Recyclerview --- （一）简单的使用

【记录】记录点滴

【需求】从最简单的RecyclerView使用开始记录

RecyclerView和ListView的使用非常相似：1. 导入包；2. 创建Adapter；3. 设置RecyclerView

1. 导入support-v7包，例如

implementation 'com.android.support:recyclerview-v7:27.1.1'

2. 继承RecyclerView.Adater，实现自定义的Adapter

public class SimpleDemoAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    List<String> data;

    public SimpleDemoAdapter (List<String> data) {
        this.data = data;
    }

    /**
     * 渲染视图，返回ViewHolder
     */
    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //使用系统布局，里面只有一个TextView
        View v = LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
        TypeOne vh = new TypeOne(v);
        return vh;
    }

    /**
     * 绑定数据，设置Item内容的地方
     */
    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        ((TypeOne)holder).tvContent.setText("position = " + position);
    }

    /**
     * 返回数据长度
     */
    @Override
    public int getItemCount() {
        return data == null ? 0 : data.size();
    }

    /**
     * 自定义ViewHolder，后续会记录多类型Item的实现，所以命名就叫TypeOne
     */
    class TypeOne extends RecyclerView.ViewHolder{
        public TextView tvContent;
        public TypeOne(View itemView) {
            super(itemView);
            tvContent = itemView.findViewById(android.R.id.text1);
        }
    }
}

 3. 设置RecyclerView

在Activity或者Fragment等中

adapter = new SimpleDemoAdapter(data);

//以LinearLayoutManager示例，默认垂直方向
//也可以使用new LinearLayoutManager(context, LinearLayoutManager.VERTICAL, false);来指定方向
LinearLayoutManager llm = new LinearLayoutManager(context);
rv.setLayoutManager(llm);
rv.setAdapter(adapter);

PS：多种类型 Item 时，需要重写 getItemViewType()

1）先设计一个类，其中的 type 对应 Item 的类型

public class MultiTypeRvBean {

    public int type = 0;
    public String content;

    public MultiTypeRvBean(int type, String content) {
        this.type = type;
        this.content = content;
    }
}

 2）重写Adapter中的 getItemViewType

    //这里简单些，直接返回MultiType中的type，并依据type判断
    @Override
    public int getItemViewType(int position) {
        MultiTypeRvBean bean = data.get(position);
        return bean.type;
    }

3）修改onCreateViewHolder与onBindViewHolder

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = null;
        RecyclerView.ViewHolder vh;
        switch (viewType){
            case 0:
                v = LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
                vh = new TypeOne(v);
                return vh;
            case 1:
                v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_tv_center, parent, false);
                vh = new TypeTwo(v);
                return vh;
            case 2:
            default:
                v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_tv_right, parent, false);
                vh = new TypeThree(v);
                return vh;
        }

    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {

        switch (getItemViewType(position)){
            case 0:
                ((TypeOne)holder).tvContent.setText("样式一");
                break;
            case 1:
                ((TypeTwo)holder).tvCenter.setText("样式二");
                break;
            case 2:
            default:
                ((TypeThree)holder).tvRight.setText("样式三");
        }
    }

PS：嵌套使用RecyclerView，和普通使用一样

    /**
     * 重点在这里，0：渲染嵌套的Grid，只含有一个RecyclerView，1：渲染普通的Item，只含有一个TextView
     */
    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = null;
        RecyclerView.ViewHolder vh;
        switch (viewType) {
            case 0:
                v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_nest_recycler, parent, false);
                vh = new TypeNestRecycler(v);
                return vh;
            case 1:
            default:
                v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_tv_normal, parent, false);
                vh = new TypeNormal(v);
                return vh;

        }

    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {

        switch (getItemViewType(position)) {
            case 0:
                GridLayoutManager glm = new GridLayoutManager(context, 3, GridLayoutManager.HORIZONTAL, false);
                SimpleGridAdapter adapter = new SimpleGridAdapter(gridData);
                ((TypeNestRecycler) holder).nestGridRv.setLayoutManager(glm);
                ((TypeNestRecycler) holder).nestGridRv.setAdapter(adapter);
                break;
            case 1:
                ((TypeNormal) holder).tvContent.setText("样式一");
                break;
        }
    }

    /**
     * 只返回两种类型，0 嵌套的RecyclerView，1 简单的TextView
     */
    @Override
    public int getItemViewType(int position) {
        MultiTypeRvBean bean = data.get(position);
        return bean.type;
    }

 嵌套的RecyclerView的布局也非常简单item_nest_recycler.xml

<!-- item_nest_recycler.xml -->
<?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="200dp">
    <android.support.v7.widget.RecyclerView
        android:id="@+id/nest_grid_recycler"
        android:layout_width="match_parent"
        android:layout_height="200dp">
    </android.support.v7.widget.RecyclerView>
</LinearLayout>

顺便记录下方法，返回当前 item 的跨度大小，就是占用了几行（几列），套用别人博客的图，可以实现圈出的 item 效果，这个 item 占用了2列（https://www.jianshu.com/p/675883c26ef2）

//合并Grid中列(行)
setSpanSizeLookup