1. 简易聊天工具

实现一个简易聊天工具需要一个消息列表，一个消息编辑框和消息发送按钮。我们利用RecyclerView控件来显示控件，并实现RecyclerView下拉来加载以往的消息。

我们用ChartMessage记录消息内容，ChatMessageAdapter实现了一个简单的消息界面，一个头像和文本消息。

class ChatMessageAdapter(context: Context) : RecyclerView.Adapter() {private val VIEW_TYPE_HEADER_VIEW = 100private val VIEW_TYPE_CONTENT_VIEW = 200private val mContext: Context = contextprivate val mContent: MutableList = ArrayList()private val mHeaderViewList: ArrayList = ArrayList()override fun getItemViewType(position: Int): Int {return if (position < getHeaderViewSize()) {VIEW_TYPE_HEADER_VIEW + position} else {VIEW_TYPE_CONTENT_VIEW}}override fun onCreateViewHolder(viewGroup: ViewGroup, viewType: Int): ItemViewHolder {return if (viewType == VIEW_TYPE_CONTENT_VIEW) {ContentViewHolder(LayoutInflater.from(mContext).inflate(R.layout.list_item_chat_message, viewGroup, false))} else {HeaderFooterView(mHeaderViewList[viewType - VIEW_TYPE_HEADER_VIEW])}}override fun onBindViewHolder(viewHolder: ItemViewHolder, position: Int) {if (position >= getHeaderViewSize()) {viewHolder.bindViewHolder(position - getHeaderViewSize())}}override fun getItemCount(): Int {return getHeaderViewSize() + mContent.size}fun addHeaderView(headerView: View) {this.mHeaderViewList.add(headerView)}open fun getHeaderViewSize(): Int {return mHeaderViewList.size}fun setContent(contentList: MutableList?) {mContent.clear()if (contentList != null) {mContent.addAll(contentList)}notifyDataSetChanged()}open class ItemViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {open fun bindViewHolder(position: Int) {}}private inner class ContentViewHolder(itemView: View) : ItemViewHolder(itemView) {private var ivUser: ImageView = itemView.findViewById(R.id.iv_user)private var tvMessageUser: TextView = itemView.findViewById(R.id.tv_message_user)private var tvMessageMine: TextView = itemView.findViewById(R.id.tv_message_mine)private var ivMine: ImageView = itemView.findViewById(R.id.iv_mine)override fun bindViewHolder(position: Int) {var message = mContent.getOrNull(position)if (message?.isMine == true) {ivUser.visibility = View.INVISIBLEivMine.visibility = View.VISIBLEtvMessageUser.visibility = View.GONEtvMessageMine.visibility = View.VISIBLEtvMessageMine.text = message.msg_content} else {ivUser.visibility = View.VISIBLEivMine.visibility = View.INVISIBLEtvMessageUser.visibility = View.VISIBLEtvMessageUser.text = message?.msg_contenttvMessageMine.visibility = View.GONE}}}private class HeaderFooterView(itemView: View) : ItemViewHolder(itemView)class ChatMessage {var id: Int = 0var msg_content: String? = nullvar isMine: Boolean = false}}

ChatMessageActivity实现了简单的界面逻辑，利用Timer，我们我们每隔一段时间刷线最新消息。requestNewMessage()和requestMessage()接口分别用来刷新最新消息和下拉以前的消息。

class ChatMessageActivity : Activity() {private lateinit var mRecyclerView: CustomRecyclerViewprivate lateinit var mRefreshViewCreator: RefreshViewCreator// 第一条信息，下拉时使用private var mFirstMessage: ChatMessageAdapter.ChatMessage? = null// 最后一条信息，刷新时使用private var mLastMessage: ChatMessageAdapter.ChatMessage? = nullprivate lateinit var mMessageAdapter: ChatMessageAdapterprivate var mTimer: Timer = Timer(false)private var mTimerTask: TimerTask = object : TimerTask() {override fun run() {requestNewMessage()}}private val mRefreshListener: RefreshViewCreator.IOnRefreshListener =object : RefreshViewCreator.IOnRefreshListener {override fun onRefresh() {requestMessage()}}override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_application_chat_message)mRecyclerView = findViewById(R.id.recycler_view)mMessageAdapter = ChatMessageAdapter(this)mRecyclerView.adapter = mMessageAdaptermRefreshViewCreator = CustomRefreshViewCreator(mRefreshListener)mRecyclerView.setRefreshViewCreator(mRefreshViewCreator)mMessageAdapter.addHeaderView(mRefreshViewCreator.onCreateRefreshView(this, mRecyclerView)!!)}override fun onResume() {super.onResume()mTimer.scheduleAtFixedRate(mTimerTask, 0, 10000)}override fun onPause() {super.onPause()mTimer.cancel()}// 刷新最新消息private fun requestNewMessage() {}// 下拉刷新private fun requestMessage() {}}

