本文已授权微信公众号：鸿洋  在微信公众号平台原创首发。RecyclerView复杂适配器的“终极形态”?代码更解耦

前言

RecyclerView是Android开发中很常用的控件,市面上也有很多种封装,使其更易用,但是面对复杂的适配器需求,则很难做到逻辑清晰且解耦,比如聊天消息的适配器

正文

1.首先我们用最原始的方法写一个简单的聊天消息的rv

实现图如下:

代码如下:

class MainActivity : AppCompatActivity() {//数据源: type to dataval msgData = mutableListOf<Pair<Int, Any>>(1 to "文本消息",2 to R.drawable.ic_launcher,//图片消息3 to "tips消息",1 to "文本消息2",4 to "不支持的消息",)override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)//初始化rvval rv = RecyclerView(this)setContentView(rv)val llm = LinearLayoutManager(this)llm.orientation = LinearLayoutManager.VERTICALrv.layoutManager = llm//适配器rv.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): RecyclerView.ViewHolder {//根据不同的viewType创建不同的viewHolderreturn when (viewType) {1 -> TextVH(parent)2 -> ImageVH(parent)3 -> TipsVH(parent)else -> NoMatchVH(parent)}}override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {//判断相应type,并根据数据展示相应的viewwhen (getItemViewType(position)) {1 -> {(holder.itemView as TextView).text = msgData[position].second.toString()}2 -> {(holder.itemView as ImageView).setImageResource(msgData[position].second as Int)}3 -> {(holder.itemView as TextView).text = msgData[position].second.toString()}}}override fun getItemCount(): Int = msgData.size//条目的数量override fun getItemViewType(position: Int): Int =msgData[position].first//条目的type,使用数据源的type}}//文字的vhclass TextVH(parent: ViewGroup) : RecyclerView.ViewHolder(TextView(parent.context).apply {textSize = 22f})//图片的vhclass ImageVH(parent: ViewGroup) : RecyclerView.ViewHolder(ImageView(parent.context))//提示性文字的vhclass TipsVH(parent: ViewGroup) : RecyclerView.ViewHolder(TextView(parent.context))//没有匹配到现有type的vh,可能是新版本的消息class NoMatchVH(parent: ViewGroup) : RecyclerView.ViewHolder(TextView(parent.context)) }

这时我们发现,设置view数据都集中在了onBindViewHolder方法中,类型多了或者逻辑多了后会造成方法非常臃肿,所以我们抽出来一个BaseViewolder出来,将设置view数据的方法抽出来,代码如下:

class MainActivity : AppCompatActivity() {//数据源: type to dataval msgData = mutableListOf<Pair<Int, Any>>(1 to "文本消息",2 to R.drawable.ic_launcher,//图片消息3 to "tips消息",1 to "文本消息2",4 to "不支持的消息",)override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)//初始化rvval rv = RecyclerView(this)setContentView(rv)val llm = LinearLayoutManager(this)llm.orientation = LinearLayoutManager.VERTICALrv.layoutManager = llm//适配器rv.adapter = object : RecyclerView.Adapter<BaseVH>() {override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): BaseVH {//根据不同的viewType创建不同的viewHolderreturn when (viewType) {1 -> TextVH(parent)2 -> ImageVH(parent)3 -> TipsVH(parent)else -> NoMatchVH(parent)}}override fun onBindViewHolder(holder: BaseVH, position: Int) { //**************调用setData方法让viewHolder根据数据展示相应的viewholder.setData(msgData[position].second)}override fun getItemCount(): Int = msgData.size//条目的数量override fun getItemViewType(position: Int): Int =msgData[position].first//条目的type,使用数据源的type}}//******统一封装vh的setData方法,使其解耦abstract class BaseVH(val parent: ViewGroup, val view: View) :RecyclerView.ViewHolder(view) {abstract fun setData(data: Any)}//文字的vhclass TextVH(parent: ViewGroup) : BaseVH(parent, TextView(parent.context).apply {textSize = 22f}) {override fun setData(data: Any) {(view as TextView).text = data as String}}//图片的vhclass ImageVH(parent: ViewGroup) : BaseVH(parent, ImageView(parent.context)) {override fun setData(data: Any) {(view as ImageView).setImageResource(data as Int)}}//提示性文字的vhclass TipsVH(parent: ViewGroup) : BaseVH(parent, TextView(parent.context)) {override fun setData(data: Any) {(view as TextView).text = data as String}}//没有匹配到现有type的vh,可能是新版本的消息class NoMatchVH(parent: ViewGroup) : BaseVH(parent, TextView(parent.context)) {override fun setData(data: Any) {(view as TextView).text = "暂不支持的消息,请更新应用"}} }

