RecyclerView的使用（3）之加入Header和Footer

原创文章。转载请注明 http://blog.csdn.net/leejizhou/article/details/50742544 李济洲的博客

RecyclerView尽管作为ListView的替代者有着较好的性能提升。可是ListView的一些经常使用功能却没有提供，比方我们平时会经经常使用到的addHeaderView，addFooterView，既然RecyclerView没有提供这种方法，我们应该怎样为列表加入头部和底部呢？通过看ListView的源代码能够知道ListView的加入Header和Footer是靠Adapter里面动态加入的。所以我们依照这个思路也给RecyclerView加入HeaderView和FooterView。先看一下效果

假设你还不了解RecyclerView怎样使用。能够看一下前几篇博文

RecyclerView的使用（1）之HelloWorld

RecyclerView的使用（2）之多Item布局的载入

RecyclerView实现加入HeaderView和FooterView的核心就是在Adapter里面的onCreateViewHolder依据viewType来推断是列表项还是HeaderView来分别载入不同的布局文件。当然viewType的推断规则也是由我们定义的。废话不多说，看一下详细的实现效果。

1：Gradle配置 build.gradle

 compile 'com.android.support:recyclerview-v7:23.1.1'
 compile 'com.android.support:cardview-v7:23.1.1'

2：主布局文件 activity_main.xml 非常easy里面一个RecyclerView

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <android.support.v7.widget.RecyclerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/rv_list"
        />
</LinearLayout>

3：列表项布局 rv_item.xml 外面一个CardView的卡片式容器里面一个TextView

<?xml version="1.0" encoding="utf-8"?

>
<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp"
    android:id="@+id/cv_item"
    android:foreground="?

android:attr/selectableItemBackground"
    card_view:cardCornerRadius="4dp"
    card_view:cardElevation="4dp"
    >
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/tv_item_text"
            android:text="test"
            android:layout_margin="8dp"
            />
    </LinearLayout>

</android.support.v7.widget.CardView>

4：列表头部布局 rv_header.xml

<?

xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp"
    android:id="@+id/cv_item"
    android:foreground="?

android:attr/selectableItemBackground"
    card_view:cardCornerRadius="4dp"
    card_view:cardElevation="4dp"
    card_view:cardBackgroundColor="#4CAF50"
    >
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="150dp"
        >
        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="Header"
            android:textSize="30sp"
            android:textColor="#ffffff"
            android:gravity="center"
            />
    </LinearLayout>
</android.support.v7.widget.CardView>

5：列表底部布局 rv_footer.xml

<?xml version="1.0" encoding="utf-8"?

>
<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp"
    android:id="@+id/cv_item"
    android:foreground="?

android:attr/selectableItemBackground"
    card_view:cardCornerRadius="4dp"
    card_view:cardElevation="4dp"
    card_view:cardBackgroundColor="#E91E63"
    >
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="150dp"
        >
        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="Footer"
            android:textSize="30sp"
            android:textColor="#ffffff"
            android:gravity="center"
            />

    </LinearLayout>
</android.support.v7.widget.CardView>

6：*HeaderBottomAdapter.java，RecyclerView的Adapter，在getItemViewType方法里面推断了当前Item的类型。然后在onCreateViewHolder跟据item的类型分别载入不同的布局以实现HeaderView和FooterView，其它方法的含义能够參考凝视

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

/**
 * Created by Lijizhou on 2016/2/24.
 * Blog:http://blog.csdn.net/leejizhou
 * QQ:3107777777
 */
public class HeaderBottomAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    //item类型
    public static final int ITEM_TYPE_HEADER = 0;
    public static final int ITEM_TYPE_CONTENT = 1;
    public static final int ITEM_TYPE_BOTTOM = 2;
    //模拟数据
    public String [] texts={"java","python","C++","Php",".NET","js","Ruby","Swift","OC"};
    private LayoutInflater mLayoutInflater;
    private Context mContext;
    private int mHeaderCount=1;//头部View个数
    private int mBottomCount=1;//底部View个数

    public HeaderBottomAdapter(Context context) {
        mContext = context;
        mLayoutInflater = LayoutInflater.from(context);
    }

