Android——RecyclerView入门学习之RecyclerView.Adapter(三)

梦里梦外; 2023-03-01 06:15 45阅读 0赞

#  #

前使用`RecyclerView.Adapter`，基本就类似套用公式，死步骤，对`Adapter`感到既熟悉又陌生。从去年我开始接触学习`Android`之时，`RecyclerView`已经开始大量被运用，逐步取代`ListView`。遂，正好，那就先直接学习`RecyclerView.Adapter`相关知识

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

# 1. RecyclerView.Adapter适配器 #

`RecyclerView.Adapter`，一个抽象类，并支持泛型

public static abstract class Adapter<VH extends ViewHolder> {
       ...
    }

定义一个`MyRecyclerViewAdapter`继承`RecyclerView.Adapter`后，`Android Stuido`提醒需要重写3个方法，在重写`3`个方法前，一般会先定义一个`Holder`继承`RecycelrView.ViewHolder`，之后直接在`MyRecyclerViewAdapter`上，指定泛型就是`RecyclerHolder`

**3个需要必须重写的方法：**

方法1：public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
    
    方法2：public void onBindViewHolder(RecyclerView.ViewHolder holder, int position)
    
    方法3：public int getItemCount()

在指定了泛型为`RecyclerHoler`后，`方法2`也会根据泛型改变`onBindViewHolder(RecyclerHolder holder, int position)`

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

## 1.1 onCreateViewHolder(ViewGroup parent, int viewType)创建Holder ##

**源码：**

/**
     * Called when RecyclerView needs a new {@link ViewHolder} of the given type to represent an item.
     * 
     * @param parent The ViewGroup into which the new View will be added after it is bound to an adapter position.
     * @param viewType The view type of the new View.
     *
     * @return A new ViewHolder that holds a View of the given view type.
     */
    public abstract VH onCreateViewHolder(ViewGroup parent, int viewType);

*  **ViewGroup parent**：可以简单理解为`item`的根`ViewGroup`，`item`的子控件加载在其中
 *  **int viewType**：`item`的类型，可以根据`viewType`来创建不同的`ViewHolder`，来加载不同的类型的`item`

这个方法就是用来创建出一个新的`ViewHolder`，可以根据需求的`itemType`，创建出多个`ViewHolder`。创建多个`itemType`时，需要`getItemViewType(int position)`方法配合

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

## 1.2 onBindViewHolder(RecyclerHolder holder, int position)绑定ViewHolder ##

**源码:**

**
    *Called by RecyclerView to display the data at the specified position.
    *This method should update the contents of the {@link ViewHolder#itemView} to reflect the item at the given position.
    * 
    *@param holder The ViewHolder which should be updated to represent the contents of the item at the given position in the data set.
    *@param position The position of the item within the adapter's data set.
    */
    
    public abstract void onBindViewHolder(VH holder, int position);

*  **VH holder**：就是在`onCreateViewHolder()`方法中，创建的`ViewHolder`
 *  **int position**：`item`对应的`DataList`数据源集合的`postion`

`postion`就是`adapter position`，`RecycelrView`中`item`的数量，就是根据`DataList`数据源集合的数量来创建的

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

## 1.3 getItemCount()获取Item的数目 ##

**源码：**

/**
     * Returns the total number of items in the data set held by the adapter.
     *
     * @return The total number of items in this adapter.
     */
    public abstract int getItemCount();

这个方法的返回值，便是`RecyclerView`中实际`item`的数量。有些情况下，当增加了`HeaderView`或者`FooterView`后，需要注意考虑这个返回值

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

## 1.4 简单shi yong ##

**一个最简单的RecyclerViewAdapter**

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.RecyclerHolder> {
        private Context mContext;
        private List<String> dataList = new ArrayList<>();
    
        public MyRecyclerViewAdapter(RecyclerView recyclerView) {
            this.mContext = recyclerView.getContext();
        }
    
        public void setData(List<String> dataList) {
            if (null != dataList) {
                this.dataList.clear();
                this.dataList.addAll(dataList);
                notifyDataSetChanged();
            }
        }
    
        @Override
        public RecyclerHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.id_rv_item_layout, parent, false);
            return new RecyclerHolder(view);
        }
    
        @Override
        public void onBindViewHolder(RecyclerHolder holder, int position) {
            holder.textView.setText(dataList.get(position));
        }
    
