使用flow实现Android_App登录

build.gralde(:app)

dependencies {

    implementation 'androidx.core:core-ktx:1.6.0'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'

    //Activity KTX for viewModels()
    implementation("androidx.activity:activity-ktx:1.3.1")

    //Architectural Components
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.1")

    //Coroutines
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.0")
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.4.3")

    //Coroutine Lifecycle Scopes
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.1")
    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.3.1")

    kapt "com.android.databinding:compiler:3.1.4"

}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    private val viewModel by viewModels<MainViewModel>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater).also { binding->
            setContentView(binding.root)
        }
        lifecycleScope.launchWhenStarted {
            viewModel.loginUiState.collect {
                when(it) {
                    is MainViewModel.LoginUiState.Success -> {
                        Snackbar.make(
                            binding.root,
                            "登录成功",
                            Snackbar.LENGTH_LONG
                        ).show()
                        binding.progressBar.isVisible = false
                    }
                    is MainViewModel.LoginUiState.Error -> {
                        Snackbar.make(
                            binding.root,
                            it.message,
                            Snackbar.LENGTH_LONG
                        ).show()
                        binding.progressBar.isVisible = false
                    }
                    is MainViewModel.LoginUiState.Loading -> {
                        binding.progressBar.isVisible = true
                    }
                    else -> Unit
                }
            }
        }
        //点击发起登录
        binding.btnLogin.setOnClickListener {
            viewModel.login(
                binding.username.text.toString(),
                binding.password.text.toString())
        }
    }
}

MainViewModel.kt

class MainViewModel : ViewModel() {
    private val _loginUiState = MutableStateFlow<LoginUiState>(LoginUiState.Empty)
    val loginUiState: StateFlow<LoginUiState> = _loginUiState

    fun login(username: String, password: String) = viewModelScope.launch {
        _loginUiState.value = LoginUiState.Loading
        delay(2000L)
        if (username == "android" && password == "123456") {
            _loginUiState.value = LoginUiState.Success
        } else {
            _loginUiState.value = LoginUiState.Error("密码错误")
        }
    }

    sealed class LoginUiState {
        object Success : LoginUiState()
        data class Error(val message: String) : LoginUiState()
        object Loading : LoginUiState()
        object Empty : LoginUiState()
    }
}