RecyclerView是Android5.0中出現的新控制元件，官方API解釋就一句話：

A flexible view for providing a limited window into a large data set

整體架構如下圖：

RecyclerView的靈活性體現在6個方面：

• 可以控制顯示方式，包括三個內建的不覺管理器，也可以定製
• LinearLayoutManager 以垂直或水平滾動列表方式顯示專案
• GridLayoutManager 在網格中顯示專案
• StaggeredGridLayoutManager 瀑布了流中顯示專案
• 預設情況下顯示增加刪除的動畫，也擴RecyclerView.ItemAnimator定製
• 預設情況無分割線，可以擴充套件ItemDecoration定製

參考資料

官方Demo效果

官方提供了一個Demo(github地址)的執行效果是這樣的:

程式碼比較簡單，重要的內容包括RecyclerView的初始化和其對應的Adapter的構造。

引申需求

設定分割線

分割線官方並沒有提供預設的型別，預設也並沒有分隔線。要提供分隔線必須自己實現RecyclerView.ItemDecoration。

/**
 * An ItemDecoration allows the application to add a special drawing and layout offset
 * to specific item views from the adapter's data set. This can be useful for drawing dividers
 * between items, highlights, visual grouping boundaries and more.
 *
 * <p>All ItemDecorations are drawn in the order they were added, before the item
 * views (in {@link ItemDecoration#onDraw(Canvas, RecyclerView, RecyclerView.State) onDraw()}
 * and after the items (in {@link ItemDecoration#onDrawOver(Canvas, RecyclerView,
 * RecyclerView.State)}.</p>
 */
 

public static abstract class ItemDecoration {
    /**
     * Draw any appropriate decorations into the Canvas supplied to the RecyclerView.
     * Any content drawn by this method will be drawn before the item views are drawn,
     * and will thus appear underneath the views.
     *
     * @param c Canvas to draw into
     * @param
 
 parent RecyclerView this ItemDecoration is drawing into
     * @param state The current state of RecyclerView
     */
    public void onDraw(Canvas c, RecyclerView parent, State state) {
        onDraw(c, parent);
    }

    /**
     * @deprecated
     * Override {@link #onDraw(Canvas, RecyclerView, RecyclerView.State)}
     */
    @Deprecated
    public void onDraw(Canvas c, RecyclerView parent) {
    }

    /**
     * Draw any appropriate decorations into the Canvas supplied to the RecyclerView.
     * Any content drawn by this method will be drawn after the item views are drawn
     * and will thus appear over the views.
     *
     * @param c Canvas to draw into
     * @param parent RecyclerView this ItemDecoration is drawing into
     * @param state The current state of RecyclerView.
     */
    public void onDrawOver(Canvas c, RecyclerView parent, State state) {
        onDrawOver(c, parent);
    }

    /**
     * @deprecated
     * Override {@link #onDrawOver(Canvas, RecyclerView, RecyclerView.State)}
     */
    @Deprecated
    public void onDrawOver(Canvas c, RecyclerView parent) {
    }


    /**
     * @deprecated
     * Use {@link #getItemOffsets(Rect, View, RecyclerView, State)}
     */
    @Deprecated
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        outRect.set(0, 0, 0, 0);
    }

    /**
     * Retrieve any offsets for the given item. Each field of <code>outRect</code> specifies
     * the number of pixels that the item view should be inset by, similar to padding or margin.
     * The default implementation sets the bounds of outRect to 0 and returns.
     *
     * <p>
     * If this ItemDecoration does not affect the positioning of item views, it should set
     * all four fields of <code>outRect</code> (left, top, right, bottom) to zero
     * before returning.
     *
     * <p>
     * If you need to access Adapter for additional data, you can call
     * {@link RecyclerView#getChildAdapterPosition(View)} to get the adapter position of the
     * View.
     *
     * @param outRect Rect to receive the output.
     * @param view    The child view to decorate
     * @param parent  RecyclerView this ItemDecoration is decorating
     * @param state   The current state of RecyclerView.
     */
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
        getItemOffsets(outRect, ((LayoutParams) view.getLayoutParams()).getViewLayoutPosition(),
                parent);
    }
}

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * 參考：https://android.googlesource.com/platform/development/+/master/samples/Support7Demos/src
 * /com/example/android/supportv7/widget/decorator/DividerItemDecoration.java#101
 */
public class DividerItemDecoration extends RecyclerView.ItemDecoration {

    private static final int[] ATTRS = new int[]{
            android.R.attr.listDivider
    };

    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;

    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    private Drawable mDivider;

    private int mOrientation;

    public DividerItemDecoration(Context context, int orientation) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
        setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
            throw new IllegalArgumentException("invalid orientation");
        }
        mOrientation = orientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent) {

        if (mOrientation == VERTICAL_LIST) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }

