RecyclerView添加头部和尾部

为RecyclerView添加头部和底部

第一步1

需要定义一个Adapter,继承自RecyclerView.Adapter

HeaderAndFooterWrapper<T> extends RecyclerView.Adapter<RecyclerView.ViewHolder>

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第二步2

在Adapter的构造方法中传入一个Adapter对象用于添加除头部尾部以外的item,并生命所需要用的成员变量

private static final int BASE_ITEM_TYPE_HEADER = 10000;    private static final int BASE_ITEM_TYPE_FOOTER = 20000;    private SparseArrayCompat<View> mHeaderViews = new SparseArrayCompat<>();    private SparseArrayCompat<View> mFootViews = new SparseArrayCompat<>();    private RecyclerView.Adapter mInnerAdapter;    public HeaderAndFooterWrapper(RecyclerView.Adapter mInnerAdapter) {        this.mInnerAdapter = mInnerAdapter;    }    public boolean isHeaderViewPos(int position){        return position < getHeadersCount();    }

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第三步3

需要有添加头部和尾部的方法,以及判断当前item是否是头部和尾部视图

public boolean isFooterViewPos(int position){        return position >= getHeadersCount() + getRealItemCount();    }    public void addHeaderView(View view){        mHeaderViews.put(mHeaderViews.size() + BASE_ITEM_TYPE_HEADER,view);    }    public void addFooterView(View view){        mFootViews.put(mFootViews.size() + BASE_ITEM_TYPE_FOOTER,view);    }

第四步4

添加获取每一种item数量的方法,比如header视图数量或者footer视图数量

  private int getRealItemCount() {        return mInnerAdapter.getItemCount();    }    private int getHeadersCount() {        return mHeaderViews.size();    }    private int getFootersCount() {        return mFootViews.size();    }     @Override    public int getItemCount() {        return getHeadersCount() + getRealItemCount() + getFootersCount();    }

第五步5

复写getItemViewType方法,在该方法中判断如果是头部或者尾部视图就返回其在
private SparseArrayCompat mHeaderViews = new SparseArrayCompat<>();
private SparseArrayCompat mFootViews = new SparseArrayCompat<>();中的下标,以便获取

@Override    public int getItemViewType(int position) {        if(isHeaderViewPos(position)){            return mHeaderViews.keyAt(position);        }else if(isFooterViewPos(position)){            //如果当前是footerview 就计算出其在footerViews中的下标位置            return mFootViews.keyAt(position - getHeadersCount() - getRealItemCount());        }        return mInnerAdapter.getItemViewType(position - getHeadersCount());    }

第六步6

复写onCreateViewHolder方法,和onBindViewHolder方法

 @Override    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {        if(mHeaderViews.get(viewType) != null){            ViewHolder vh = ViewHolder.crateViewHolder(parent.getContext(),                    mHeaderViews.get(viewType));            return vh;        }else if(mFootViews.get(viewType) != null){            ViewHolder vh = ViewHolder.crateViewHolder(parent.getContext(),                    mFootViews.get(viewType));            return vh;        }        return mInnerAdapter.onCreateViewHolder(parent,viewType);    }    @Override    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {        if(isHeaderViewPos(position)){            return;        }else if(isFooterViewPos(position)){            return;        }        mInnerAdapter.onBindViewHolder(holder,position - getHeadersCount());    }

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到此已经完成了添加头部的基本代码,但是如果需要在宫格布局下head依然占据一行的话需要添加一下代码

复写onAttachedToRecyclerView方法,在该方法中判断是否是GridLayoutManger,getSpanCount意思在构造GridLayoutManger的时候所传入的每行item数量,返回值的意思就是代表当前view所需要占据多少个item

 @Override    public void onAttachedToRecyclerView(RecyclerView recyclerView) {        mInnerAdapter.onAttachedToRecyclerView(recyclerView);        final RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();        if(layoutManager instanceof GridLayoutManager){            final GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;            gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {                @Override                public int getSpanSize(int position) {                    int viewType = getItemViewType(position);                    if(mHeaderViews.get(viewType) != null){                        return ((GridLayoutManager) layoutManager).getSpanCount();                    }else if(mFootViews.get(viewType) != null){                        return ((GridLayoutManager) layoutManager).getSpanCount();                    }                    return 1;                }            });            gridLayoutManager.setSpanCount(gridLayoutManager.getSpanCount());        }    }

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代码github地址