但是看到上面创建viewholder的方法onCreateViewHolder,新增或修改type还是得每次自己手动修改

所以我们可以使用一个map,以type为key,并将需要创建的viewHolder的构造传进去,如下:

//装type:viewHolder构造的mapval viewHolderMap = HashMap<Int, (ViewGroup) -> BaseVH>().apply {put(1, ::TextVH)put(2, ::ImageVH)put(3, ::TipsVH)}//并修改创建viewHolder的方法override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): BaseVH {//根据不同的viewType创建不同的viewHolderreturn (viewHolderMap[viewType] ?: ::NoMatchVH).invoke(parent)}

 这样改造后,adapter中几乎就没有什么代码了,代码都移动到了各自的viewHolder中了,但是在新增viewHolder类型的时候这个viewHolderMap比较容易被忽略,能不能让他自动将所有BaseVH的子类构造和相应的type添加进去呢?

java能通过反射拿到一个类所有的子类吗?能也不能,实现起来很麻烦,而且在安卓系统上不一定行得通,但是kotlin反射可以

kotlin反射可以获取密封类(sealed class)的所有直接子类,所以我们可以改造下

将BaseVH改为sealed class,然后在初始化adapter的时候通过kotlin的反射来获取所有直接子类的构造(或class)

ps:使用kotlin的反射需要引入反射包

//kotlin反射implementation("org.jetbrains.kotlin:kotlin-reflect:$kotlinVersion")

然后修改成如下代码:

class MainActivity : AppCompatActivity() {//数据源: type to dataval msgData = mutableListOf<Pair<Int, Any>>(1 to "文本消息",2 to R.drawable.ic_launcher,//图片消息3 to "tips消息",1 to "文本消息2",4 to "不支持的消息",)companion object {//******装type:viewHolder构造的mapval viewHolderMap = HashMap<Int, Constructor<out BaseVH>>()init {val fl = FrameLayout(App.instance)//******遍历class并构建出对象获取其type,并自动注册到viewHolderMap中BaseVH::class.sealedSubclasses.forEach {val constructor = it.java.getConstructor(ViewGroup::class.java)val baseVH = constructor.newInstance(fl)viewHolderMap[baseVH.type] = constructor}}}override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)//初始化rvval rv = RecyclerView(this)setContentView(rv)val llm = LinearLayoutManager(this)llm.orientation = LinearLayoutManager.VERTICALrv.layoutManager = llm//适配器rv.adapter = object : RecyclerView.Adapter<BaseVH>() {override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): BaseVH { //**************根据不同的viewType创建不同的viewHolderreturn viewHolderMap[viewType]?.newInstance(parent) ?: NoMatchVH(parent)}override fun onBindViewHolder(holder: BaseVH, position: Int) {//调用setData方法让viewHolder根据数据展示相应的viewholder.setData(msgData[position].second)}override fun getItemCount(): Int = msgData.size//条目的数量override fun getItemViewType(position: Int): Int =msgData[position].first//条目的type,使用数据源的type}}//统一封装vh的setData方法,使其解耦sealed class BaseVH(val parent: ViewGroup, val view: View) :RecyclerView.ViewHolder(view) {abstract val type: Intabstract fun setData(data: Any)}//文字的vhclass TextVH(parent: ViewGroup) : BaseVH(parent, TextView(parent.context).apply {textSize = 22f}) {override val type = 1override fun setData(data: Any) {(view as TextView).text = data as String}}//图片的vhclass ImageVH(parent: ViewGroup) : BaseVH(parent, ImageView(parent.context)) {override val type = 2override fun setData(data: Any) {(view as ImageView).setImageResource(data as Int)}}//提示性文字的vhclass TipsVH(parent: ViewGroup) : MainActivity.BaseVH(parent, TextView(parent.context)) {override val type = 3override fun setData(data: Any) {(view as TextView).text = data as String}}//没有匹配到现有type的vh,可能是新版本的消息class NoMatchVH(parent: ViewGroup) : MainActivity.BaseVH(parent, TextView(parent.context)) {override val type = 99999override fun setData(data: Any) {(view as TextView).text = "暂不支持的消息,请更新应用"}} }