        @Override
        public int getItemCount() {
            return dataList.size();
        }
    
        class RecyclerHolder extends RecyclerView.ViewHolder {
            TextView textView;
    
            private RecyclerHolder(View itemView) {
                super(itemView);
                textView = (TextView) itemView.findViewById(R.id.tv__id_item_layout);
            }
        }
    }

我的个人习惯是单独使用一个`setData()`方法将`DataList`传递进`Adapter`，看到网上有一些博客中会通过构造方法传递。我一般会在网络请求前就初始化`Adapter`，当异步网络请求拿到解析过的`JSON`数据后，调用这个方法将数据加载进`Adapter`，即使做了分页，也可以比较方。但感觉这种方法终究会浪费一点性能

**注意，在 onCreateViewHolder()方法中：**

View view = LayoutInflater.from(mContext).inflate(R.layout.id_rv_item_layout, parent, false);

`inflate()`方法使用的是3个参数的方法。

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

### 1.4.1 问题 ###

以前使用2个参数的方法`inflate(@LayoutRes int resource, @Nullable ViewGroup root)`，下面的形式

View view = LayoutInflater.from(mContext).inflate(R.layout.id_rv_item_layout,null);

遇到的一个问题

![format_png][]

2个参数方法遇到的问题

两种方法，使用的是同一套布局

`item`内的`TextView`的宽是`match_parent`，但使用两个参数的方法时，看起来却是`wrap_content`的效果

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

### 1.4.2尝试从源码中找问题 ###

**两个参数的方法源码**

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
            return inflate(resource, root, root != null);
    }

两个参数的方法内部调用了3个参数的方法，此时`inflate(resourceId, null, false)`，`root`为`null`，`attachToRoot`为`false`

最终来到了这里，只保留了部分代码：

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
        ...
        
        View result = root;
        
        ...
        
        // 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) {
        
            ...
            
            params = root.generateLayoutParams(attrs);
            
            ...               
        }
        
        ...
        
        rInflateChildren(parser, temp, attrs, true);
        
        ...
        
        if (root == null || !attachToRoot) {
            result = temp;
        }
     }

使用两个参数的`inflate()`方法，`ViewGroup.LayoutParams params`最终为`null`；而如果使用3个参数的方法，最终`params = params = root.generateLayoutParams(attrs)`

这里为了减少出现问题的出现，就使用3个参数的方法`inflate(R.layout.id_rv_item_layout, parent, false)`

> 这里看源码也就看了这小段一段，inflate()方法的完整过程还是比较复杂的，比较浅显的知道问题出在哪里后，没有深挖

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

## 1.4 点击事件 ##

**完整代码：**

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.RecyclerHolder> {
        private Context mContext;
        private List<String> dataList = new ArrayList<>();
        private onRecyclerItemClickerListener mListener;
    
        public MyRecyclerViewAdapter(RecyclerView recyclerView) {
            this.mContext = recyclerView.getContext();
        }
    
    
        /**
         * 增加点击监听
         */
        public void setItemListener(onRecyclerItemClickerListener mListener) {
            this.mListener = mListener;
        }
    
        /**
         * 设置数据源
         */
        public void setData(List<String> dataList) {
            if (null != dataList) {
                this.dataList.clear();
                this.dataList.addAll(dataList);
                notifyDataSetChanged();
            }
        }
    
        public List<String> getDataList() {
            return dataList;
        }
    
        @Override
        public RecyclerHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.id_rv_item_layout, parent, false);
            // View view = LayoutInflater.from(mContext).inflate(R.layout.id_rv_item_layout,null);
            return new RecyclerHolder(view);
        }
    
        @Override
        public void onBindViewHolder(RecyclerHolder holder, int position) {
            holder.textView.setText(dataList.get(position));
            holder.textView.setOnClickListener(getOnClickListener(position));
        }
    
        private View.OnClickListener getOnClickListener(final int position) {
            return new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (null != mListener && null != v) {
                        mListener.onRecyclerItemClick(v, dataList.get(position), position);
                    }
                }
            };
        }
    
    
        @Override
        public int getItemCount() {
            return dataList.size();
        }
    
        class RecyclerHolder extends RecyclerView.ViewHolder {
            TextView textView;
    
            private RecyclerHolder(View itemView) {
                super(itemView);
                textView = (TextView) itemView.findViewById(R.id.tv__id_item_layout);
            }
        }
    
        /**
         * 点击监听回调接口
         */
        public interface onRecyclerItemClickerListener {
            void onRecyclerItemClick(View view, Object data, int position);
        }
    }

