一、添加recyclerview依赖库之后，编辑xml文件：

<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/chatrecyclerview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_weight="1"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:id="@+id/etcontent"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"/>
        <Button
            android:id="@+id/btnsend"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="发送"/>
    </LinearLayout>
</LinearLayout>

二、定义消息的实体类，定义常量的关键字const，只有在单例类、companion object或者顶层方法中才可以使用

class MsgDatas(val msg:String,val type:Int ) {
    companion object{
        const val SENTMSG:Int=0
        const val RECEIVERMSG:Int=1
    }
}

三、Recyclerview的子布局
left

<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent"
    android:layout_height="wrap_content">
<TextView
    android:layout_width="wrap_content"
    android:layout_gravity="left"
    android:layout_height="wrap_content"
    android:textColor="#03A9F4"
    android:id="@+id/tvleftitem"/>
</FrameLayout>

right

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <TextView
        android:layout_width="wrap_content"
        android:layout_gravity="right"
        android:layout_height="wrap_content"
        android:textColor="#FF9800"
        android:id="@+id/tvrightitem"/>

</FrameLayout>

四、Recyclerview的适配器：

class ChatAdapter(val msgList: List<MsgDatas>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    inner class LeftChatViewHolder(view: View): RecyclerView.ViewHolder(view) {
        val textLeft:TextView=view.findViewById(R.id.tvleftitem)
    }
    inner class RightChatViewHolder(view: View): RecyclerView.ViewHolder(view) {
        val textRight:TextView=view.findViewById(R.id.tvrightitem)
    }

    override fun onCreateViewHolder(p0: ViewGroup, p1: Int): RecyclerView.ViewHolder {
        if (p1==MsgDatas.SENTMSG){
            val view=LayoutInflater.from(p0.context).inflate(R.layout.msg_left_item,p0,false)

         return   LeftChatViewHolder(view)
        }else{
            val viewRight=LayoutInflater.from(p0.context).inflate(R.layout.msg_right_item,p0,false)
            return RightChatViewHolder(viewRight)
        }
    }

    override fun getItemCount(): Int {
     return  msgList.size
    }

    override fun onBindViewHolder(p0: RecyclerView.ViewHolder, p1: Int) {
       val msg=msgList[p1]
        when(p0){
           is LeftChatViewHolder->{
               p0.textLeft.setText(msg.msg)
           }
            is RightChatViewHolder ->{
                p0.textRight.setText(msg.msg)
            }
            else -> throw IllegalArgumentException()
        }
    }

    override fun getItemViewType(position: Int): Int {
        val msg=msgList[position]
        return msg.type
    }
}

适配器根据不同的viewType创建不同的界面，getItemViewType方法返回当前position对应的消息类型
五、activity中的代码：

class ChatActivity:AppCompatActivity(),View.OnClickListener{
   private val msgList=ArrayList<MsgDatas>()
   private var adaper:ChatAdapter?=null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.chat_layout)

        initData()
        btnsend.setOnClickListener(this)

        val layMannger= LinearLayoutManager(this)
        chatrecyclerview.layoutManager=layMannger

        adaper =ChatAdapter(msgList)
        chatrecyclerview.adapter=adaper

    }

    override fun onClick(v: View?) {
        when(v){
            btnsend ->{
                val content=etcontent.text.toString()
                if (content.isNotEmpty()){
                    val msg=MsgDatas(content,MsgDatas.SENTMSG)
                    msgList.add(msg)

                    adaper?.notifyItemInserted(msgList.size-1)
                    etcontent.setText("")
                }
            }
        }
    }

    private fun initData(){
        val msg1=MsgDatas("hello,who are you",MsgDatas.SENTMSG)
        msgList.add(msg1)

        val msg2=MsgDatas("hello,who are you",MsgDatas.RECEIVERMSG)
        msgList.add(msg2)

        val msg3=MsgDatas("hello,who are you",MsgDatas.SENTMSG)
        msgList.add(msg3)
    }

}

如果想要好看的聊天背景，可以添加.9图片，此外这里调用适配器的notifyItemInserted()方法用于通知列表有新的数据插入，这样新增的数据才能在recyclerview中展现处理。你也可以调用适配器的notify DATaSetChanged()方法，将recyclerview中的所有元素刷新一次，这样不管是增加、删除还是修改元素，界面都会显示最新元素，缺点是效率低一些，如果数据多的情况，可以调用scrolltoposition()方法将显示的数据定位到最后一行，以保证一定能看到最后发的消息