Android之RecyclerView的使用总结

小鱼儿 2022-09-22 01:13 115阅读 0赞

### 1.RecycleView的简介 ###

可以简单理解RecyclerView就是ListView，是一个更高级的ListView。

### 2.RecyclerView的特点 ###

*  不关心Item显示在正确的位置，以及如何显示。
 *  不关心Item之间如何分割。
 *  不关注Item的添加和删除的效果。
 *  仅仅关注如何回收与复用View。

### 3.在项目中如何引用 ###

在模块的gradle.build文件中添加如下依赖

dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
        compile 'com.android.support:recyclerview-v7:22.0.0'
    
    }

### 4.RecyclerView中关键点说明 ###

#### 1.Adapter ####

这个Adapter比较特殊，是RecyclerView所特有的，它包括以下几个重要的方法：

public abstract VH onCreateViewHolder(ViewGroup parent, int viewType);
    public abstract void onBindViewHolder(ViewHolder holder, int position);
    public abstract int getItemCount();

onCreateViewHolder：用于创建ViewHolder，或者是根据viewType创建ViewHolder。  
onBindViewHolder：通过ViewHolder和数据绑定。  
getItemCount：获得Item的数量。

#### 2.ViewHolder ####

一个抽象类，通过继承此类对View进行封装。

#### 3.LayoutManager ####

布局管理器，用于管理RecyclerView中数据的显示方式。目前主要有三种布局管理器，分别是：

*  LinearLayoutManager
 *  GridLayoutManager
 *  StaggeredGridLayoutManager

LinearLayoutManager：线性布局管理器，通过使用这个布局就可以实现ListView的效果。可以实现垂直、水平两种方向的ListView效果，默认的是垂直方向的ListView效果。

GridLayoutManager：网格布局管理器,通过使用这个布局管理器可以实现GridView的效果，同样的，它也用垂直和水平两种显示方式。

StaggeredGridLayoutManager：交错网格布局管理器，可以实现具有瀑布流效果的显示，它也是有垂直和水平两种显示方式的。

### 5.实例讲解 ###

#### 1.使用LinearLayoutManager实现垂直显示的效果 ####

main\_activity.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.gjg.learn.recycleviewdemo.MainActivity">
    
    
        <android.support.v7.widget.RecyclerView android:id="@+id/id_recyclerview" android:layout_width="match_parent" android:layout_height="match_parent" >
    
        </android.support.v7.widget.RecyclerView>
    
    </RelativeLayout>

MainActivity

public class MainActivity extends AppCompatActivity { 
        private RecyclerView recyclerView;
        private List<String> mDatas;
        private RecyclerAdapter recyclerAdapter;
    
    
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            initData();
            recyclerView= (RecyclerView) this.findViewById(R.id.id_recyclerview);
            LinearLayoutManager linearLayoutManager=new LinearLayoutManager(this);
    
            recyclerView.setLayoutManager(linearLayoutManager);
    
            recyclerAdapter=new RecyclerAdapter(mDatas,this);
    
            recyclerView.setAdapter(recyclerAdapter);
            //线性布局的分割线
            DividerItemDecoration decoration=new DividerItemDecoration(this,DividerItemDecoration.HORIZONTAL_LIST);
    
            recyclerView.addItemDecoration(decoration);
            // 设置item动画
            recyclerView.setItemAnimator(new DefaultItemAnimator());
            initEvent();
        }
    
        private void initEvent() {
            recyclerAdapter.setOnItemClickLitener(new RecyclerAdapter.OnItemClickLitener() {
                @Override
                public void onItemClick(View view, int position) {
                    Toast.makeText(MainActivity.this, "你点击了"+mDatas.get(position),
                            Toast.LENGTH_SHORT).show();
                }
    
                @Override
                public void onItemLongClick(View view, int position) {
                    Toast.makeText(MainActivity.this, "你长按了"+mDatas.get(position),
                            Toast.LENGTH_SHORT).show();
                }
            });
        }
    
        private void initData() {
            mDatas = new ArrayList<String>();
            for (int i = 'A'; i < 'z'; i++)
            {
                mDatas.add("字母：" + (char) i);
            }
    
        }
    }

RecyclerAdapter

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.MyViewHolder> { 
        private Context context;
        private List<String> mDatas;
    
        public RecyclerAdapter(List<String> mDatas,Context context){
            this.mDatas=mDatas;
            this.context=context;
    
        }
    
        public interface OnItemClickLitener { 
            void onItemClick(View view, int position);
            void onItemLongClick(View view, int position);
        }
    
        private OnItemClickLitener mOnItemClickLitener;
    
        public void setOnItemClickLitener(OnItemClickLitener mOnItemClickLitener) {
            this.mOnItemClickLitener = mOnItemClickLitener;
        }
    
    
        @Override
        public MyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
    
            //需要把viewGroup加进去，否则item永远居左显示
            View view = LayoutInflater.from(context).inflate(R.layout.recyclerview_item, viewGroup, false);
            MyViewHolder holder = new MyViewHolder(view);
            return holder;
        }
    