定义一个接口`onRecyclerItemClickerListener`，这样可以在`Actiivty`设置监听对象，之后为`TextView`设置点击监听事件，在`TextView`的点击事件方法中，使用`onRecyclerItemClick()`进行回调

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

**在Activity中使用：**

//设置点击事件
    adapter.setItemListener(new MyRecyclerViewAdapter.onRecyclerItemClickerListener() {
        @Override
        public void onRecyclerItemClick(View view, Object data, int position) {
            String s = (String) data;
            adapter.getDataList().set(position, s + "---->hi");
                adapter.notifyItemChanged(position);
            }
    });

在监控对象回调方法中，使用了`notifyItemChanged(position)`来进行局部刷新

![aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8yMDg2NjgyLTQyMGFiODBmZTVkZjU4NjcuZ2lm][]

点击进行局部刷新

但这种方式会`new`出一大堆`View.OnClickListener`，还有一种思路是利用`RecycelrView`的`onTouchListener`和`GestureDetector`手势来进行设置，可以看看[三种方式实现RecyclerView的Item点击事件][RecyclerView_Item]

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

## 1.5 一系列的notifyData方法 ##

一共有10个方法

<table> 
 <thead> 
  <tr> 
   <th>方法</th> 
   <th>作用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><code>notifyDataSetChanged()</code></td> 
   <td>通知<code>RecycelrView</code>进行全局刷新</td> 
  </tr> 
  <tr> 
   <td><code>notifyItemChanged(int position)</code></td> 
   <td>通知<code>RecycelrView</code>在<code>adapter position</code>处局进行部刷新</td> 
  </tr> 
  <tr> 
   <td><code>notifyItemRemoved(int position)</code></td> 
   <td>通知<code>RecyclerView</code>移除在<code>adapter position</code>处的item</td> 
  </tr> 
  <tr> 
   <td><code>notifyItemMoved(int fromPosition, int toPosition)</code></td> 
   <td>通知<code>RecyclerView</code>移除从<code>fromPosition</code>到<code>toPosition</code>的<code>item</code></td> 
  </tr> 
  <tr> 
   <td><code>notifyItemRangeRemoved(int positionStart, int itemCount)</code></td> 
   <td>通知<code>RecyclerView</code>移除从<code>positionStart</code>开始的<code>itemCount</code>个<code>item</code></td> 
  </tr> 
  <tr> 
   <td><code>notifyItemChanged(int position, Object payload)</code></td> 
   <td>通知<code>RecyclerView</code>改变指定<code>position</code>的<code>item</code>的<code>object</code></td> 
  </tr> 
  <tr> 
   <td><code>notifyItemRangeChanged(int positionStart,int itemCount)</code></td> 
   <td>通知<code>RecyclerView</code>从<code>positionStart</code>开始改变<code>itemCount</code>个<code>item</code></td> 
  </tr> 
  <tr> 
   <td><code>notifyItemRangeChanged(int positionStart,int itemCount,Object payload)</code></td> 
   <td>通知<code>RecyclerView</code>从<code>positionStart</code>开始改变<code>itemCount</code>个<code>item</code>的对象</td> 
  </tr> 
  <tr> 
   <td><code>notifyItemInserted(int position)</code></td> 
   <td>通知<code>RecyclerView</code>在<code>position</code>处插入一个<code>item</code></td> 
  </tr> 
  <tr> 
   <td><code>notifyItemRangeInserted(int positionStart, int itemCount)</code></td> 
   <td>通知<code>RecyclerView</code>从<code>positionStart</code>开始插入<code>itemCount</code>个<code>item</code></td> 
  </tr> 
 </tbody> 
</table>

有些情况下，方法需要考虑组合使用，否则可能出现`position`错乱，例如

**在Adapter中移除或者插入item**

/**
     * 移除指定Position的Item
     */
    public void remove(int position) {
        if (dataList.size() == 0) return;
        dataList.remove(position);
        notifyItemRemoved(position);
        notifyItemRangeChanged(position, dataList.size() - position);
    }
    
    //在Activity中使用 ，设置点击事件
    adapter.setItemListener(new MyRecyclerViewAdapter.onRecyclerItemClickerListener() {
        @Override
        public void onRecyclerItemClick(View view, Object data, int position) {
            adapter.remove(position);
            // String s = (String) data;
            // adapter.inserted(position,s+"---->hi");
        }
    });
    
