Android 进阶之重要的控件 RecycleView

RecycleView 是2014年Google IO 引入的新的控件，它是以 v7 support libraries的形式存在的，可以用在之前的Android系统版本。它的引入主要是用于增强ListView的功能。与其它的View不一样的地方是RecyclerView不负责子view的展现和布局工作，它关注的是子view的回收与复用。而子view的布局、装饰、动画都交给了其内部类来负责。

ViewHolder ：用来放置每个item所包含子view的容器。在Adapter中负责创建和填充ViewHolder
Adapter ：用于绑定数据和ViewHolder
LayoutManager ：布局管理器，负责子View的位置安排
ItemDecoration ：用来装饰子view
ItemAnimator ：用于添加子View，增加删除的动画

RecycleView的简单使用

下面就由简单到复杂一步一步介绍它的使用。

1.在项目中引入recycleview的依赖关系。

compile 'com.android.support:recyclerview-v7:23.4.0'

如果大家不是很清楚recycleview的版本号的话，可以使用project structrue -> dependencies 输入recycleview，这时候会自动帮你查找对应的版本。

Adapter 负责生成出绑定数据后的ViewHolder，它继承自RecyclerView.Adapter，一般而言它有一个构造方法用于用于传入两个参数，一个是上下文内容，一个是数据列表，还可以有另外一个参数用于传入布局id。

public class MyRecycleViewAdapter extends RecyclerView.Adapter<MyRecycleViewAdapter.ViewHolder> {

    private Context mContext;
    private ArrayList<String> mList;
    MyRecycleViewAdapter(Context context, List<String> list) {
        mContext = context;
        mList = (ArrayList<String>) list;
    }
}

由于它继承自RecyclerView.Adapter所以必须覆写：
onCreateViewHolder
onBindViewHolder
getItemCount

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    LayoutInflater mInflater = LayoutInflater.from(parent.getContext());
    View itemView = mInflater.inflate(R.layout.recycleview_item, parent, false);
    return new ViewHolder(itemView);
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    String content = mList.get(position);
    holder.mContentView.setText(content);
}
@Override
public int getItemCount() {
    return mList.size();
}

onCreateViewHolder 负责使用item layout 初始化出一个ItemView，再将ItemView传入ViewHoder，在ViewHolder中创建出构成ItemView的每个子View然后作为参数传递给onBindViewHolder，onBindViewHolder有两个参数，一个是onCreateViewHolder创建的ViewHolder，另一个是数据对应的位置，可以通过第二个参数重数据源中取出数据，然后和ViewHoder中的控件绑定。

下面是ViewHolder的实现：

public class ViewHolder extends RecyclerView.ViewHolder {
    public TextView mContentView;
    public ViewHolder(View itemView) {
        super(itemView);
        mContentView = (TextView) itemView.findViewById(R.id.listview_item);
    }
}

最后初始化整个RecycleView：

public class MainActivity extends AppCompatActivity {
    private RecyclerView mRecycleView = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRecycleView = (RecyclerView) findViewById(R.id.recycle_view);
        mRecycleView.setLayoutManager(new GridLayoutManager(this,2));
        List<String> stringlist = new ArrayList<>();
        for(int i =0;i<100;i++) {
            stringlist.add("Item " + i);
        }
        mRecycleView.setAdapter(new MyRecycleViewAdapter(this,stringlist));
        mRecycleView.setItemAnimator(new DefaultItemAnimator());
    }
}

RecycleView组成

RecyclerView.LayoutManager
RecyclerView.ItemDecoration
RecyclerView.ItemAnimator
ItemAnimator 用于在往RecycleView中添加删除或者移动Item的时候添加动画。默认情况下使用的是DefaultItemAnimator，在实际项目的时候会需要实现这个部分，如果大家有这种需求可以参考：
https://github.com/wasabeef/recyclerview-animators

多类型Item布局

在RecyclerView.Adopter中要实现多类型Item布局需要覆写如下方法：

public int getItemViewType(int position)

并按照如下方法重新修改Adapter：

public class MyRecycleViewAdapter extends
/*这里改为RecyclerView.ViewHolder 因为这时候需要两个ViewHoder*/
RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private Context mContext;
    private ArrayList<String> mList;
    /*定义一个枚举类型用于指定item的类型*/
    private enum ITEM_TYPE {
        TYPE_ONE,
        TYPE_TWO
    };
    /*根据对应的position返回当前的item类型*/
    @Override
    public int getItemViewType(int position) {
        return (position % 2 == 0) ? ITEM_TYPE.TYPE_ONE.ordinal():ITEM_TYPE.TYPE_TWO.ordinal();
    }

