RecyclerView添加addHeader和addFooter方法
在新版本的android系统中RecyclerView作为ListView的优化版本，封装了ViewHolder，这样就可以更加方便的使用这个控件。但是相比较ListView，RecyclerView没有提供相应的addHeaderView和addFooterView方法，我们知道在一些下拉控件的实现中，都是设置了headerView或者是footerView，然后不断的设置padding来实现的。那既然RecyclerView没有addHeaderView和addFooterView这些方法，那么是不是就不能实现下拉刷新这样的功能了呢？当然不是。下面就带大家实现一个简易的实现addHeaderView和addFooterView的方法。
我们知道像需要适配器的这些控件，它们的数据都是通过Adapter的提供的。那么我们就着手改造我们的Adapter。首先我们创建一个自定义的Adapter类继承RecyclerView.Adapter
public class HeaderRecyclerViewAdapter extends RecyclerView.Adapter<HeaderRecyclerViewAdapter
.HeaderViewHolder> {
//header view type的开始值
private final int RECYCLER_HEADER_TYPE_BASE = 0xff11;
//footer view type的开始值
private final int RECYCLER_FOOTER_TYPE_BASE = 0xff22;
//header和footer的id值
private final int RECYCLER_HEADER_FOOTER_ID = -1;
//用来存放所有的header view的信息
private List<FixedInfo> mHeaders = new ArrayList<>();
//用来存放所有的footer view的信息
private List<FixedInfo> mFooters = new ArrayList<>();
//保存使用默认的RecyclerView.Adapter创建的adapter的值，这个值必须获取到
private RecyclerView.Adapter mAdapter = null;
public HeaderRecyclerViewAdapter() {
}
public HeaderRecyclerViewAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
public void setAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}我们创建一个HeaderRecyclerViewAdapter类用来包装我们原始的RecyclerView.Adapter类，mAdpter就是对这个原始类的应用。同样创建了两个ArrayList用来保存我们的Headers和footers，这里面有一个FixedInfo类，这个类是干嘛的呢？
//用来保存footer和headers的信息
private class FixedInfo {
public View view;
public int type;
}这个类比较简单，view保存我们设置的view，type用来保存我们view的type信息，可以通过type信息识别我们的header和footer。
public void addHeader(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_HEADER_TYPE_BASE + mHeaders.size();
mHeaders.add(info);
}
public void addFooter(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_FOOTER_TYPE_BASE + mFooters.size();
mFooters.add(info);
}可以看到，每次addHeader或者是addFooter的时候,都通过一个唯一的type信息来区别这个view。
@Override
public long getItemId(int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adjPosition = position - headerCount;
return mAdapter.getItemId(adjPosition);
}
return RECYCLER_HEADER_FOOTER_ID;
}我们需要重新getItemId（）方法，如果是header或者是footer的话，直接返回我们定义的特殊值 RECYCLER_HEADER_FOOTER_ID。如果是adapter中的数据则返回adapter中的相同方法。
@Override
public int getItemViewType(int position) {
if (mAdapter == null) {
throw new IllegalStateException("must have a adapter");
}
int headerCount = getHeaderSize();
int adapterCount = mAdapter.getItemCount();
if (position < headerCount) {
return mHeaders.get(position).type;
} else if (position >= (headerCount + adapterCount)) {
return mFooters.get(position - headerCount - adapterCount).type;
} else {
int adjPosition = position - headerCount;
return mAdapter.getItemViewType(adjPosition);
}
} getItemViewType()是我们必须重写的方法，在这个方法中，我们会标识每一个Header和Footer的viewType。
@Override
public HeaderViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
int delta = viewType - RECYCLER_HEADER_TYPE_BASE;
View view = mHeaders.get(delta).view;
return new HeaderViewHolder(view);
}
if (isFooterView(viewType)) {
int delta = viewType - RECYCLER_FOOTER_TYPE_BASE;
View view = mFooters.get(delta).view;
return new HeaderViewHolder(view);
}
return (HeaderViewHolder) mAdapter.onCreateViewHolder(parent,viewType);
}
@Override
public void onBindViewHolder(HeaderViewHolder holder, int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adapterCount = mAdapter.getItemCount();
int adjPosition = position - headerCount;
if (adjPosition >= 0 && adjPosition < adapterCount) {
mAdapter.onBindViewHolder(holder, adjPosition);
}
}
}最主要的地方来了，在onCreateViewHolder中，我们需要判断当前的viewType是header的还是footer的，如果是header的或者footer的，我们需要算出这个viewtype所对应的view，用这个view来返回HeaderViewHolder。而在onBindViewHolder()方法中，我们只需要定位到属于adapter中的数据就好，然后返回对应的方法即可。完整的代码如下：
package com.gearmotion.app.mylibrary;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;
import java.util.ArrayList;
import java.util.List;
/**
* Created by Charles on 2016/3/21.