显示如下

2. 聊天工具优化

简易聊天工具界面已经搭建好了，但是在实际应用中，我们遇到了三个需要优化的点，

• 软键盘弹出时会覆盖掉最新的消息内容。
• 刷新到最新信息时没有及时显示。
• 下拉刷新时显示最新消息，无法定位，体验不佳。

2.1 优化软键盘

你需要监听软键盘显示的事件，详见Android 监听软键盘显示和隐藏，同时我们滚动列表到指定位置，

window.decorView.addOnLayoutChangeListener { v, left, top, right, bottom, oldLeft, oldTop, oldRight, oldBottom ->// 获取当前屏幕内容的高度var screenHeight = window.decorView.height// 获取View可见区域的bottomvar rect = Rect()window.decorView.getWindowVisibleDisplayFrame(rect)// 需要避免底下导航栏的显示和隐藏操作引发的问题if (screenHeight - rect.bottom > 300) {if (!mShowSoftKeyBoard) {mShowSoftKeyBoard = trueif (mRecyclerView.canScrollVertically(1)) {mRecyclerView.scrollBy(0, screenHeight - rect.bottom)}}} else {mShowSoftKeyBoard = false}
}

2.2 优化刷新最新消息

当RecyclerView有最新消息，如何判断是否需要滚动到最新消息呢，我们通过canScrollVertically(direction)来判断是否在等待新消息。

private fun addMessageList(messageList: MutableList) {if (messageList.isNotEmpty()) {var scrollToBottom = !mRecyclerView.canScrollVertically(1)mMessageList.addAll(messageList)mFirstMessage = mMessageList.first()mLastMessage = mMessageList.last()mMessageAdapter.setContent(mMessageList)if (scrollToBottom) {mRecyclerView.smoothScrollToPosition(mMessageAdapter.itemCount - 1)}}
}

2.3 优化下拉刷新

下拉后，理想的状态是我们保持所有的消息当前所处的位置。所以我们计算获取新消息的高度总和，并进行偏移计算。

private fun insertMessageList(messageList: MutableList) {if (messageList.isNotEmpty()) {mMessageList.addAll(0, messageList)mFirstMessage = mMessageList.first()mLastMessage = mMessageList.last()mMessageAdapter.setContent(mMessageList)var totalHeight = 0for (index in 0 until messageList.size) {totalHeight += getItemHeight(index)}mRecyclerView.scrollBy(0, totalHeight)}mRefreshViewCreator.refreshFinish()
}private fun getItemHeight(position: Int): Int {var viewHolder = mMessageAdapter.onCreateViewHolder(mRecyclerView,mMessageAdapter.getItemViewType(mMessageAdapter.getHeaderViewSize() + position))viewHolder.bindViewHolder(position)viewHolder.itemView.measure(View.MeasureSpec.makeMeasureSpec(mRecyclerView.width, View.MeasureSpec.EXACTLY),View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED))return viewHolder.itemView.measuredHeight
}

效果如下

当然，我们有时候会显示消息的时间，这样导致数据高度会变化，可以如下优化。

var layoutManager = mRecyclerView.layoutManager as LinearLayoutManager
var itemHeight = layoutManager.findViewByPosition(1)?.height ?: 0var totalHeight = 0
for (index in 0 until messageList.size + 1) {totalHeight += getItemHeight(index)
}
mRecyclerView.scrollBy(0, totalHeight - itemHeight)

源码下载: https://github.com/nai-chen/AndroidBlog

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