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近期android开发，遇到的需求，分享二个android可能用到的小组件

 下拉选择器：它的实现，主要是需要监听它依附的组件当前距离屏幕顶端的位置。

                     在显示下拉菜单中，如果需要点击上面有响应。可通过activity拿到decorview(activity.window.decorView),然后把下拉的view添加到decorView，然后设置该菜单距离顶端的上边距。如果需要先点击屏幕让菜单先消失，可搞一个全屏的下拉菜单，距顶端高度搞一个透明的view来填充（设置一个点击事件，处理decorView.remove该下拉组件）

object DropDownItemsUtils {const val DROP_DOWN_ID = -1000fun showDropDownView(activity: Activity,marginTopPx:Float,list:List<String>,selectIndex:Int = -1,onItemClick: ((pos: Int?) -> Unit)?=null){val decorView = activity.window.decorView as ViewGroupdecorView.findViewById<View>(DROP_DOWN_ID)?.let {decorView.removeView(it)}val composeView = ComposeView(activity).apply {setViewCompositionStrategy(ViewCompositionStrategy.DisposeOnViewTreeLifecycleDestroyed)setContent{DropDownItems(modifier = Modifier.fillMaxWidth().wrapContentHeight(), list = list, selectIndex = selectIndex) {decorView.removeView(this@apply)onItemClick?.invoke(it)}}id = DROP_DOWN_ID}val lp = FrameLayout.LayoutParams(-1,-1)lp.topMargin = marginTopPx.toInt()decorView.addView(composeView,lp)}fun dismissDropDownView(activity: Activity){val decorView = activity.window.decorView as ViewGroupdecorView.findViewById<View>(DROP_DOWN_ID)?.let {decorView.removeView(it)}}
}

级联选择器：它的承载容器是一个底部弹窗的 DialogFragment,显示的内容目前我用compose实现，已选的级联它横向显示采用的LazyRow，列表项使用LazyColumn实现。具体实现如下。

data class LevelsItem(val text:String,var list:List<LevelsItem>? = null,var parentId:String? = null,var level:Int? = null,val tag:Any? = null //LevelsItem，是从服务端给的数据模型转的，实际可以再转化的时候，将该tag    //设置为服务端给的模型.如下我转换的代码
)
/**fun convertMotorcadeRespToLevelsItem(list: List<MotorcadeResp>): List<LevelsItem> {return list.map { motorcadeResp ->LevelsItem(text = motorcadeResp.name ?: "", // Map name to textparentId = motorcadeResp.parentId,level = motorcadeResp.departmentLevel,list = motorcadeResp.childDepartment?.let { convertMotorcadeRespToLevelsItem(it) }, // Recursively map childDepartmenttag = motorcadeResp // Set the original MotorcadeResp as tag)}}
*/

