Android RecycleView多种布局实现（工厂模式）

RecycleView是个很常用的控件，很多APP中都可以看到它的身影，同时它也是个很难用的控件，主要就难在多种布局的实现。

在《第一行代码—Android》这本书里边有个RecycleView实现的聊天界面布局，左右两种布局写在了同一个文件中，如果是发送来的消息，就隐藏右侧布局，反之隐藏左侧布局，这种方式对于比较简单的、只有两种Item的界面是可行的，假如我们的Item有多种布局，那么这种方式就显得很笨重。对于多种布局，我们可以使用工厂模式来实现。

Github:https://github.com/imcloudfloating/DesignApp

1.首先看看效果（GIF一直上传失败，只好传JPG了）：

这里的LayoutManager使用GridLayoutManager，设置为6列，然后在Adapter类中根据不同的类型来设置所占列数，具体见Adapter类的setSpanCount方法。

2.然后是类图：

3.Adapter类：

适配器的代码很短，设置数据和绑定View的代码都写在了ItemHolder的子类里面；

List<Item>储存三种类型的Item数据，如果需要增加新的类型，只要实现Item接口就可以了；

在onBindViewHolder方法中调用ItemHolder的setData()方法来设置数据；

 public class MultiListAdapter extends RecyclerView.Adapter<ItemHolder> {

     private List<Item> mDataList;

     public MultiListAdapter(List<Item> dataList) {
         mDataList = dataList;
     }

     @NonNull
     @Override
     public ItemHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int type) {
         return ItemHolderFactory.getItemHolder(viewGroup, type);
     }

     @Override
     public void onBindViewHolder(@NonNull ItemHolder viewHolder, int i) {
         //设置 Holder 数据
         viewHolder.setData(mDataList.get(i));
     }

     @Override
     public int getItemViewType(int position) {
         return mDataList.get(position).getType();
     }

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

     public void setSpanCount(GridLayoutManager layoutManager) {
         layoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
             @Override
             public int getSpanSize(int i) {
                 int type = getItemViewType(i);
                 switch (type) {
                     default:
                     case ItemHolderFactory.ITEM_LARGE:
                         return 3;
                     case ItemHolderFactory.ITEM_SMALL:
                         return 2;
                     case ItemHolderFactory.ITEM_TITLE_BAR:
                         return 6;
                 }
             }
         });
     }
 }

4.ItemHolder抽象类：

setData方法用来设置Item布局的数据

 public abstract class ItemHolder extends RecyclerView.ViewHolder {
     public ItemHolder(View item) {
         super(item);
     }

     public abstract void setData(Item itemData);
 }

5.LargeItemHolder类：

另外两个类似

 public class LargeItemHolder extends ItemHolder {

     private ImageView mItemImage;
     private TextView mTitle;
     private TextView mSubTitle;

     public LargeItemHolder(View item) {
         super(item);
         mItemImage = item.findViewById(R.id.item_image);
         mTitle = item.findViewById(R.id.item_title);
         mSubTitle = item.findViewById(R.id.item_sub_title);
     }

     @Override
     public void setData(Item itemData) {
         ItemLarge item = (ItemLarge) itemData;
         mItemImage.setImageBitmap(item.getImage());
         mTitle.setText(item.getTitle());
         mSubTitle.setText(item.getSubTitle());
     }
 }

6.Item接口：

 public interface Item {
     int getType();
 }

7.ItemLarge类（一个图片、一个标题和一个副标题）：

另外两个类似

 public class ItemLarge implements Item {

     private Bitmap mImage;
     private String mTitle;
     private String mSubTitle;

     public ItemLarge(Bitmap bitmap, String title, String subTitle) {
         mImage = bitmap;
         mTitle = title;
         mSubTitle = subTitle;
     }

     public Bitmap getImage() {
         return mImage;
     }

     public String getTitle() {
         return mTitle;
     }

     public String getSubTitle() {
         return mSubTitle;
     }

     @Override
     public int getType() {
         return ItemHolderFactory.ITEM_LARGE;
     }
 }

