Android Studio (Kotlin) - User has to log back into app every time app is closed

问题

So i have a RegisterActivity and a MapsActivity. When a new user opens the app, they will be on the RegisterActivity and sign up. Once they sign up, my app creates an Intent and sends them to the MapsActivity

The problem is whenever the user closes the app, they have to login/register again.

I want the the app to be able to open back to the MapsActivity since the user has not signed out yet

---

Here's my attempt:

i put an <intent-filter> in both RegisterActivity and MapsActivity because i think both should both be the main launchers depending if a user is logged in or not right?

• If they aren't logged in, then the main launcher should be RegisterActivity
• If they are logged in, then the main launcher should be MapsActivity

AndroidManifest.xml

<application
    <activity android:name=".MapsActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>

    <activity android:name=".RegisterActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN"/>
        <action android:name="android.intent.action.VIEW"/>
        <category android:name="android.intent.category.LAUNCHER"/>
    </intent-filter>
    </activity>

    <activity android:name=".LoginActivity">
    </activity>

</application>

MapsActivity.kt

public override fun onStart() {
    super.onStart()
    // Check if user is signed in (non-null) and update UI accordingly.
    val currentUser = FirebaseAuth.getInstance().currentUser
    if(currentUser == null){
        Log.d(TAG, "User is not logged in")
        val intent = Intent(this, LoginActivity::class.java)
        intent.flags = Intent.FLAG_ACTIVITY_CLEAR_TASK.or(Intent.FLAG_ACTIVITY_NEW_TASK)
        startActivity(intent)
    }else {
        Log.d(TAG, "User is logged in")
    }
}

回答1:

The simplest way to achieve this is to use a listener. Let's assume you have two activities, the LoginActivity and the MainActivity. The listener that can be created in the LoginActivity should look like this:

val authStateListener = FirebaseAuth.AuthStateListener { firebaseAuth ->
    val firebaseUser = firebaseAuth.currentUser
    if (firebaseUser != null) {
        val intent = Intent(this, MainActivity::class.java)
        startActivity(intent)
        finish()
    }
}

This basically means that if the user is logged in, skip the LoginActivity and go to the MainActivity.

Instantiate the FirebaseAuth object:

val firebaseAuth = FirebaseAuth.getInstance()

And start listening for changes in your onStart() method like this:

override fun onStart() {
    super.onStart()
    firebaseAuth!!.addAuthStateListener(this.authStateListener!!)
}

In the MainActivity, you should do the same thing:

val authStateListener = FirebaseAuth.AuthStateListener { firebaseAuth ->
    val firebaseUser = firebaseAuth.currentUser
    if (firebaseUser == null) {
        val intent = Intent(this, LoginActivity::class.java)
        startActivity(intent)
    }
}

Which basically means that if the user is not logged in, skip the MainActivity and go to the LoginActivity. In this activity you should do the same thing as in the LoginActivity, you should start listening for changes in the onStart().

In both activities, don't forget to remove the listener in the moment in which is not needed anymore. So add the following line of code in your onStop() method:

override fun onStop() {
    super.onStop()
    firebaseAuth!!.removeAuthStateListener(this.authStateListener!!)
}

回答2:

I have developer a similar app and I simply use a splash screen that checks if the users is logged or not and then open the right screen. The splash doesn't need to be to complex: in fact you can even avoid to set a view and just check whatever you want. This article explains it very clearly.

Remember to call finish() on the splash activity after launching the right one.

来源：https://stackoverflow.com/questions/54046250/android-studio-kotlin-user-has-to-log-back-into-app-every-time-app-is-closed