/*** 级联选择，可以自行选择。自行点击确定，完成选择成功*/
class LevelsSelector1Dialog : BottomDialogFragment() {private val SELECTSTR: String = "-10000000"var title: String? = nullvar list: List<LevelsItem> = ArrayList()var onConfirm: ((LevelsItem?) -> Unit)? = null//用来横向显示tab项列表的itemprivate var currentSelectItem: SnapshotStateList<LevelsItem> = mutableStateListOf()//记录当前选择的值，最后用来点击确定，来回调给调用方使用的private var currentSelectItemVal: SnapshotStateList<LevelsItem> = mutableStateListOf()override fun onCreateView(inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?): View {return ComposeView(requireContext()).apply {setViewCompositionStrategy(ViewCompositionStrategy.DisposeOnViewTreeLifecycleDestroyed)setContent {WelcomeAssistantTheme {LevelsSelectorScreen()}}}}@Preview(widthDp = 375, heightDp = 812)@Composableprivate fun LevelsSelectorScreen() {currentSelectItem.clear()//横向tab，添加一个默认项 “请选择"currentSelectItem.add(LevelsItem(SELECTSTR, list))val height =(0.64f * requireContext().resources.displayMetrics.heightPixels) / LocalDensity.current.densityBox(modifier = Modifier.fillMaxWidth().height(height.dp).background(color = Color.White,shape = RoundedCornerShape(topStart = 24.dp,topEnd = 24.dp,bottomStart = 0.dp,bottomEnd = 0.dp)).padding(16.dp)) {Image(painterResource(R.mipmap.ic_levels_selector_close),modifier = Modifier.clickable {dismiss()}.size(24.dp).align(Alignment.TopEnd),contentDescription = null)Text(modifier = Modifier.padding(top = 24.dp, bottom = 16.dp).align(Alignment.TopCenter),text = title ?: "",style = buildMSDBTextStyle(fontSize = 20.sp, color = ff0A1733))val listItems = remember {mutableStateOf(list)}val currentSelectTabIndex = remember {mutableIntStateOf(0)}LazyRow(modifier = Modifier.padding(top = 68.dp).fillMaxWidth().height(30.dp),) {itemsIndexed(currentSelectItem) {index, selectItem ->Column {if (SELECTSTR == selectItem.text) {Text(modifier = Modifier.padding(end = 24.dp).singleClickable {if(currentSelectTabIndex.intValue == index){return@singleClickable}currentSelectTabIndex.intValue = indexlistItems.value =currentSelectItem[index - 1].list ?: ArrayList()},text = stringResource(R.string.levels_select),style = buildMSDNTextStyle(color = FF9DA2AD, fontSize = 16.sp))} else {Text(modifier = Modifier.padding(end = 24.dp).widthIn(max = 110.dp).singleClickable {if(currentSelectTabIndex.intValue == index){return@singleClickable}if (index >= 1) {listItems.value =currentSelectItem[index - 1].list ?: ArrayList()} else {listItems.value =currentSelectItem[currentSelectItem.size - 1].list?: ArrayList()}currentSelectTabIndex.intValue = index},text = selectItem.text,style = buildMSDBTextStyle(color = ff0A1733,fontSize = 16.sp,),overflow = TextOverflow.Ellipsis,maxLines = 1)}if(currentSelectTabIndex.intValue == index) {Box(modifier = Modifier.align(Alignment.CenterHorizontally).padding(end = 24.dp).height(3.dp).width(24.dp).background(color = FF306DF4, shape = RoundedCornerShape(3.dp)))}}}}LazyColumn(modifier = Modifier.padding(top = 108.dp, bottom = 70.dp).fillMaxSize()) {var currentLevelSelectItem: LevelsItem? = nullitemsIndexed(listItems.value) {i, levelsItem ->var isAlreadySelectItem = currentSelectItemVal.contains(levelsItem)if (isAlreadySelectItem) {currentLevelSelectItem = levelsItem}Row(modifier = Modifier.fillMaxWidth().padding(vertical = 12.dp).singleClickable {//子item会有很多，可以判断当前item的父id是否相同val index = currentSelectItem.indexOfFirst {it.parentId == levelsItem.parentId}//可选项是否还有子列表if (levelsItem.list.isNullOrEmpty()) {//级联最后的那个列表if (currentLevelSelectItem != null) {currentSelectItemVal.removeRange(currentSelectItemVal.indexOf(currentLevelSelectItem),currentSelectItemVal.size)}isAlreadySelectItem = trueif(index > 0){currentSelectItem.removeAt(index)}currentSelectItemVal.add(levelsItem)} else {//可以点出下一个级联if (index < 0) {currentSelectItem.add(currentSelectItem.size - 1,levelsItem)} else {currentSelectItem.removeAt(index)currentSelectItem.add(index,levelsItem)}currentSelectTabIndex.intValue += 1listItems.value = levelsItem.list ?: ArrayList()if (!isAlreadySelectItem) {if (currentLevelSelectItem != null) {currentSelectItemVal.removeRange(currentSelectItemVal.indexOf(currentLevelSelectItem), currentSelectItemVal.size)}currentSelectItemVal.add(levelsItem)}}}) {Row(modifier = Modifier.fillMaxWidth()) {Text(modifier = Modifier.weight(1f),text = levelsItem.text,style = buildMSDNTextStyle(color = if (isAlreadySelectItem) FF306DF4 else ff0A1733,fontSize = 16.sp))if (isAlreadySelectItem) {Image(modifier = Modifier.size(24.dp),painter = painterResource(R.mipmap.ic_dialog_levels_check),contentDescription = null)}}}}}Spacer(modifier = Modifier.align(alignment = Alignment.BottomCenter).padding(bottom = 69.5.dp).height(0.5.dp).fillMaxSize().background(color = FFF2F3F4))Box(modifier = Modifier.align(alignment = Alignment.BottomCenter).padding(start = 16.dp, end = 16.dp, bottom = 16.dp).fillMaxWidth().height(40.dp).background(color = FF306DF4, RoundedCornerShape(24.dp)).singleClickable {if (currentSelectItemVal.size > 0) {onConfirm?.invoke(currentSelectItemVal[currentSelectItemVal.size - 1])} else {onConfirm?.invoke(null)}dismiss()},contentAlignment = Alignment.Center) {Text(text = stringResource(R.string.dialog_confirm_position_txt),style = TextStyle(color = Color.White, fontSize = 14.sp))}}}}