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Kotlin Multiplatform Mobile（KMM）已经从一个雄心勃勃的想法发展成为一个稳定而强大的框架，为开发人员提供了在多个平台上无缝共享代码的能力。通过最近的稳定版本里程碑，KMM已成为跨平台开发领域的改变者。

环境设置

带有Kotlin Multiplatform插件的Android Studio

设置Koin和Ktor

1. 将两个依赖项添加到：shared模块中，我使用gradlelibrary目录作为依赖项。 io.insert-koin:koin-core:3.5.0
2. 对于Ktor，根据您的API，有多个依赖项各自具有自己的目的。
3. 由于注入将在平台级别进行，因此我们需要将初始化部分暴露给两个平台。为此，我们将创建一个带有initKoin()方法的Helper类，并从iOS和Android的应用程序类调用此方法。
4. initKoin() → 我们在这里定义我们稍后需要的所有依赖项。

//shared/src/commonMain/kotlin/di/Koin.kt
fun initKoin() = startKoin {modules(networkModule)
}
private val networkModule = module {single {HttpClient {defaultRequest {url.takeFrom(URLBuilder().takeFrom("https://internshala.com/"))}install(HttpTimeout) {requestTimeoutMillis = 15_000}install(ContentNegotiation) {json(Json {ignoreUnknownKeys = trueprettyPrint = true})}install(Logging) {level = LogLevel.ALLlogger = object : Logger {override fun log(message: String) {println(message)}}}}}
}

2个平台调用此方法：

1. iOS：我们需要在2个不同的文件中进行更改。（共享iOS文件和特定于平台的文件）

// :shared/src/iosMain/kotlin/Koin.ios.kt
class Koin {fun initKoin() {di.initKoin()}
}

// iosApp/iosApp/iOSApp.swift
import SwiftUI
import shared
@main
struct iOSApp: App {var body: some Scene {WindowGroup {ContentView()}}init() {KoinKt.doInitKoin()}

2. Android：与iOS不同，对于Android，我们可以直接调用：shared initKoin()方法并初始化Koin。

class App : Application() {override fun onCreate() {super.onCreate()initKoin()}
}

将API响应与Result类进行映射

我们将在Ktor的HttpClient上编写一个小的扩展，用于执行所有API调用并将响应包装在Result（成功/错误）中，并附带适当的消息。

suspend inline fun <reified T> HttpClient.fetch(block: HttpRequestBuilder.() -> Unit
): Result<T> = try {val response = request(block)if (response.status == HttpStatusCode.OK)Result.Success(response.body())elseResult.Error(Throwable("${response.status}: ${response.bodyAsText()}"))
} catch (e: Exception) {Result.Error(e)
}sealed interface Result<out R> {class Success<out R>(val value: R) : Result<R>data object Loading : Result<Nothing>class Error(val throwable: Throwable) : Result<Nothing>
}

设置分页库

在实施Koin和Ktor之后，接下来是分页库。我们将使用来自cashapp的开源库。 由于Paging提供了多种方法来处理错误和API响应，我们将创建一个组合，以处理这种行为。