8.工厂类ItemHolderFactory：

三个常量表示不同的布局类型，通过getItemHolder来创建ViewHolder。

 public class ItemHolderFactory {

     public static final int ITEM_LARGE = 0;
     public static final int ITEM_SMALL = 1;
     public static final int ITEM_TITLE_BAR = 2;

     @IntDef({
             ITEM_LARGE,
             ITEM_SMALL,
             ITEM_TITLE_BAR
     })
     @interface ItemType {}

     static ItemHolder getItemHolder(ViewGroup parent, @ItemType int type) {
         switch (type) {
             default:
             case ITEM_LARGE:
                 return new LargeItemHolder(LayoutInflater
                         .from(parent.getContext()).inflate(R.layout.item_large, parent, false));
             case ITEM_SMALL:
                 return new SmallItemHolder(LayoutInflater
                         .from(parent.getContext()).inflate(R.layout.item_small, parent, false));
             case ITEM_TITLE_BAR:
                 return new TitleBarItemHolder(LayoutInflater
                         .from(parent.getContext()).inflate(R.layout.item_title_bar, parent, false));
         }
     }
 }

9.ListActivity类：

 public class ListActivity extends AppCompatActivity {

     List<Item> itemList = new ArrayList<>();

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_list);

         initData();

         GridLayoutManager layoutManager = new GridLayoutManager(this, 6);
         MultiListAdapter adapter = new MultiListAdapter(itemList);
         adapter.setSpanCount(layoutManager);

         RecyclerView recyclerView = findViewById(R.id.recycle_view);
         recyclerView.setLayoutManager(layoutManager);
         recyclerView.setAdapter(adapter);
     }

     private void initData() {
         //添加数据
         itemList.add(new ItemTitleBar("Hot New", null));
         itemList.add(new ItemLarge(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_1),
                 "One More Light",
                 "Linkin Park"));
         itemList.add(new ItemLarge(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_2),
                 "Let Go ",
                 "Avril Lavigne"));
         itemList.add(new ItemTitleBar("Recommended", null));
         itemList.add(new ItemSmall(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_3),
                 "Bridge to Terabithia"));
         itemList.add(new ItemSmall(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_4),
                 "Life Is Beautiful"));
         itemList.add(new ItemSmall(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_5),
                 "A Violent Flame"));
         itemList.add(new ItemTitleBar("Top Rated", null));
         itemList.add(new ItemLarge(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_6),
                 "Furious 7: Original Motion Picture Soundtrack",
                 "Various Artists"));
         itemList.add(new ItemLarge(
                 BitmapFactory.decodeResource(getResources(), R.drawable.img_7),
                 "Halo 5: Guardians (Original Soundtrack)",
                 "Kazuma Jinnouchi"));
     }
 }

10.布局文件（item_large.xml）：

layout_width用match_parent是为了Item在网格中居中，此处match_parent相当于宽度为Item所占的列数。

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
     android:orientation="vertical"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:layout_margin="4dp"
     android:background="#ffffff"
     android:elevation="2dp">

     <ImageView
         android:contentDescription="@id/item_title"
         android:id="@+id/item_image"
         android:layout_width="match_parent"
         android:layout_height="170dp"
         android:scaleType="centerCrop"
         tools:src="@drawable/img_7" />

     <TextView
         android:id="@+id/item_title"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginTop="8dp"
         android:paddingStart="8dp"
         android:paddingEnd="8dp"
         android:lines="1"
         android:ellipsize="end"
         android:textColor="#000000"
         android:textSize="18sp"
         tools:text="Item Title" />

     <TextView
         android:id="@+id/item_sub_title"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginBottom="8dp"
         android:paddingStart="8dp"
         android:paddingEnd="8dp"
         android:lines="1"
         android:ellipsize="end"
         android:textSize="14sp"
         tools:text="Sub Title" />

 </LinearLayout>