
CommonItemDecoration commonItemDecoration = new CommonItemDecoration(ContextCompat.getDrawable(this, R.drawable.divider), LinearLayoutManager.VERTICAL);
        rv_commonMultiDataList.addItemDecoration(commonItemDecoration);
複製代碼

這裏也能夠傳入不一樣的 Drawable 對象，從而實現多種風格的分隔線

7、SnapHelper的使用

順帶在這裏對 SnapHelper 進行一個簡單的介紹，SnapHelper 是在 Android 24.2.0 的support 包中新添加的一個支持庫，是對RecyclerView的拓展。SnapHelper旨在支持RecyclerView的對齊方式，經過計算對齊RecyclerView中TargetView 的指定點或者容器中的任何像素點，可使RecyclerView實現相似於 ViewPager 的切換效果

SnapHelper是一個抽象類，官方提供了 LinearSnapHelper 和 PagerSnapHelper 兩個具體實現，這裏來實現相似於第一次使用App時顯示的引導頁的效果

/**
 * 做者：葉應是葉
 * 時間：2017/12/21 22:02
 * 說明：
 */
public class SnapRecyclerViewActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_snap_recycler_view);
        RecyclerView rv_snap = (RecyclerView) findViewById(R.id.rv_snap);
        SnapAdapter snapAdapter = new SnapAdapter(this, getData());
        rv_snap.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false));
//        rv_snap.setLayoutManager(new LinearLayoutManager(this));
        rv_snap.setAdapter(snapAdapter);
//        LinearSnapHelper snapHelper = new LinearSnapHelper();
//        snapHelper.attachToRecyclerView(rv_snap);
        PagerSnapHelper pagerSnapHelper=new PagerSnapHelper();
        pagerSnapHelper.attachToRecyclerView(rv_snap);
    }

    private List<Image> getData() {
        List<Image> imageList = new ArrayList<>();
        imageList.add(new Image(0, R.drawable.drawable_1));
        imageList.add(new Image(1, R.drawable.drawable_0));
        imageList.add(new Image(2, R.drawable.drawable_1));
        imageList.add(new Image(3, R.drawable.drawable_0));
        imageList.add(new Image(4, R.drawable.drawable_1));
        imageList.add(new Image(5, R.drawable.drawable_0));
        imageList.add(new Image(6, R.drawable.drawable_1));
        imageList.add(new Image(7, R.drawable.drawable_0));
        return imageList;
    }

}
複製代碼

實現的效果以下所示：

源代碼我也已經放到了GitHub上，點擊查看：Android RecyclerView的簡便寫法