*/
public class HeaderRecyclerViewAdapter extends RecyclerView.Adapter<HeaderRecyclerViewAdapter
.HeaderViewHolder> {
//header view type的开始值
private final int RECYCLER_HEADER_TYPE_BASE = 0xff11;
//footer view type的开始值
private final int RECYCLER_FOOTER_TYPE_BASE = 0xff22;
//header和footer的id值
private final int RECYCLER_HEADER_FOOTER_ID = -1;
//用来存放所有的header view的信息
private List<FixedInfo> mHeaders = new ArrayList<>();
//用来存放所有的footer view的信息
private List<FixedInfo> mFooters = new ArrayList<>();
//保存使用默认的RecyclerView.Adapter创建的adapter的值，这个值必须获取到
private RecyclerView.Adapter mAdapter = null;
public HeaderRecyclerViewAdapter() {
}
public HeaderRecyclerViewAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
public void setAdapter(RecyclerView.Adapter adapter) {
this.mAdapter = adapter;
}
@Override
public HeaderViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
int delta = viewType - RECYCLER_HEADER_TYPE_BASE;
View view = mHeaders.get(delta).view;
return new HeaderViewHolder(view);
}
if (isFooterView(viewType)) {
int delta = viewType - RECYCLER_FOOTER_TYPE_BASE;
View view = mFooters.get(delta).view;
return new HeaderViewHolder(view);
}
return (HeaderViewHolder) mAdapter.onCreateViewHolder(parent,viewType);
}
@Override
public void onBindViewHolder(HeaderViewHolder holder, int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adapterCount = mAdapter.getItemCount();
int adjPosition = position - headerCount;
if (adjPosition >= 0 && adjPosition < adapterCount) {
mAdapter.onBindViewHolder(holder, adjPosition);
}
}
}
@Override
public int getItemCount() {
if (mAdapter != null) {
return mHeaders.size() + mAdapter.getItemCount() + mFooters.size();
} else {
return mHeaders.size() + mFooters.size();
}
}
@Override
public int getItemViewType(int position) {
if (mAdapter == null) {
throw new IllegalStateException("must have a adapter");
}
int headerCount = getHeaderSize();
int adapterCount = mAdapter.getItemCount();
if (position < headerCount) {
return mHeaders.get(position).type;
} else if (position >= (headerCount + adapterCount)) {
return mFooters.get(position - headerCount - adapterCount).type;
} else {
int adjPosition = position - headerCount;
return mAdapter.getItemViewType(adjPosition);
}
}
@Override
public long getItemId(int position) {
int headerCount = getHeaderSize();
if (mAdapter != null && position >= headerCount) {
int adjPosition = position - headerCount;
return mAdapter.getItemId(adjPosition);
}
return RECYCLER_HEADER_FOOTER_ID;
}
public void addHeader(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_HEADER_TYPE_BASE + mHeaders.size();
mHeaders.add(info);
}
public void addFooter(View view) {
FixedInfo info = new FixedInfo();
info.view = view;
info.type = RECYCLER_FOOTER_TYPE_BASE + mFooters.size();
mFooters.add(info);
}
public int getHeaderSize() {
return mHeaders.size();
}
public int getFooterSize() {
return mFooters.size();
}
private boolean isHeaderView(int type) {
int delta = type - RECYCLER_HEADER_TYPE_BASE;
return delta >= 0 && delta < mHeaders.size();
}
private boolean isFooterView(int type) {
int delta = type - RECYCLER_FOOTER_TYPE_BASE;
return delta >= 0 && delta < mFooters.size();
}
//用来保存footer和headers的信息
private class FixedInfo {
public View view;
public int type;
}
//自定义的viewholder
public static class HeaderViewHolder extends RecyclerView.ViewHolder {
public HeaderViewHolder(android.view.View itemView) {
super(itemView);
}
}
}最后我们在使用的时候将原始创建的adapter传递给HeaderRecyclerViewAdapter即可。
package com.gearmotion.app.headerrecyclerviewmotion;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.text.Layout;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.gearmotion.app.mylibrary.HeaderRecyclerViewAdapter;
public class MainActivity extends AppCompatActivity {
private RecyclerView mRecyclerView;
private LayoutInflater mInflater;
private String[] mDatas = new String[]{"title1", "title2", "title3", "title4", "title5",
"title6"};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mInflater = LayoutInflater.from(this);
mRecyclerView = (RecyclerView) this.findViewById(R.id.recyclerview);
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
CustomAdapter tmpAdapter = new CustomAdapter();
HeaderRecyclerViewAdapter mAdapter = new HeaderRecyclerViewAdapter(tmpAdapter);
mAdapter.addHeader(createView("head1"));
mAdapter.addHeader(createView("head2"));
mAdapter.addHeader(createView("head3"));
mAdapter.addFooter(createView("foot1"));
mAdapter.addFooter(createView("foot2"));
mAdapter.addFooter(createView("foot3"));
mRecyclerView.setAdapter(mAdapter);
}
private View createView(String title) {
TextView tv = new TextView(this);
tv.setText(title);
tv.setLayoutParams(new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
70));
tv.setGravity(Gravity.CENTER);
return tv;
}
public class CustomAdapter extends RecyclerView.Adapter<CustomViewHolder> {
@Override
public CustomViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View root = mInflater.inflate(R.layout.item, null);
return new CustomViewHolder(root);
}
@Override
public void onBindViewHolder(CustomViewHolder holder, int position) {
holder.textView.setText(mDatas[position]);
}
@Override
public int getItemCount() {
return mDatas.length;
}
}
public class CustomViewHolder extends HeaderRecyclerViewAdapter.HeaderViewHolder {
public TextView textView;
public CustomViewHolder(View itemView) {
super(itemView);
textView = (TextView) itemView.findViewById(R.id.itemtextview);
}
}
}结果如下：
代码地址如下：https://github.com/summerpxy/HeaderRecyclerViewAdapter.git
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