    //内容长度
    public int getContentItemCount(){
        return texts.length;
    }
    //推断当前item是否是HeadView
    public boolean isHeaderView(int position) {
        return mHeaderCount != 0 && position < mHeaderCount;
    }
    //推断当前item是否是FooterView
    public boolean isBottomView(int position) {
        return mBottomCount != 0 && position >= (mHeaderCount + getContentItemCount());
    }

    //推断当前item类型
    @Override
    public int getItemViewType(int position) {
        int dataItemCount = getContentItemCount();
        if (mHeaderCount != 0 && position < mHeaderCount) {
            //头部View
            return ITEM_TYPE_HEADER;
        } else if (mBottomCount != 0 && position >= (mHeaderCount + dataItemCount)) {
            //底部View
            return ITEM_TYPE_BOTTOM;
        } else {
            //内容View
            return ITEM_TYPE_CONTENT;
        }
    }

    //内容 ViewHolder
    public static class ContentViewHolder extends RecyclerView.ViewHolder {
        private TextView textView;
        public ContentViewHolder(View itemView) {
            super(itemView);
            textView=(TextView)itemView.findViewById(R.id.tv_item_text);
        }
    }
    //头部 ViewHolder
    public static class HeaderViewHolder extends RecyclerView.ViewHolder {

        public HeaderViewHolder(View itemView) {
            super(itemView);
        }
    }
    //底部 ViewHolder
    public static class BottomViewHolder extends RecyclerView.ViewHolder {

        public BottomViewHolder(View itemView) {
            super(itemView);
        }
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType ==ITEM_TYPE_HEADER) {
            return new HeaderViewHolder(mLayoutInflater.inflate(R.layout.rv_header, parent, false));
        } else if (viewType == ITEM_TYPE_CONTENT) {
            return  new ContentViewHolder(mLayoutInflater.inflate(R.layout.rv_item, parent, false));
        } else if (viewType == ITEM_TYPE_BOTTOM) {
            return new BottomViewHolder(mLayoutInflater.inflate(R.layout.rv_footer, parent, false));
        }
        return null;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof HeaderViewHolder) {

        } else if (holder instanceof ContentViewHolder) {
            ((ContentViewHolder) holder).textView.setText(texts[position - mHeaderCount]);

        } else if (holder instanceof BottomViewHolder) {

        }
    }

    @Override
    public int getItemCount() {
       return mHeaderCount + getContentItemCount() + mBottomCount;
    }

}

7：最后一步。MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public class MainActivity extends AppCompatActivity {
    private RecyclerView mRecyclerView;
    private HeaderBottomAdapter adapter;
    GridLayoutManager gridLayoutManager;
    LinearLayoutManager layoutManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRecyclerView=(RecyclerView)findViewById(R.id.rv_list);
        //List布局
        layoutManager=new LinearLayoutManager(this);
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(layoutManager);
        mRecyclerView.setAdapter(adapter=new HeaderBottomAdapter(this));

        //Grid布局
//        gridLayoutManager=new GridLayoutManager(MainActivity.this, 2);
//        mRecyclerView.setLayoutManager(gridLayoutManager);//这里用线性宫格显示 相似于grid view
//        mRecyclerView.setAdapter(adapter=new HeaderBottomAdapter(this));
//
//
//            gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
//                @Override
//                public int getSpanSize(int position) {
//                    return (adapter.isHeaderView(position) || adapter.isBottomView(position)) ?

gridLayoutManager.getSpanCount() : 1;
//                }
//            });

    }

}

这里注意一点。假设你的RecyclerView使用Grid类型列表在设置Adapter后须要调用这种方法，依据当前Item类型来推断占领的横向格数，这也是Adapter里面实现isHeaderView和isBottomView的缘故

 gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
                @Override
                public int getSpanSize(int position) {
                    return (adapter.isHeaderView(position) || adapter.isBottomView(position)) ? gridLayoutManager.getSpanCount() : 1;
                }
           });

Ok，RecyclerView加入Header和Footer就这样轻松实现了，你也能够把Adapter再次封装更有利于日常的开发，本篇博文的源代码下载地址 下载地址