高级UI之RecyclerView头部和尾部添加

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在ListView中，可以添加头部和尾部，其添加方法也是十分的简单，直接调用listview.addHeaderView(view);和listview.addFooterView(view);即可，但在RecyclerView中却没有这样的方法，那么要在RecyclerView中使用这种方法怎么办呢，这就是本文要讲明的地方

原理

查看ListView源代码，得知其头部和尾部，实质上就是对原来的adapter添加了一个头和一个尾，也就是包装了一层，那么我们要在RecyclerView中使用头部和尾部的话，可以按照ListView的方法，依葫芦画瓢做一个头，做一个尾

实现

自定义一个RecyclerView布局，增加头部和尾部的添加方法

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public class WrapRecyclerView extends RecyclerView {

    private ArrayList<View> mHeaderViewInfos = new ArrayList<View>();
    private ArrayList<View> mFooterViewInfos = new ArrayList<View>();
    private Adapter mAdapter;

    public WrapRecyclerView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public void addHeaderView(View v) {
        mHeaderViewInfos.add(v);
        if (mAdapter != null) {
            if (!(mAdapter instanceof HeaderViewRecyclerAdapter)) {
                mAdapter = new HeaderViewRecyclerAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
            }
        }
    }

    public void addFooterView(View v) {
        mFooterViewInfos.add(v);
        if (mAdapter != null) {
            if (!(mAdapter instanceof HeaderViewRecyclerAdapter)) {
                mAdapter = new HeaderViewRecyclerAdapter(mHeaderViewInfos, mFooterViewInfos, mAdapter);
            }
        }
    }

    @Override
    public void setAdapter(Adapter adapter) {
        if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
            mAdapter = new HeaderViewRecyclerAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);
        } else {
            mAdapter = adapter;
        }
        super.setAdapter(mAdapter);
    }
}

布局中使用到的适配器

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public class HeaderViewRecyclerAdapter extends Adapter {
    private Adapter mAdapter;
    ArrayList<View> mHeaderViewInfos;
    ArrayList<View> mFooterViewInfos;

    public HeaderViewRecyclerAdapter(ArrayList<View> headerViewInfos,
                                     ArrayList<View> footerViewInfos, Adapter adapter) {
        mAdapter = adapter;
        if (headerViewInfos == null) {
            mHeaderViewInfos = new ArrayList<View>();
        } else {
            mHeaderViewInfos = headerViewInfos;
        }
        if (footerViewInfos == null) {
            mFooterViewInfos = new ArrayList<View>();
        } else {
            mFooterViewInfos = footerViewInfos;
        }
    }

    @Override
    public int getItemCount() {
        if (mAdapter != null) {
            return getFootersCount() + getHeadersCount() + mAdapter.getItemCount();
        } else {
            return getFootersCount() + getHeadersCount();
        }
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        int numHeaders = getHeadersCount();
        //head
        if (position < numHeaders) {
            return;
        }
        //body
        final int adjPosition = position - numHeaders;
        int adapterCount = 0;
        if (mAdapter != null) {
            adapterCount = mAdapter.getItemCount();
            if (adjPosition < adapterCount) {
                mAdapter.onBindViewHolder(holder, adjPosition);
                return;
            }
        }
        //footer
    }

    @Override
    public int getItemViewType(int position) {
        //判断当前条目是什么类型
        int numHeaders = getHeadersCount();
        if (position < numHeaders) {
            return RecyclerView.INVALID_TYPE;
        }
        final int adjPosition = position - numHeaders;
        int adapterCount = 0;
        if (mAdapter != null) {
            adapterCount = mAdapter.getItemCount();
            if (adjPosition < adapterCount) {
                return mAdapter.getItemViewType(adjPosition);
            }
        }
        return RecyclerView.INVALID_TYPE - 1;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        //header
        if (viewType == RecyclerView.INVALID_TYPE) {
            return new HeaderViewHolder(mHeaderViewInfos.get(0));
        } else if (viewType == RecyclerView.INVALID_TYPE - 1) {//footer
            return new HeaderViewHolder(mFooterViewInfos.get(0));
        }
        //Footer
        return mAdapter.onCreateViewHolder(parent, viewType);
    }

    public int getHeadersCount() {
        return mHeaderViewInfos.size();
    }

    public int getFootersCount() {
        return mFooterViewInfos.size();
    }

    private static class HeaderViewHolder extends ViewHolder {
        public HeaderViewHolder(View view) {
            super(view);
        }
    }
}

在布局文件中使用增加的自定义布局

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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.cj5785.wraprecyclerview.WrapRecyclerView
        android:id="@+id/wrap_recyclerview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

编写适配器

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public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private List<String> list;

    public MyAdapter(List<String> list) {
        this.list = list;
    }

    class MyViewHolder extends RecyclerView.ViewHolder{
        private TextView textView;
        public MyViewHolder(View view) {
            super(view);
            textView = (TextView) view.findViewById(R.id.tv);
        }
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View view = layoutInflater.inflate(R.layout.list_item,parent,false);
        MyViewHolder holder = new MyViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.textView.setText(list.get(position));
    }

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

适配器的Item布局

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<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tv"
    android:layout_marginTop="10dp"
    android:layout_marginBottom="10dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center" />

在主活动在调用

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public class MainActivity extends AppCompatActivity {

    private WrapRecyclerView wrapRecyclerView;
    private LayoutParams params;
    private List<String> list;
    private MyAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        wrapRecyclerView = (WrapRecyclerView) findViewById(R.id.wrap_recyclerview);
        params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
        TextView header = new TextView(this);
        header.setGravity(Gravity.CENTER);
        header.setLayoutParams(params);
        header.setText("Header");
        wrapRecyclerView.addHeaderView(header);
        TextView footer = new TextView(this);
        footer.setGravity(Gravity.CENTER);
        footer.setLayoutParams(params);
        footer.setText("Footer");
        wrapRecyclerView.addFooterView(footer);
        list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            list.add("item " + i);
        }
        adapter = new MyAdapter(list);
        wrapRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        wrapRecyclerView.setAdapter(adapter);
    }
}

运行结果

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