一、引入和使用控件

1. 引入

RecyclerView属于新增控件，定义在AndroidX中，需要在app/build.gradle文件中dependencies闭包中引入：

dependencies {
    
    implementation 'androidx.recyclerview:recyclerview:1.1.0'

}

2. 使用

在布局文件.xml中使用：

<?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="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/messageRecyclerView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        />

</LinearLayout>

二、布局方式

1. LinearLayoutManager 线性布局

竖向滚动

val layoutManager = LinearLayoutManager(this)
messageRecyclerView.layoutManager = layoutManager

adapter = MsgAdapter(msgList)
messageRecyclerView.adapter = adapter

横向滚动

val layoutManager = LinearLayoutManager(this)
layoutManager.orientation = LinearLayoutManager.HORIZONTAL
messageRecyclerView.layoutManager = layoutManager

adapter = MsgAdapter(msgList)
messageRecyclerView.adapter = adapter

2. GridLayoutManager 网格布局

val layoutManager = GridLayoutManager(this, 6)
messageRecyclerView.layoutManager = layoutManager

adapter = MsgAdapter(msgList)
messageRecyclerView.adapter = adapter

3. StaggeredGridLayoutManager 瀑布布局

val layoutManager = StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL)
messageRecyclerView.layoutManager = layoutManager

adapter = MsgAdapter(msgList)
messageRecyclerView.adapter = adapter

三、适配器

class MsgAdapter(val msgList: List<Msg>): RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    inner class LeftViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        val leftMsg: TextView = view.findViewById(R.id.leftMsg)   // 加载控件
    }

    inner class RightViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        val rightMsg: TextView = view.findViewById(R.id.rightMsg)  // 加载控件
    }

    override fun getItemViewType(position: Int): Int {
        // 返回当前子项对应的布局类型
        val msg = msgList[position]
        return msg.type
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        if (viewType == Msg.TYPE_RECEIVED) {   //加载布局，创建Holder实例后加载控件
            val view =
                LayoutInflater.from(parent.context).inflate(R.layout.msg_left_item, parent, false)
            // 加载完控件后可在此完成点击事件等
            return LeftViewHolder(view)
        } else {
            val view =
                LayoutInflater.from(parent.context).inflate(R.layout.msg_right_item, parent, false)
            return RightViewHolder(view)
        }

    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        // 在此处给Holder里的控件绑定值
        val msg = msgList[position]
        when (holder) {
            is LeftViewHolder -> holder.leftMsg.text = msg.content
            is RightViewHolder -> holder.rightMsg.text = msg.content
            else -> throw IllegalArgumentException()
        }
    }
    // 获取子项总数
    override fun getItemCount(): Int = msgList.size
}

四、RecyclerView的点击事件

在onCreatViewHolder()中创建

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
    val view = LayoutInflater.from(parent.context).inflate(R.layout.fruit_item, parent, false)
    val viewHolder = ViewHolder(view)
    viewHolder.itemView.setOnClickListener{
        val position = viewHolder.adapterPosition
        val fruit = fruitList[position]
        Toast.makeText(parent.context, "click view ${fruit.name}", Toast.LENGTH_SHORT).show()
        }
    viewHolder.fruitImage.setOnClickListener{
        val position = viewHolder.adapterPosition
        val fruit = fruitList[position]
        Toast.makeText(parent.context, "click view ${fruit.imageId}", Toast.LENGTH_SHORT).show()
        }
    return viewHolder
    }