    //在指定位置插入一个item
    public void inserted(int position, String s) {
        if (dataList.size() == 0) return;
        dataList.add(position, s);
        notifyItemInserted(position);
        notifyItemRangeChanged(position, dataList.size() - position);
    }

`notifyItemRemoved(position)`虽然通知移除了`RecycelrView`在`position`位置上的`itemA`，但`itemA`之后的一系列`item`也需要进行改变，也需要通知`RecyclerView`进行改变

但这两个方法性能上都有问题，卡顿比较明显，应该会有更好的动态改变或者动态插入`item`的方法，以后学到了再补充

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

## 1.5 简易的封装 ##

**通用的ViewHolder：**

public class BaseViewHolder extends RecyclerView.ViewHolder {
        private final SparseArray<View> sparseArray;
    
        public BaseViewHolder(View itemView) {
            super(itemView);
            this.sparseArray = new SparseArray<>(8); //一般一个Item 不会超过8种控件
        }
    
        public <T extends View> T getView(int viewId) {
            View view = sparseArray.get(viewId);
            if (view == null) {
                view = itemView.findViewById(viewId);
                sparseArray.put(viewId, view);
            }
            return (T) view;
        }
    
        public BaseViewHolder setText(int viewId, String text) {
            TextView tv = getView(viewId);
            if (tv != null) {
                tv.setText(text);
            }
            return this;
        }
    }

主要思路就是使用`SparseArray<View>`将控件存起来

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

**适配器：**

public abstract class CommonBaseAdapter<T> extends RecyclerView.Adapter<BaseViewHolder> {
        protected List<T> data = new ArrayList<>();
        protected int itemLayoutId;
        protected Context mContext;
        private onRecyclerItemClickerListener mListener;
    
        public CommonBaseAdapter(RecyclerView rv, @LayoutRes int itemLayoutId) {
            this.itemLayoutId = itemLayoutId;
            this.mContext = rv.getContext();
        }
    
        public void setData(List<T> data) {
            if (data != null) {
                this.data.clear();
                this.data.addAll(data);
                notifyDataSetChanged();
            }
        }
    
        /**
         *  增加点击监听
         */
        public void setItemListener(onRecyclerItemClickerListener mListener) {
            this.mListener = mListener;
        }
    
        @Override
        public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            //这里使用3个参数的方法
            View view = LayoutInflater.from(mContext).inflate(itemLayoutId, parent, false);
            return new BaseViewHolder(view);
        }
    
        @Override
        public void onBindViewHolder(BaseViewHolder holder, int position) {
            bindViewData(holder, data.get(position), position);
            holder.itemView.setOnClickListener(getOnClickListener(position));
        }
    
        private View.OnClickListener getOnClickListener(final int position) {
            return new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    if (mListener != null && v != null) {
                        mListener.onRecyclerItemClick(v, data.get(position), position);
                    }
                }
            };
        }
    
        @Override
        public int getItemCount() {
            return this.data.size();
        }
    
        public abstract void bindViewData(BaseViewHolder holder, T item, int position);
    
        interface onRecyclerItemClickerListener {
            void onRecyclerItemClick(View view, Object data, int position);
        }
    }

内部提供一个抽象方法`bindViewData()`，子类重写抽象方法来做一些具体的操作。

封装的很简单，但平常学习使用也能减少一些重复代码。网上有很多强大的封装，可以再深入学习一下[为RecyclerView打造通用Adapter让RecyclerView更加好用][RecyclerView_Adapter_RecyclerView]

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

**使用：**

public class RecyclerViewAdapter extends CommonBaseAdapter<String> {
    
        public RecyclerViewAdapter(RecyclerView rv, @LayoutRes int itemLayoutId, @IdRes int resId) {
            super(rv, itemLayoutId);
    
        }
    
        @Override
        public void bindViewData(BaseViewHolder holder, String item, int position) {
            holder.setText(R.id.textViewId, item);
        }
    }

在`Activity`中就可以进行使用

这个简易的封装并没有对添加加载图片的方法。加载图片的方法一开始也我封装在了这个`CommonBaseAdapter`中，但后来发现直接封装在这里并不是好的思路

图片需要做的处理比较多，而且主流的库有3个，为了易于维护，还是将图片的操作单独再封装在一个工具类中，在`CommonBaseAdapter`中使用操作图片的工具类比较好

