安卓软件开发：基于Jetpack Compose实现Redux架构

// AppState.kt
data class AppState(
    val loginState: LoginState = LoginState()
)

data class LoginState(
    val isLoading: Boolean = false,
    val isLoggedIn: Boolean = false,
    val username: String = "",
    val errorMsg: String? = null
)

// LoginAction.kt
sealed class LoginAction {
    data class Login(val username: String, val password: String) : LoginAction()
    object LoginSuccess : LoginAction()
    data class LoginFailure(val errorMsg: String) : LoginAction()
    object Logout : LoginAction()
}

// AppReducer.kt
fun appReducer(state: AppState, action: Any): AppState {
    return state.copy(
        loginState = loginReducer(state.loginState, action)
    )
}
fun loginReducer(state: LoginState, action: Any): LoginState {
    when (action) {
        is LoginAction.Login -> {
            return state.copy(
                isLoading = true,
                errorMsg = null,
                username = action.username
) }
        is LoginAction.LoginSuccess -> {
            return state.copy(
                isLoading = false,
                isLoggedIn = true
            )
        }
        is LoginAction.LoginFailure -> {
            return state.copy(
                isLoading = false,
                errorMsg = action.errorMsg
) }
        is LoginAction.Logout -> {
            return state.copy(
                isLoggedIn = false,
                username = "",
                errorMsg = null
) }
        else -> return state
    }
}

class Store(
    initialState: AppState,
    private val reducer: (AppState, Any) -> AppState
){
private val _state = MutableStateFlow(initialState) val state: StateFlow<AppState> = _state.asStateFlow()
    fun dispatch(action: Any) {
        val currentState = _state.value
val newState = reducer(currentState, action)
        _state.value = newState
    }
}
    initialState = AppState(),
    reducer = ::appReducer
)

class LoginViewModel : ViewModel() {

    //  Store 通过依赖注入或直接引用全局单例
    private val store = Store(
        initialState = AppState(),
        reducer = ::appReducer
    )

    // 将状态暴露为 StateFlow 给 UI层
    val loginState: StateFlow<LoginState> = store.state.map { it.loginState }
        .stateIn(viewModelScope, SharingStarted.Eagerly, store.state.value.loginState)

    fun login(username: String, password: String) {
        // 先dispatch：告诉redux正在登陆
        store.dispatch(LoginAction.Login(username, password))

        viewModelScope.launch {
            // 模拟网络延迟
            delay(2000)

            // 简单判断下密码：假设密码是 "123456" 则成功，否则失败
            if (password == "123456") {
                store.dispatch(LoginAction.LoginSuccess)
            } else {
                store.dispatch(LoginAction.LoginFailure("密码错误"))
            }
        }
    }

    fun logout() {
        store.dispatch(LoginAction.Logout)
    }
}
 

@Composable
fun LoginScreen(
    viewModel: LoginViewModel = viewModel() // 通过DI传入
) {
    val loginState by viewModel.loginState.collectAsState()

    // 登录表单本地State（也可以放到Redux管理，但通常只放必要的全局数据到Redux）
    var username by remember { mutableStateOf("") }
    var password by remember { mutableStateOf("") }

    // 注意：登陆后的 username 也可能和本地输入框不一致
    // 如果希望登录前和登录成功后都绑定同一个变量，可以只用 Redux State 中的 username。

    Scaffold(
        topBar = {
            TopAppBar(title = { Text("Redux + Nim Login") })
        }
    ) { innerPadding ->
        Column(
            modifier = Modifier
                .padding(innerPadding)
                .fillMaxSize()
                .padding(16.dp),
            verticalArrangement = Arrangement.Center
        ) {
            // 显示登录状态
            Text(text = "Logged In: ${loginState.isLoggedIn}")

            OutlinedTextField(
                value = username,
                onValueChange = { username = it },
                label = { Text("用户名") },
                modifier = Modifier.fillMaxWidth()
            )

            Spacer(modifier = Modifier.height(8.dp))

            OutlinedTextField(
                value = password,
                onValueChange = { password = it },
                label = { Text("密码") },
                modifier = Modifier.fillMaxWidth(),
                visualTransformation = PasswordVisualTransformation()
            )

            Spacer(modifier = Modifier.height(16.dp))

            // 显示错误
            loginState.errorMsg?.let { error ->
                Text(
                    text = error,
                    color = Color.Red,
                    modifier = Modifier.padding(bottom = 8.dp)
                )
            }

            // 显示加载进度
            if (loginState.isLoading) {
                CircularProgressIndicator()
            } else {
                // 如果没有在加载，就显示登录按钮或退出按钮
                if (!loginState.isLoggedIn) {
                    Button(
                        onClick = {
                            viewModel.login(username, password)
                        },
                        modifier = Modifier.fillMaxWidth()
                    ) {
                        Text("登录")
                    }
                } else {
                    // 已经登录了
                    Button(
                        onClick = {
                            viewModel.logout()
                        },
                        modifier = Modifier.fillMaxWidth()
                    ) {
                        Text("退出登录")
                    }
                }
            }
        }
    }
}