    }


    public void drawVertical(Canvas c, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getWidth() - parent.getPaddingRight();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            android.support.v7.widget.RecyclerView v = new android.support.v7.widget.RecyclerView(parent.getContext());
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getHeight() - parent.getPaddingBottom();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
    /**
     * outRect是用來設定left、top、right、bottom的padding值的
     * */
    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

點選事件

RecyclerView本身不提供單擊和長按事件，需要自己實現。分為幾個步驟。
第一步，需要在CustomAdapter中自己定義回撥介面。

    /**
     * 點選事件介面
     * */
    public interface OnItemClickListener{
        void onItemClick(View view,int position);
        void onItemLongClick(View view,int position);
    }
    private OnItemClickListener onItemClickListener;

    public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
        this.onItemClickListener = onItemClickListener;
    }

第二步，在CustomAdapter中的onBindViewHolder(ViewHolder viewHolder, final int position)中呼叫介面函式。

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, final int position) {
        Log.d(TAG, "Element " + position + " set.");

        // Get element from your dataset at this position and replace the contents of the view
        // with that element
        viewHolder.getTextView().setText(mDataSet[position]);
        viewHolder.setColor(position);
        if (onItemClickListener!=null){
            //可以獲得每個item的包裝類itemView
            viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    onItemClickListener.onItemClick(v,position);
                }
            });
            viewHolder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    onItemClickListener.onItemLongClick(v,position);
                    return true;
                }
            });
        }
    }

第三步，在CustomAdapter初始化的地方傳入該介面例項。

 mAdapter.setOnItemClickListener(new CustomAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
               ××××單擊事件××××××
            }

            @Override
            public void onItemLongClick(View view, int position) {
              ××××長按事件××××××
            }
        });

多選模式

多選模式可以採用ActionMode來進行UI設計，本質上是通過長按進入ActionMode模式，可以點選按鈕取消多選模式。
這裡配合上面的點選事件，僅僅模擬了多選的操作，而沒有新增ActionMode。

mAdapter.setOnItemClickListener(new CustomAdapter.OnItemClickListener() {
    @Override
    public void onItemClick(View view, int position) {
        if (isOnLonCliked){
            addOrRemove(position);
            Log.i(TAG, position+"OnLonCliked");
        }else {
            Toast.makeText(getActivity(),position+" clicked",Toast.LENGTH_LONG).show();
        }
    }
    @Override
    public void onItemLongClick(View view, int position) {
        isOnLonCliked=true;
        Log.i(TAG, position+"OnLonCliked");
    }
});

其中，addOrRemove(int position)多選的邏輯。

**
 * 模擬多選情況
 * */
private void  addOrRemove(int position){
    if(mAdapter.positionSet.contains(position)){
        mAdapter.positionSet.remove(position);
    }else {
        mAdapter.positionSet.add(position);
    }
    if (mAdapter.positionSet.size()==0){
        isOnLonCliked=false;
    }
    mAdapter.notifyDataSetChanged();
}

CustomAdapter中有一個集合在記錄多選模式下已經點選的位置，點選時判斷該集合是否包含了該位置，如果已經包含，就取消顏色，否則改變顏色。

/**
 * Provide views to RecyclerView with data from mDataSet.
 */

     ××××××省略無關程式碼××××××××××××××

    public static Set<Integer> positionSet = new HashSet<>();

    // BEGIN_INCLUDE(recyclerViewSampleViewHolder)
    /**
     * Provide a reference to the type of views that you are using (custom ViewHolder)
     */
    public static class ViewHolder extends RecyclerView.ViewHolder {
        public final TextView textView;

        public ViewHolder(View v) {
            super(v);
            // Define click listener for the ViewHolder's View.
            v.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Log.d(TAG, "Element " + getAdapterPosition() + " clicked.");
                }
            });
            textView = (TextView) v.findViewById(R.id.textView);
            Log.d(TAG, "ViewHolder ");
        }

        public TextView getTextView() {
            return textView;
        }
        public void setColor(int position){
            if (positionSet.contains(position)){
                textView.setTextColor(Color.GREEN);
            }else {
                textView.setTextColor(Color.BLACK);
            }

        }
    }
××××××省略無關程式碼××××××××××××××

最後達成的效果是

• 長按RecyclerView中的某一項，會進入到多選模式

• 如果點選的項已經在CustomAdapter中的集合中，則去除這些項，如果集合清空，則退出多選模式

• 多選模式下再點選某些項，這些項會記錄到CustomAdapter中的集合中
  

GitHub地址