    MyRecycleViewAdapter(Context context, List<String> list) {
        mContext = context;
        mList = (ArrayList<String>) list;
    }

	/*根据对应的viewType创建并返回对应的ViewHolder*/
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater mInflater = LayoutInflater.from(parent.getContext());
        View itemView = null;
        if(viewType == ITEM_TYPE.TYPE_ONE.ordinal()) {
            itemView = mInflater.inflate(R.layout.recycleview_item, parent, false);
            return new ViewHolder(itemView);
        }else{
            itemView = mInflater.inflate(R.layout.recycleview_two, parent, false);
            return new ViewHolderTwo(itemView);
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        String content = mList.get(position);
        if(holder instanceof MyRecycleViewAdapter.ViewHolder) {
            ((ViewHolder) holder).mContentView.setText(content);
        }else if(holder instanceof MyRecycleViewAdapter.ViewHolderTwo) {
            ((ViewHolderTwo) holder).mImageView.setImageResource(R.mipmap.ic_launcher);
            ((ViewHolderTwo) holder).mContentView.setText(content);
        }
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mContentView;
        public ViewHolder(View itemView) {
            super(itemView);
            mContentView = (TextView) itemView.findViewById(R.id.listview_item);
        }
    }
    public class ViewHolderTwo extends RecyclerView.ViewHolder {
        public TextView mContentView;
        private ImageView mImageView;
        public ViewHolderTwo(View itemView) {
            super(itemView);
            mImageView = (ImageView) itemView.findViewById(R.id.imageicon);
            mContentView = (TextView) itemView.findViewById(R.id.itemtext);
        }
    }
}

添加ItemDecoration

首先创建一个新的类继承自RecyclerView.ItemDecoration。
https://gist.github.com/alexfu/0f464fc3742f134ccd1e/

class ItemDecortion 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 ItemDecortion(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 onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        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);
            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);
        }
    }
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

然后在设置adapter之前，使用addItemDecoration()方法添加分割线.

mRecycleView.addItemDecoration(new ItemDecortion(this,ItemDecortion.VERTICAL_LIST));
        mRecycleView.setAdapter(new MyRecycleViewAdapter(this,stringlist));

添加点击事件：

ListView 和RecycleView最大的不同就是没有OnItemClickListener来识别item的点击，我们必须自己通过扩展RecyclerView.OnItemTouchListener类来实现这个功能。

private interface onClickListener {
    public void onClick(View view, int position);
    public void onLongClick(View view,int position);
}

public static class RecyclerTouchListener implements RecyclerView.OnItemTouchListener {
    private GestureDetector gestureDetector;
    private MainActivity.onClickListener clickListener;
    public RecyclerTouchListener(Context context, final RecyclerView recyclerView, final MainActivity.onClickListener clickListener) {
        this.clickListener = clickListener;
        gestureDetector = new GestureDetector(context, new GestureDetector.SimpleOnGestureListener() {
            @Override
            public boolean onSingleTapUp(MotionEvent e) {
                return true;
            }
            public void onLongPress(MotionEvent e) {
                View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
                if (child != null && clickListener != null) {
                    clickListener.onLongClick(child, recyclerView.getChildPosition(child));
                }
            }
        });
    }
    public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
        View child = rv.findChildViewUnder(e.getX(), e.getY());
        if (child != null && clickListener != null && gestureDetector.onTouchEvent(e)) {
            clickListener.onClick(child, rv.getChildPosition(child));
        }
        return false;
    }
    public void onTouchEvent(RecyclerView rv, MotionEvent e) {
    }

    public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {

    }
}

recyclerView.addOnItemTouchListener(new RecyclerTouchListener(getApplicationContext(), recyclerView, new ClickListener() {
    public void onClick(View view, int position) {
        Movie movie = movieList.get(position);
        Toast.makeText(getApplicationContext(), movie.getTitle() + " is selected!", Toast.LENGTH_SHORT).show();
    }
    public void onLongClick(View view, int position) {

    }
}));

增删改Item项

在ListView中每当Adapter数据项改变的时候一般执行notifyDataSetChanged()来通知数据集的改变，但是RecyclerView.Adapter 提供了 notifyItemInserted(), notifyItemChanged() 和 notifyItemRemoved()三个方法来通知数据集的修改。