        @Override
        public void onBindViewHolder(MyViewHolder myViewHolder, int i) {
            myViewHolder.tv.setText(mDatas.get(i));
            // 如果设置了回调，则设置点击事件
            if (mOnItemClickLitener != null)
            {
                //itemView:ViewHolder的一个item
                myViewHolder.itemView.setOnClickListener(new View.OnClickListener()
                {
                    @Override
                    public void onClick(View v)
                    {
                        int pos = myViewHolder.getLayoutPosition();
    
                        mOnItemClickLitener.onItemClick(myViewHolder.itemView, pos);
    
                    }
                });
    
                myViewHolder.itemView.setOnLongClickListener(new View.OnLongClickListener()
                {
                    @Override
                    public boolean onLongClick(View v)
                    {
                        int pos = myViewHolder.getLayoutPosition();
    
                        mOnItemClickLitener.onItemLongClick(myViewHolder.itemView, pos);
    
                        return false;
                    }
                });
            }
        }
    
        @Override
        public int getItemCount() {
            return mDatas.size();
        }
    
    
        class MyViewHolder extends RecyclerView.ViewHolder { 
            TextView tv;
    
            public MyViewHolder(View itemView) {
                super(itemView);
                tv = (TextView) itemView.findViewById(R.id.id_num);
            }
        }
    }

DividerItemDecoration

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)
        {
            Log.v("itemdecoration", "onDraw()");
             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);
                RecyclerView v = new 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);
            }
        }
    
        @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);
            }
        }
    }

分割线的样式：

divider\_bg

<?xml version="1.0" encoding="utf-8"?>
    <shape xmlns:android="http://schemas.android.com/apk/res/android">
    
        <gradient android:angle="180" android:startColor="#95c247" android:centerColor="#ff099494" android:endColor="#ea74d3" android:type="linear"/>
        <size android:height="2dp"/>
    </shape>

运行效果如下：  
![这里写图片描述][20160624162359769]

注意：在**View view = LayoutInflater.from(context).inflate(R.layout.recyclerview\_item, viewGroup, false);**时，需要把viewGroup加进去，否则item永远居左显示。  
因为：

inflater在inflate一个xml时，需要知道parent的类型，才能生成对应的LayoutParams，才可以把xml根节点的attrs（如layout_width）读进去，代码如下：
                 // android.view.LayoutInflater
                public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
                    synchronized (mConstructorArgs) {
    
                        ...
    
                        // Temp is the root view that was found in the xml
                        final View temp = createViewFromTag(root, name, inflaterContext, attrs);
    
                        ViewGroup.LayoutParams params = null;
    
                        if (root != null) {
                            if (DEBUG) {
                                System.out.println("Creating params from root: " +
                                        root);
                            }
                            // Create layout params that match root, if supplied
                            params = root.generateLayoutParams(attrs);
                            if (!attachToRoot) {
                                // Set the layout params for temp if we are not
                                // attaching. (If we are, we use addView, below)
                                temp.setLayoutParams(params);
                            }
                        }
    
                        ...
    
                    }
                    如果parent传进去为null，生成的View的LayoutParams为null，在RecyclerView.addView时，发现LayoutParams为null，则生成默认的LayoutParams,
    
                    // android.view.ViewGroup
                    protected LayoutParams generateDefaultLayoutParams() {
                        return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
                    }

--------------------

#### 2.使用LinearLayoutManager实现水平显示的效果 ####

只要在MainActivity的onCreateView中添加：  
linearLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);  
修改  
DividerItemDecoration decoration = new DividerItemDecoration(this, DividerItemDecoration.HORIZONTAL\_LIST);  
效果如下：  
![这里写图片描述][20160624165025822]

#### 3.使用GridLayoutManager实现垂直显示的效果 ####

将recyclerView.setLayoutManager(linearLayoutManager);  
改为recyclerView.setLayoutManager(new GridLayoutManager(this,5));  
并且修改分割线的样式：  
DividerGridItemDecoration decoration=new DividerGridItemDecoration(this);  
即可。  
效果如下：  
![这里写图片描述][20160624170821066]

#### 4.使用StaggeredGridLayoutManager实现垂直显示的效果 ####

修改成  
recyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,  
StaggeredGridLayoutManager.VERTICAL));  
还有就是，关键是在onBindViewHolder中设置item的高度，高度为随机生成的。  
LayoutParams lp = holder.tv.getLayoutParams();  
lp.height = mHeights.get(position);  
holder.tv.setLayoutParams(lp);  
效果如图：  
![这里写图片描述][20160624183302293]

[20160624162359769]: /images/20220721/91933e78ccc14b7f9204863e500064bd.png
[20160624165025822]: /images/20220721/1e171be0aabb4c939eea8445563ceaf5.png
[20160624170821066]: /images/20220721/034f31d124ed4cf9982141111d8e63fe.png
[20160624183302293]: /images/20220721/d070ec3318344aa0b46f25b305336968.png