Java 在扩展RecyclerView.Adapter时使用装饰器模式合适吗？

我已经编写了一个

footer适配器

，它似乎工作得很好

我意识到，

ViewHolder

有一个字段

mPosition

，其中包含每个元素中的状态，这让我怀疑使用Decorator模式无法实现标题，因为它在每个

适配器中都会保持不同的位置

也就是说，除非包装器/装饰器
适配器
没有改变其他元素。也就是说：页脚是可以的，只要数据不需要绑定到页脚

如果包装适配器是可能的，那么我们将需要更多的访问ViewHolder？我不知道这些田地是怎么回事

预期用途：

headerView = new View( context );
footerView = new View( context );

MyAdapter myAdapter = new MyAdapter();
HeaderAdapter headerAdapter = new HeaderAdapter( myAdapter , headerView );
FooterAdapter footerAdapter = new FooterAdapter( headerAdapter , footerView );

RecyclerView recyclerView = new RecyclerView();
recyclerView.setAdapter( footerAdapter );

这将非常酷，因为这样我们就可以向任意
适配器添加页眉和页脚，而不必担心索引和抵消项目计数

FooterAdapter.java

public class FooterAdapter extends RecyclerView.Adapter
{
    private static final String TAG = "FooterAdapter";
    private final RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter;

    private View footer;

    public static final int FOOTER_TYPE = 0x72846fe;

    public FooterAdapter( RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter , View footer )
    {
        this.footer = footer;
        this.wrappedAdapter = wrappedAdapter;
        wrappedAdapter.registerAdapterDataObserver(new ThisObserver());
    }

    @Override
    public int getItemViewType(int position)
    {
        if( position == wrappedAdapter.getItemCount() ) return FOOTER_TYPE;
        return wrappedAdapter.getItemViewType(position);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if( viewType == FOOTER_TYPE )
        {
            return new RecyclerView.ViewHolder( footer ){};
        }else
        {
            return wrappedAdapter.onCreateViewHolder(parent,viewType);
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if( holder.getItemViewType() == FOOTER_TYPE ) return;
        return wrappedAdapter.bindViewHolder( holder , position );
    }

    @Override
    public int getItemCount() {
        return wrappedAdapter.getItemCount() + 1;
    }


    private class ThisObserver extends AdapterDataObserver
    {
        public void onChanged() {
            notifyDataSetChanged();
        }

        public void onItemRangeChanged(int positionStart, int itemCount) {
            notifyItemRangeChanged(positionStart,itemCount);
        }

        public void onItemRangeInserted(int positionStart, int itemCount) {
            notifyItemRangeInserted(positionStart,itemCount);
        }

        public void onItemRangeRemoved(int positionStart, int itemCount) {
            notifyItemRangeRemoved(positionStart,itemCount);
        }

        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            int lower = Math.min( fromPosition , toPosition );
            int upper = Math.max( fromPosition , toPosition );
            for( int i = itemCount-1 ; i < itemCount ; i++ )
            {
                notifyItemMoved(upper+i,lower+i+(toPosition-fromPosition));
            }
        }
    }
}

public class HeaderAdapter extends RecyclerView.Adapter
{
    private static final String TAG = "HeaderAdapter";
    private final RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter;

    private View header;

    public static final int HEADER_TYPE = 0x747efe;

    public HeaderAdapter( RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter , View header )
    {
        this.header = header;
        this.wrappedAdapter = wrappedAdapter;
        wrappedAdapter.registerAdapterDataObserver(new ThisObserver());
    }

    @Override
    public int getItemViewType(int position)
    {
        return position == 0 ? HEADER_TYPE : wrappedAdapter.getItemViewType(position - 1);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if( viewType == HEADER_TYPE )
        {
            return new RecyclerView.ViewHolder( header ){};
        }else
        {
            return new RecyclerView.ViewHolder( wrappedAdapter.onCreateViewHolder(parent,viewType).itemView ){};
            // I thought some kind of wrapping (hack?) like this might get 
            // around the different indexing in different Adapters, but 
            // it doesn't work, it would probably needs more 
            // information, or to be able to observe changes in 
            // the "child" ViewHolder.
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if( holder.getItemViewType() != HEADER_TYPE ) wrappedAdapter.bindViewHolder( holder , position - 1 );
    }

    @Override
    public int getItemCount() {
        return wrappedAdapter.getItemCount() + 1;
    }


    private class ThisObserver extends RecyclerView.AdapterDataObserver
    {

        public void onChanged() {
            notifyDataSetChanged();
        }

        public void onItemRangeChanged(int positionStart, int itemCount) {
            notifyItemRangeChanged(1+positionStart,itemCount);
        }

        public void onItemRangeInserted(final int positionStart, final int itemCount) {
            notifyItemRangeInserted(1 + positionStart, itemCount);
        }

        public void onItemRangeRemoved(int positionStart, int itemCount) {
            notifyItemRangeRemoved(1 + positionStart, itemCount);
        }

