Android:RecyclerView 添加 Header 和 Footer(一)
一、简介
与 ListView 和 GridView 相比,RecyclerView 的灵活性和性能上的都有很大的提升。所以用 RecyclerView 来实现 Header 和 Footer 更加灵活方便。
二、实现
1.布局
列表
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.study.wnw.recyclerviewheaderfooter.MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</RelativeLayout>
列表项(item)
<?xml version="1.0" encoding="utf-8"?><LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="50dp">
<TextView
android:id="@+id/item"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:textSize="20sp"
android:textColor="@color/colorAccent"
android:gravity="center"
android:background="#08e630"/>
</LinearLayout>
Header
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="100dp">
<TextView
android:id="@+id/header"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="我是Header"
android:textSize="30sp"
android:textColor="#fde70b0b"
android:background="#f9777979"
android:gravity="center"/>
</LinearLayout>
Footer
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="100dp">
<TextView
android:id="@+id/footer"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="我是Footer"
android:textSize="30sp"
android:textColor="#fde70b0b"
android:background="#f9777979"
android:gravity="center"/>
</LinearLayout>
2.代码实现
MainActivity.java
public class MainActivity extends Activity {
private RecyclerView mRecyclerView;
private MyAdapter mMyAdapter;
private List<String> mList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//RecyclerView三部曲+LayoutManager
mRecyclerView = (RecyclerView)findViewById(R.id.recyclerview);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(linearLayoutManager);
initData();
mMyAdapter = new MyAdapter(mList);
mRecyclerView.setAdapter(mMyAdapter);
//为RecyclerView添加HeaderView和FooterView
setHeaderView(mRecyclerView);
setFooterView(mRecyclerView);
}
//初始化RecyclerView中每个item的数据
private void initData(){
mList = new ArrayList<String>();
for (int i = 0; i < 20; i++){
mList.add("item" + i);
}
}
private void setHeaderView(RecyclerView view){
View header = LayoutInflater.from(this).inflate(R.layout.header, view, false);
mMyAdapter.setHeaderView(header);
}
private void setFooterView(RecyclerView view){
View footer = LayoutInflater.from(this).inflate(R.layout.footer, view, false);
mMyAdapter.setFooterView(footer);
}
}
MyAdapter.java
public class MyAdapter extendsRecyclerView.Adapter<RecyclerView.ViewHolder> {
public static final int TYPE_HEADER = 0; //说明是带有Header的
public static final int TYPE_FOOTER = 1; //说明是带有Footer的
public static final int TYPE_NORMAL = 2; //说明是不带有header和footer的
//获取从Activity中传递过来每个item的数据集合
private List<String> mDatas;
//HeaderView, FooterView
private View mHeaderView;
private View mFooterView;
//构造函数
public MyAdapter(List<String> list){
this.mDatas = list;
}
//HeaderView和FooterView的get和set函数
public View getHeaderView() {
return mHeaderView;
}
public void setHeaderView(View headerView) {
mHeaderView = headerView;
notifyItemInserted(0);
}
public View getFooterView() {
return mFooterView;
}
public void setFooterView(View footerView) {
mFooterView = footerView;
notifyItemInserted(getItemCount()-1);
}
/** 重写这个方法,很重要,是加入Header和Footer的关键,我们通过判断item的类型,从而绑定不同的view * */
@Override
public int getItemViewType(int position) {
if (mHeaderView == null && mFooterView == null){
return TYPE_NORMAL;
}
if (position == 0){
//第一个item应该加载Header
return TYPE_HEADER;
}
if (position == getItemCount()-1){
//最后一个,应该加载Footer
return TYPE_FOOTER;
}
return TYPE_NORMAL;
}
//创建View,如果是HeaderView或者是FooterView,直接在Holder中返回
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if(mHeaderView != null && viewType == TYPE_HEADER) {
return new ListHolder(mHeaderView);
}
if(mFooterView != null && viewType == TYPE_FOOTER){
return new ListHolder(mFooterView);
}
View layout = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
return new ListHolder(layout);
}
//绑定View,这里是根据返回的这个position的类型,从而进行绑定的, HeaderView和FooterView, 就不同绑定了
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
if(getItemViewType(position) == TYPE_NORMAL){
if(holder instanceof ListHolder) {
//这里加载数据的时候要注意,是从position-1开始,因为position==0已经被header占用了
((ListHolder) holder).tv.setText(mDatas.get(position-1));
return;
}
return;
}else if(getItemViewType(position) == TYPE_HEADER){
return;
}else{
return;
}
}
//在这里面加载ListView中的每个item的布局
class ListHolder extends RecyclerView.ViewHolder{
TextView tv;
public ListHolder(View itemView) {
super(itemView);
//如果是headerview或者是footerview,直接返回
if (itemView == mHeaderView){
return;
}
if (itemView == mFooterView){
return;
}
tv = (TextView)itemView.findViewById(R.id.item);
}
}
//返回View中Item的个数,这个时候,总的个数应该是ListView中Item的个数加上HeaderView和FooterView
@Override
public int getItemCount() {
if(mHeaderView == null && mFooterView == null){
return mDatas.size();
}else if(mHeaderView == null && mFooterView != null){
return mDatas.size() + 1;
}else if (mHeaderView != null && mFooterView == null){
return mDatas.size() + 1;
}else {
return mDatas.size() + 2;
}
}
}
三、总结
实现 Header 和 Footer 的方式很多,这是一种方法。所有的实现方法都需要通过 Adapter 来实现,只需要控制好数据列表中 position 就可以了。这里仅仅显示文字,当然还可以实现其他更复杂的布局。