这样改造后,就可以直接继承BaseVH,并重写一下type,就可以自动注册了,减少大脑负担

ps:在BaseVH中加一个abstract的type,这样子类不重写type就编译不过去,但是需要统一构造的入参类型,并且有点骚操作; 如果不想这样处理的话,可以将type改为静态的,然后可以直接通过class反射获取type的值,或将type放到类名上(骚操作).但后两种方法是没有编译时提醒的,很容易忘.

结语

上面的方案就是我认为的RecyclerView复杂适配器且更解耦的终极形态.

扩展

要问还有更好的方式吗?

我觉得有!那就是使用compose,当然目前用compose的人或公司很少,但也是一种比较超前的而且我觉得是未来的终极形态,代码如下:

//数据源: type to dataval msgData = mutableListOf<Pair<Int, Any>>(1 to "文本消息",2 to R.drawable.ic_launcher,//图片消息3 to "tips消息",1 to "文本消息2",4 to "不支持的消息",)override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContent {//compose的竖向RecyclerViewLazyColumn(Modifier.fillMaxSize()) {//遍历数据源,展示数据对应的viewmsgData.forEach {item {//根据type的不同展示不同的view(ItemFunctions.itemFunctionMap[1]?: ItemFunctions::NoMatchItem_99999).invoke(it.second)}}}}}object ItemFunctions {@Composablefun TextItem_1(any: Any) {Text(text = any as String, fontSize = 22.sp)}@Composablefun ImgItem_2(any: Any) {Image(painter = painterResource(id = any as Int), contentDescription = "")}@Composablefun TipsItem_3(any: Any) {Text(text = any as String)}@Composablefun NoMatchItem_99999(any: Any) {Text(text = "暂不支持的消息,请更新应用")}@JvmStaticval itemFunctionMap = HashMap<Int, @Composable (Any) -> Unit>()init {ItemFunctions::class.functions.filter { it.javaMethod?.declaringClass == ItemFunctions::class.java }.forEach {val type = it.name.split('_').lastOrNull()?.toIntOrNull() ?: return@forEachitemFunctionMap[type] = it as @Composable (Any) -> Unit}}}

ps:这里使用了骚操作,将type放在了方法名的末尾

pps:这段代码目前是运行不起来的,因为kotlin暂时还不支持引用@Composable的Function,但能运行起来也是和上面View展示的一样的效果

ppps:当然也可以在msgData.forEach{}内用when来做,但后续type都得手动添加,如下:

//数据源: type to dataval msgData = mutableListOf<Pair<Int, Any>>(1 to "文本消息",2 to R.drawable.ic_launcher,//图片消息3 to "tips消息",1 to "文本消息2",4 to "不支持的消息",)override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContent {//compose的竖向RecyclerViewLazyColumn(Modifier.fillMaxSize()) {//遍历数据源,展示数据对应的viewmsgData.forEach {item {//根据type的不同展示不同的viewwhen (it.first) {1 -> TextItem(any = it.second)2 -> ImgItem(any = it.second)3 -> TipsItem(any = it.second)else -> NoMatchItem()}}}}}}@Composablefun TextItem(any: Any) {Text(text = any as String, fontSize = 22.sp)}@Composablefun ImgItem(any: Any) {Image(painter = painterResource(id = any as Int), contentDescription = "")}@Composablefun TipsItem(any: Any) {Text(text = any as String)}@Composablefun NoMatchItem() {Text(text = "暂不支持的消息,请更新应用")}

end

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