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

## 1.6 添加HeaderView和FooterViewiew ##

学的鸿洋大神的代码和思路，涉及到了[装饰模式][Link 1]。还有一种添加方式是直接通过使用多种`item`直接在现有的`CommonBaseAdapter`来修改，但感觉这种思路需要对`CommonBaseAdapter`改动的代码太多，点击事件的`position`也需要考虑，不如鸿洋大神的这种思路易于开发和维护

**代码：**

public class HeaderAndFooterAdapter extends RecyclerView.Adapter<BaseViewHolder> {
        private CommonBaseAdapter mAdapter;
    
        private static final int HEADER_VIEW_TYPE = 2 << 6;
        private static final int FOOTER_VIEW_TYPE = 2 << 5;
    
        private SparseArrayCompat<View> mHeaderViews = new SparseArrayCompat<>();
        private SparseArrayCompat<View> mFooterViews = new SparseArrayCompat<>();
    
        public HeaderAndFooterAdapter(CommonBaseAdapter mAdapter) {
            this.mAdapter = mAdapter;
        }
    
        @Override
        public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            if (null != mHeaderViews.get(viewType)) {
                return new HeaderAndFooterHolder(mHeaderViews.get(viewType));
            } else if (null != mFooterViews.get(viewType)) {
                return new HeaderAndFooterHolder(mFooterViews.get(viewType));
            }
            return mAdapter.onCreateViewHolder(parent, viewType);
        }
    
        @Override
        public void onBindViewHolder(BaseViewHolder holder, int position) {
            if (isHeaderViewPosition(position)) return;
            if (isFooterViewPosition(position)) return;
            mAdapter.onBindViewHolder(holder, position - getHeaderViewCount());
        }
    
        @Override
        public int getItemViewType(int position) {
            if (isHeaderViewPosition(position)) {
                return mHeaderViews.keyAt(position);
            } else if (isFooterViewPosition(position)) {
                return mFooterViews.keyAt(position-getHeaderViewCount()-getAdapterItemCount());
            }
            return mAdapter.getItemViewType(position - getHeaderViewCount());
        }
    
        @Override
        public int getItemCount() {
            return getHeaderViewCount() + getFooterViewCount() + getAdapterItemCount();
        }
    
        /**
         * 加入HeaderView
         */
        public void addHeaderView(View view) {
            mHeaderViews.put(mHeaderViews.size() + HEADER_VIEW_TYPE, view);
        }
    
        /**
         * 加入FooterView
         */
        public void addFootView(View view) {
            mFooterViews.put(mFooterViews.size() + FOOTER_VIEW_TYPE, view);
        }
    
        /**
         * HeaderView 的数目
         */
        public int getHeaderViewCount() {
            return mHeaderViews.size();
        }
    
        /**
         * FooterView 的数目
         */
        public int getFooterViewCount() {
            return mFooterViews.size();
        }
    
        /**
         * 是不是HeaderView的Position
         */
        private boolean isHeaderViewPosition(int position) {
            return position < getHeaderViewCount();
        }
    
    
        /**
         * 是不是FooterView的Position
         */
        private boolean isFooterViewPosition(int position) {
            return position >= getHeaderViewCount() + getAdapterItemCount();
        }
    
        /**
         * 得到Adapter中Item的数目
         */
        private int getAdapterItemCount() {
            return mAdapter.getItemCount();
        }
    
        private class HeaderAndFooterHolder extends BaseViewHolder {
            private HeaderAndFooterHolder(View itemView) {
                super(itemView);
            }
        }
    }

封装的思路：  
将`add`进来的`view`进行保存，当加载`item`时，利用`itemType`对`view`进行类型判断，如果是`HeaderView`或者`FooterView`就创建`HeaderAndFooterHolder`，然后绑定只是用来显示并没有对`HeaderView`或者`FooterView`做其他更多事件的处理

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

使用也比较方便：

//数据适配器
    RecyclerViewAdapter adapter = new RecyclerViewAdapter(rv, R.layout.id_rv_item_layout, R.id.tv__id_item_layout);
    //头View适配器
    HeaderAndFooterAdapter headerAndFooterAdapter = new HeaderAndFooterAdapter(adapter);
    //HeaderView
    TextView headerView = new TextView(this);
    headerView.setBackgroundColor(Color.BLACK);
    headerView.setTextColor(Color.WHITE);
    headerView.setWidth(1080);
    headerView.setTextSize(50);
    headerView.setText("我是头");
    headerAndFooterAdapter.addHeaderView(headerView);
    //设置适配器
    rv.setAdapter(headerAndFooterAdapter);
    //添加数据
    addData(adapter);