        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            fromPosition++;
            toPosition++;
            int lower = Math.min( fromPosition , toPosition );
            int upper = Math.max( fromPosition , toPosition );
            for( int i = itemCount-1 ; i < itemCount ; i++ ) notifyItemMoved(upper+i,lower+i+(toPosition-fromPosition));
        }
    }
}

公共类FooterAdapter扩展了RecyclerView.Adapter
{
私有静态最终字符串TAG=“FooterAdapter”；
专用最终回收视图。适配器wrappedAdapter；
私有视图页脚；
公共静态最终整型页脚类型=0x72846fe；
公共页脚适配器（RecyclerView.Adapter wrappedAdapter，视图页脚）
{
this.footer=页脚；
this.wrappedAdapter=wrappedAdapter；
registerAdapterDataObserver（新的ThisObserver（））；
}
@凌驾
public int getItemViewType（int位置）
{
if（position==wrappedAdapter.getItemCount（））返回页脚类型；
返回wrappedAdapter.getItemViewType（位置）；
}
@凌驾
public RecyclerView.ViewHolder onCreateViewHolder（视图组父级，int-viewType）{
如果（视图类型==页脚类型）
{
返回新的RecyclerView.ViewHolder（页脚）{}；
}否则
{
返回wrappedAdapter.onCreateViewHolder（父级，viewType）；
}
}
@凌驾
BindViewHolder上的公共无效（RecyclerView.ViewHolder，int位置）{
if（holder.getItemViewType（）=页脚类型）返回；
返回wrappedAdapter.bindViewHolder（支架，位置）；
}
@凌驾
public int getItemCount（）{
返回wrappedAdapter.getItemCount（）+1；
}
私有类ThisObserver扩展AdapterDataObserver
{
更改后的公共无效（）{
notifyDataSetChanged（）；
}
已更改公共位置（int positionStart、int itemCount）{
notifyItemRangeChanged（位置开始，itemCount）；
}
已插入的公用项目（int positionStart、int itemCount）{
notifyItemRangeInserted（positionStart，itemCount）；
}
已删除的公共void（int positionStart，int itemCount）{
notifyItemRangeRemoved（positionStart，itemCount）；
}
已移动的公用文件夹（int-fromPosition、int-toPosition、int-itemCount）{
int lower=数学最小值（起始位置、位置）；
int upper=数学最大值（起始位置、位置）；
对于（int i=itemCount-1；i

HeaderAdapter.java

public class FooterAdapter extends RecyclerView.Adapter
{
    private static final String TAG = "FooterAdapter";
    private final RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter;

    private View footer;

    public static final int FOOTER_TYPE = 0x72846fe;

    public FooterAdapter( RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter , View footer )
    {
        this.footer = footer;
        this.wrappedAdapter = wrappedAdapter;
        wrappedAdapter.registerAdapterDataObserver(new ThisObserver());
    }

    @Override
    public int getItemViewType(int position)
    {
        if( position == wrappedAdapter.getItemCount() ) return FOOTER_TYPE;
        return wrappedAdapter.getItemViewType(position);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if( viewType == FOOTER_TYPE )
        {
            return new RecyclerView.ViewHolder( footer ){};
        }else
        {
            return wrappedAdapter.onCreateViewHolder(parent,viewType);
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if( holder.getItemViewType() == FOOTER_TYPE ) return;
        return wrappedAdapter.bindViewHolder( holder , position );
    }

    @Override
    public int getItemCount() {
        return wrappedAdapter.getItemCount() + 1;
    }


    private class ThisObserver extends AdapterDataObserver
    {
        public void onChanged() {
            notifyDataSetChanged();
        }

        public void onItemRangeChanged(int positionStart, int itemCount) {
            notifyItemRangeChanged(positionStart,itemCount);
        }

        public void onItemRangeInserted(int positionStart, int itemCount) {
            notifyItemRangeInserted(positionStart,itemCount);
        }

        public void onItemRangeRemoved(int positionStart, int itemCount) {
            notifyItemRangeRemoved(positionStart,itemCount);
        }

