How to implement login activity architecture using android architecture components?

Question

I understand how to use ViewModel, Repositories and Room for transfer data from database to screen. But how implement login activity with POST method. Do I need create LiveData isAuthorized from ViewModel or AuthorizationRepository? Can anyone show example about using command methods with android architecture components?

Answer 1

This can be your login class, maybe extending ViewModel, so it keeps alive on configuration changes:

 class LoginClass
    {
        var loginEvent = SingleLiveEvent<LoginEvent>()
        fun startLogin(user: String, password: String)
        {
            loginEvent.value= LoginEvent(LoginStatus.LoginStart,null,null)
            launch(UI) { 
                try{
                    bg{
                        //do login process
                    }.await()
                    loginEvent.value= LoginEvent(LoginStatus.LoginOk,null,null)
                }
                catch (error: Exception){
                    loginEvent.value= LoginEvent(LoginStatus.LoginFailed,error.message,null)
                }
            }
        }
        data class LoginEvent(var loginStatus: LoginStatus, var errorMessage: String?, var loginExtraData: Any?) 
        enum class LoginStatus
        {
            LoginStart,
            LoginOk,
            LoginFailed
        }
    }

You can observe the login status to react and change your UI accordingly:

val myLoginClass = LoginClass()
myLoginClass.loginEvent.observe(this@LifecycleOwner, Observer {
    if(it==null)
        return@Observer
    when(it.loginStatus)
    {

        LoginClass.LoginStatus.LoginStart -> {
            //show indeterinate progress bar, disable inputs, etc
        }
        LoginClass.LoginStatus.LoginOk -> {
            //go to logged in activity
        }

        LoginClass.LoginStatus.LoginFailed -> {
            //show login failed toast, hide progress bar, enable input, etc
        }
    }
})

To start login simply call the login method of your class:

loginButton.onClick {
    myLoginClass.startLogin("user", "password")
}

Logically, you will need more than this, but you can use it as a skeleton.

SingleLiveEvent can be found here: https://github.com/googlesamples/android-architecture/blob/dev-todo-mvvm-live/todoapp/app/src/main/java/com/example/android/architecture/blueprints/todoapp/SingleLiveEvent.java