@Composable
fun <T : Any> PagingListUI(data: LazyPagingItems<T>,content: @Composable (T) -> Unit
) {LazyColumn(modifier = Modifier.fillMaxSize().background(Color.White),horizontalAlignment = Alignment.CenterHorizontally,) {items(data.itemCount) { index ->val item = data[index]item?.let { content(it) }Divider(color = UiColor.background,thickness = 10.dp,modifier = Modifier.border(border = BorderStroke(0.5.dp, Color.LightGray)))}data.loadState.apply {when {refresh is LoadStateNotLoading && data.itemCount < 1 -> {item {Box(modifier = Modifier.fillParentMaxSize(),contentAlignment = Alignment.Center) {Text(text = "No Items",modifier = Modifier.align(Alignment.Center),textAlign = TextAlign.Center)}}}refresh is LoadStateLoading -> {item {Box(modifier = Modifier.fillParentMaxSize(),contentAlignment = Alignment.Center) {CircularProgressIndicator(color = UiColor.primary)}}}append is LoadStateLoading -> {item {CircularProgressIndicator(color = UiColor.primary,modifier = Modifier.fillMaxWidth().padding(16.dp).wrapContentWidth(Alignment.CenterHorizontally))}}refresh is LoadStateError -> {item {ErrorView(message = "No Internet Connection.",onClickRetry = { data.retry() },modifier = Modifier.fillParentMaxSize())}}append is LoadStateError -> {item {ErrorItem(message = "No Internet Connection",onClickRetry = { data.retry() },)}}}}}
}@Composable
private fun ErrorItem(message: String,modifier: Modifier = Modifier,onClickRetry: () -> Unit
) {Row(modifier = modifier.padding(16.dp),horizontalArrangement = Arrangement.SpaceBetween,verticalAlignment = Alignment.CenterVertically) {Text(text = message,maxLines = 1,modifier = Modifier.weight(1f),color = androidx.compose.ui.graphics.Color.Red)OutlinedButton(onClick = onClickRetry) {Text(text = "Try again")}}
}@Composable
private fun ErrorView(message: String,modifier: Modifier = Modifier,onClickRetry: () -> Unit
) {Column(modifier = modifier.padding(16.dp).onPlaced { _ ->},verticalArrangement = Arrangement.Center,horizontalAlignment = Alignment.CenterHorizontally) {Text(text = message,maxLines = 1,modifier = Modifier.align(Alignment.CenterHorizontally),color = androidx.compose.ui.graphics.Color.Red)OutlinedButton(onClick = onClickRetry, modifier = Modifier.fillMaxWidth().padding(16.dp).wrapContentWidth(Alignment.CenterHorizontally)) {Text(text = "Try again")}}
}

设置App和Internship屏幕的UI部分

我们的应用程序入口点 - App.kt

// :shared/src/commonMain/kotlin/App.kt
@Composable
fun App() {MaterialTheme {val screens = Screen.values()var selectedScreen by remember { mutableStateOf(screens.first()) }Scaffold(bottomBar = {BottomNavigation(backgroundColor = Color.White,modifier = Modifier.height(64.dp)) {screens.forEach { screen ->BottomNavigationItem(modifier = Modifier.background(Color.White),selectedContentColor = ui.theme.Color.textOnPrimary,unselectedContentColor = Color.Gray,icon = {Icon(imageVector = getIconForScreen(screen),contentDescription = screen.textValue)},label = { Text(screen.textValue) },selected = screen == selectedScreen,onClick = { selectedScreen = screen },)}}},content = { getScreen(selectedScreen) })}
}@Composable
fun getIconForScreen(screen: Screen): ImageVector {return when (screen) {Screen.INTERNSHIPS -> Icons.Default.AccountBoxScreen.JOBS -> Icons.Default.AddScreen.COURSES -> Icons.Default.Notificationselse -> Icons.Default.Home}
}@Composable
fun getScreen(selectedScreen: Screen) = when (selectedScreen) {Screen.INTERNSHIPS -> InternshipsScreen().content()Screen.JOBS -> JobsScreen()Screen.COURSES -> CoursesScreen()else -> HomeScreen()
}

获取分页数据的实习界面

class InternshipsScreen : KoinComponent {private val viewModel: InternshipViewModel by inject()@Composablefun content() {val result by rememberUpdatedState(viewModel.internships.collectAsLazyPagingItems())return Scaffold(topBar = {TopAppBar(title = { Text("Internships") },elevation = 0.dp,navigationIcon = {IconButton(onClick = { println("Drawer clicked") }) {Icon(imageVector = Icons.Default.Menu, contentDescription = "Menu")}},actions = {IconButton(onClick = { println("Search Internships!") }) {Icon(imageVector = Icons.Default.Search, contentDescription = "Search")}},backgroundColor = Color.White)},drawerContent = { /*Drawer content*/ },content = { PagingListUI(data = result, content = { InternshipCard(it) }) },)}
}

总结：

KMM是一个在多个平台上无缝共享代码的能力的框架。已成为跨平台开发领域的改变者。后续我会自己实战一个KMM项目，包括Ktor的详细讲解，敬请期待。