        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            int lower = Math.min( fromPosition , toPosition );
            int upper = Math.max( fromPosition , toPosition );
            for( int i = itemCount-1 ; i < itemCount ; i++ )
            {
                notifyItemMoved(upper+i,lower+i+(toPosition-fromPosition));
            }
        }
    }
}

public class HeaderAdapter extends RecyclerView.Adapter
{
    private static final String TAG = "HeaderAdapter";
    private final RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter;

    private View header;

    public static final int HEADER_TYPE = 0x747efe;

    public HeaderAdapter( RecyclerView.Adapter<RecyclerView.ViewHolder> wrappedAdapter , View header )
    {
        this.header = header;
        this.wrappedAdapter = wrappedAdapter;
        wrappedAdapter.registerAdapterDataObserver(new ThisObserver());
    }

    @Override
    public int getItemViewType(int position)
    {
        return position == 0 ? HEADER_TYPE : wrappedAdapter.getItemViewType(position - 1);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if( viewType == HEADER_TYPE )
        {
            return new RecyclerView.ViewHolder( header ){};
        }else
        {
            return new RecyclerView.ViewHolder( wrappedAdapter.onCreateViewHolder(parent,viewType).itemView ){};
            // I thought some kind of wrapping (hack?) like this might get 
            // around the different indexing in different Adapters, but 
            // it doesn't work, it would probably needs more 
            // information, or to be able to observe changes in 
            // the "child" ViewHolder.
        }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if( holder.getItemViewType() != HEADER_TYPE ) wrappedAdapter.bindViewHolder( holder , position - 1 );
    }

    @Override
    public int getItemCount() {
        return wrappedAdapter.getItemCount() + 1;
    }


    private class ThisObserver extends RecyclerView.AdapterDataObserver
    {

        public void onChanged() {
            notifyDataSetChanged();
        }

        public void onItemRangeChanged(int positionStart, int itemCount) {
            notifyItemRangeChanged(1+positionStart,itemCount);
        }

        public void onItemRangeInserted(final int positionStart, final int itemCount) {
            notifyItemRangeInserted(1 + positionStart, itemCount);
        }

        public void onItemRangeRemoved(int positionStart, int itemCount) {
            notifyItemRangeRemoved(1 + positionStart, itemCount);
        }

        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            fromPosition++;
            toPosition++;
            int lower = Math.min( fromPosition , toPosition );
            int upper = Math.max( fromPosition , toPosition );
            for( int i = itemCount-1 ; i < itemCount ; i++ ) notifyItemMoved(upper+i,lower+i+(toPosition-fromPosition));
        }
    }
}

公共类HeaderAdapter扩展了RecyclerView.Adapter
{
私有静态最终字符串标记=“HeaderAdapter”；
专用最终回收视图。适配器wrappedAdapter；
私有视图头；
公共静态最终整数头类型=0x747efe；
公共标头适配器（RecyclerView.Adapter wrappedAdapter，视图标头）
{
this.header=头；
this.wrappedAdapter=wrappedAdapter；
registerAdapterDataObserver（新的ThisObserver（））；
}
@凌驾
public int getItemViewType（int位置）
{
返回位置==0？标题类型：wrappedAdapter.getItemViewType（位置-1）；
}
@凌驾
public RecyclerView.ViewHolder onCreateViewHolder（视图组父级，int-viewType）{
如果（视图类型==标题类型）
{
返回新的RecyclerView.ViewHolder（头）{}；
}否则
{
返回新的RecyclerView.ViewHolder（wrappedAdapter.onCreateViewHolder（父级，viewType.itemView）{}；
//我想像这样的包装（黑客？）可能会
//围绕不同适配器中的不同索引，但是
//它不起作用，可能需要更多
//信息，或能够观察到
//“子”视图持有者。
}
}
@凌驾
BindViewHolder上的公共无效（RecyclerView.ViewHolder，int位置）{
if（holder.getItemViewType（）！=HEADER\u TYPE）wrappedAdapter.bindViewHolder（holder，位置-1）；
}
@凌驾
public int getItemCount（）{
返回wrappedAdapter.getItemCount（）+1；
}
私有类ThisObserver扩展了RecyclerView.AdapterDataObserver
{
更改后的公共无效（）{
notifyDataSetChanged（）；
}
已更改公共位置（int positionStart、int itemCount）{
notifyItemRangeChanged（1+positionStart，itemCount）；
}
插入的公共无效项（最终整型位置开始，最终整型项目计数）{
notifyItemRangeInserted（1+positionStart，itemCount）；
}
已删除的公共void（int positionStart，int itemCount）{
notifyItemRangeRemoved（1+positionStart，itemCount）；
}
已移动的公用文件夹（int-fromPosition、int-toPosition、int-itemCount）{
fromPosition++；
拓扑学++；
int lower=数学最小值（起始位置、位置）；
int upper=数学最大值（起始位置、位置）；
对于（inti=itemCount-1；i