简介
RecyclerView是我们开发过程中经常使用到的一个元素，原生的RecyclerView.Adapter基本上可以满足一般的需求，关于RecyclerView的基础介绍请移步：
RecyclerView基础使用
关于多类型的Item,原生的Adapter可以通过getItemViewType返回对应的ViewHolder类型，然后在onCreateViewHolder传入的type参数，生成不同的ViewHolder，更要命的是数据绑定过程中onBindViewHolder只传入ViewHolder对象和position，针对不同的ViewHolder，我们只能通过instanceof和强制类型装换来对不同的ViewHolder进行不同的数据操作。
这样做的弊端就是，后续如果需要添加一个类型，几乎需要修改Adapter类中的每一个方法，不利于维护。
类结构
目的
- 便于维护。增删Item的类型不需要修改Adapter的代码；
- 条例清晰。不同类型的Item对应不同的Bean类，对应不用的ViewHolder,对应不同的layout, item type <-> layout <—> ViewHolder <-> java bean
- 工厂接口。抽象出TypeFactory接口，针对同一个Bean,可以使用不同的layout和不同的ViewHolder。
思路
- 所有Bean类实现统一Visitable接口，实现type方法，返回对应的layout id;
- 创建BaseViewHolder使用泛型，T为Bean类。使用SparseArray存储View,View的id作为唯一标识。
- 具体的ViewHolder类，继承BaseViewHolder,传入不同的Bean类，方便不同的ViewHolder中绑定不同的数据。
- Adapter实现中使用Visitable List同一处理列表数据，使用事项TypeFactory接口的实例返回ItemType，viewHolder等
代码结构
代码内容
Visitable接口
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| public interface Visitable {
int type(TypeFactory typeFactory);
}
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TypeFactory接口
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| public interface TypeFactory {
int type(BannerBean bannerBean);
int type(ContentBean contentBean);
int type(SearchBean searchBean);
int type(DividerBean dividerBean);
BaseViewHolder createViewHolder(int type, View itemView);
}
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BaseViewHolder抽象类
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| public abstract class BaseViewHolder<T> extends RecyclerView.ViewHolder{
SparseArray<View> mViews;
View mItemView;
public BaseViewHolder(View itemView) {
super(itemView);
mItemView = itemView;
mViews = new SparseArray<>();
}
public View getView(int resId) {
View view = mViews.get(resId);
if(view== null) {
view = mItemView.findViewById(resId);
mViews.put(resId, view);
}
return view;
}
public abstract void bindViewData(T data);
}
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TypeFactory实现类: ItemTypeFactory
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| public class ItemTypeFactory implements TypeFactory {
public static final int BANNER_ITEM_LAYOUT = R.layout.rv_item_banner;
public static final int CONTENT_ITEM_LAYOUT = R.layout.rv_item_content;
public static final int SEARCH_ITEM_LAYOUT = R.layout.rv_item_search;
public static final int DIVIDER_ITEM_LAYOUT = R.layout.rv_item_divider;
@Override
public int type(BannerBean bannerBean) {
return BANNER_ITEM_LAYOUT;
}
@Override
public int type(ContentBean contentBean) {
return CONTENT_ITEM_LAYOUT;
}
@Override
public int type(DividerBean dividerBean){
return DIVIDER_ITEM_LAYOUT;
}
@Override
public int type(SearchBean dividerBean){
return SEARCH_ITEM_LAYOUT;
}
@Override
public BaseViewHolder createViewHolder(int type, View itemView) {
switch (type) {
case BANNER_ITEM_LAYOUT:
return new BannerViewHolder(itemView);
case SEARCH_ITEM_LAYOUT:
return new SearchViewHolder(itemView);
case CONTENT_ITEM_LAYOUT:
return new ContentViewHolder(itemView);
case DIVIDER_ITEM_LAYOUT:
return new DividerViewHolder(itemView);
default:
return null;
}
}
}
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各种Java Bean类
BannerBean
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| public class BannerBean implements Visitable {
int[] mResIds;
public BannerBean(int[] mResIds) {
this.mResIds = mResIds;
}
public int[] getmResIds() {
return mResIds;
}
public void setmResIds(int[] mResIds) {
this.mResIds = mResIds;
}
@Override
public int type(TypeFactory typeFactory) {
return typeFactory.type(this);
}
}
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| <?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="200dp">
<cn.bingoogolapple.bgabanner.BGABanner
android:id="@+id/bgabanner_header"
android:layout_width="match_parent"
android:layout_height="200dp">
</cn.bingoogolapple.bgabanner.BGABanner>
</LinearLayout>
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ContentBean
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| public class ContentBean implements Visitable{
String content;
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public ContentBean(String content) {
this.content = content;
}
@Override
public int type(TypeFactory typeFactory) {