![format_png 1][]

添加HeaderView

`RecyelrView`设置的适配器是`headerAndFooterAdapter`，而添加数据使用的是`adapter`。`HeaderAndFooterAdapter`是支持添加多个`HeaderView`的

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

### 1.6.1 GridLayoutManger和StaggeredGridLayoutManager跨列问题 ###

上面添加`HeaderView`时，使用的`LinerLayoutManager`，当使用`GridLayoutManger`时，便会有问题

**HeaderView不能单独占据一行**

![format_png 2][]

GridLayoutManager遇到问题

**加入针对GridLayoutManager跨列处理的代码：**

/**
     *当RecyelrView开始观察Adapter会被回调
     */
    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        mAdapter.onAttachedToRecyclerView(recyclerView);
        final RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
        if (manager instanceof GridLayoutManager) {
            final GridLayoutManager gridLayoutManager = (GridLayoutManager) manager;
            gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                @Override
                public int getSpanSize(int position) {
                    int viewType = getItemViewType(position);
                    //如果是HeaderView或者是FooterView，设置占据gridLayoutManager.getSpanCount()列
                    if (null != mHeaderViews.get(viewType) || null != mFooterViews.get(viewType)) {
                        return gridLayoutManager.getSpanCount();
                    }
                    return 1;
                }
            });
        }
    }

![format_png 3][]

跨列处理

当布局管理器为`GridLayouManger`时，对当前要的添加的`item`进行判断，如果是HeaderView或者是FooterView，就进行跨列处理，单独占据一行

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

**加入针对StaggeredGridLayoutManager跨列处理的代码：**

/**
     * 一个item通过adapter开始显示会被回调
     */
    @Override
    public void onViewAttachedToWindow(BaseViewHolder holder) {
        super.onViewAttachedToWindow(holder);
        int position = holder.getLayoutPosition();
        if (isHeaderViewPosition(position)||isFooterViewPosition(position)){
            ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
            if (null != lp && lp instanceof StaggeredGridLayoutManager.LayoutParams){
                StaggeredGridLayoutManager.LayoutParams p = (StaggeredGridLayoutManager.LayoutParams) lp;
                p.setFullSpan(true);//占满一行
            }
        }
    }

![format_png 4][]

瀑布流跨列

当布局管理器为`StaggeredGridLayoutManager`时，对当前要的添加的`item`进行判断，如果是HeaderView或者是FooterView，就设置`setFullSpan(true)`，占满一行

学习资料：

*  [为RecyclerView打造通用Adapter让RecyclerView更加好用][RecyclerView_Adapter_RecyclerView]
 *  [Android优雅的为RecyclerView添加HeaderView和FooterView][Android_RecyclerView_HeaderView_FooterView]

[format_png]: /images/20230209/2e1b3aa62c724f7b94a8c75ecf8b994f.png
[aHR0cHM6Ly91cGxvYWQtaW1hZ2VzLmppYW5zaHUuaW8vdXBsb2FkX2ltYWdlcy8yMDg2NjgyLTQyMGFiODBmZTVkZjU4NjcuZ2lm]: /images/20230209/c9f38b72d5524c73bbe9c5f67e1258a6.png
[RecyclerView_Item]: https://link.jianshu.com/?t=http%3A%2F%2Fblog.devwiki.net%2Findex.php%2F2016%2F07%2F24%2Fthree-ways-click-recyclerview-item.html
[RecyclerView_Adapter_RecyclerView]: https://link.jianshu.com/?t=http%3A%2F%2Fblog.csdn.net%2Flmj623565791%2Farticle%2Fdetails%2F51118836
[Link 1]: https://link.jianshu.com/?t=http%3A%2F%2Flavasoft.blog.51cto.com%2F62575%2F90853%2F
[format_png 1]: /images/20230209/5649354d98fe4a36ae795e68cc093860.png
[format_png 2]: /images/20230209/1495b6df49e643879a02284b100ae470.png
[format_png 3]: /images/20230209/c6c1114d7ccf4b6387e5c04b56bf5a2e.png
[format_png 4]: /images/20230209/6aa8d7b8fd254a30947f9a65d2bc5170.png
[Android_RecyclerView_HeaderView_FooterView]: https://link.jianshu.com/?t=http%3A%2F%2Fblog.csdn.net%2Flmj623565791%2Farticle%2Fdetails%2F51854533