return typeFactory.type(this);
}
}
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| <?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="wrap_content">
<TextView
android:id="@+id/tv_content"
android:textStyle="italic"
android:fontFamily="sans-serif-condensed"
android:textSize="16sp"
android:gravity="center_horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
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DividerBean
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| public class DividerBean implements Visitable{
@Override
public int type(TypeFactory typeFactory) {
return typeFactory.type(this);
}
}
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| <?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="wrap_content"
android:background="@drawable/divider">
</LinearLayout>
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SearchBean
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| public class SearchBean implements Visitable {
@Override
public int type(TypeFactory typeFactory) {
return typeFactory.type(this);
}
}
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| <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal" android:layout_width="match_parent"
android:layout_height="50dp"
android:padding="6dp">
<EditText
android:layout_marginLeft="30dp"
android:id="@+id/et_search"
android:layout_width="0dp"
android:layout_weight="9"
android:maxLines="1"
android:textSize="10sp"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:hint="输入文字搜索..."
android:background="@drawable/bg_search"
android:layout_height="match_parent" />
<ImageView
android:id="@+id/bt_search"
android:layout_width="0dp"
android:layout_weight="2"
android:src="@drawable/search"
android:layout_height="match_parent" />
</LinearLayout>
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MultiRecyclerAdapter
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| public class MultiRecyclerAdapter extends RecyclerView.Adapter<BaseViewHolder> {
List<Visitable> mData;
TypeFactory typeFactory;
public MultiRecyclerAdapter(List<Visitable> mData) {
this.mData = mData;
this.typeFactory = new ItemTypeFactory();
}
@Override
public BaseViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(viewType, parent, false);
return typeFactory.createViewHolder(viewType, view);
}
@Override
public void onBindViewHolder(BaseViewHolder holder, int position) {
holder.bindViewData(mData.get(position));
}
@Override
public int getItemViewType(int position) {
return mData.get(position).type(typeFactory);
}
@Override
public int getItemCount() {
return (mData != null ? mData.size() : 0);
}
}
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示例
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| public class MultiActivity extends AppCompatActivity {
@BindView(R.id.rv_content)
RecyclerView rvContent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_weather);
ButterKnife.bind(this);
List<Visitable> beans = new ArrayList<>();
int[] resIds = {R.mipmap.banner_one, R.mipmap.banner_two, R.mipmap.banner_three, R.mipmap.banner_four, R.mipmap.banner_five};
beans.add(new BannerBean(resIds));
beans.add(new SearchBean());
beans.add(new DividerBean());
beans.add(new ContentBean("one"));
beans.add(new ContentBean("one"));
beans.add(new ContentBean("one"));
beans.add(new DividerBean());
beans.add(new ContentBean("two"));
beans.add(new ContentBean("two"));
beans.add(new ContentBean("two"));
beans.add(new DividerBean());
beans.add(new ContentBean("three"));
beans.add(new ContentBean("three"));
beans.add(new ContentBean("three"));
beans.add(new DividerBean());
beans.add(new ContentBean("four"));
beans.add(new ContentBean("four"));
beans.add(new ContentBean("four"));
beans.add(new DividerBean());
MultiRecyclerAdapter multiRecyclerAdapter = new MultiRecyclerAdapter(beans);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false);
rvContent.setAdapter(multiRecyclerAdapter);
rvContent.setLayoutManager(linearLayoutManager);
}
}
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效果
写在最后
思路来源：
https://medium.com/@dpreussler/writing-better-adapters-1b09758407d2
github上也有很多开源的万能Adapter，但是个人感觉这个思路虽然实现上代码会相对较多，但是层次分析，便于维护，扩展性较好。想要添加一个新类型的ItemType，只需要稍作修改即可快速完成，不用修改Adapter的代码。
