Android中Kotlin实现FirebaseUI点击退出登录返回登录界面

Hey there! I see you're a Kotlin beginner working with FirebaseUI for Android, and you want to get users back to the sign-in interface once they tap the sign-out button. Let's adjust your code to make that work smoothly.

The Issue in Your Current Code #

Right now, your signOut call only handles the authentication sign-out, but it doesn't trigger navigation back to the sign-in screen. We need to add logic inside the addOnCompleteListener to launch the sign-in intent once the sign-out is successful.

Modified Code with Fix #

Here's your updated MainActivity with the sign-out redirection implemented:

class MainActivity : AppCompatActivity() { 
    private val RC_SIGN_IN = 123
    private val auth = FirebaseAuth.getInstance()
    
    // Choose authentication providers
    private val providers = arrayListOf(
        AuthUI.IdpConfig.EmailBuilder().build(),
        AuthUI.IdpConfig.PhoneBuilder().build(),
        AuthUI.IdpConfig.GoogleBuilder().build()
    )

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        signout.setOnClickListener { v -> 
            AuthUI.getInstance()
                .signOut(this)
                .addOnCompleteListener { task ->
                    if (task.isSuccessful) {
                        // Sign-out succeeded, launch the sign-in screen
                        val signInIntent = AuthUI.getInstance()
                            .createSignInIntentBuilder()
                            .setAvailableProviders(providers)
                            .build()
                        startActivity(signInIntent)
                        // Finish the current activity so users can't navigate back to MainActivity via back button
                        finish()
                    } else {
                        // Handle sign-out failure (e.g., show error message)
                        Toast.makeText(this, "Failed to sign out", Toast.LENGTH_SHORT).show()
                    }
                }
        }

        // Check if user is already signed in
        if (auth.currentUser == null) {
            // No user signed in, launch sign-in intent
            startActivityForResult(
                AuthUI.getInstance()
                    .createSignInIntentBuilder()
                    .setAvailableProviders(providers)
                    .build(), 
                RC_SIGN_IN
            )
        }
        // If user is signed in, do nothing (stay on MainActivity)
    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == RC_SIGN_IN) {
            val response = IdpResponse.fromResultIntent(data)
            if (resultCode == Activity.RESULT_OK) {
                // User signed in successfully, you can add logic here (e.g., welcome message)
                val user = FirebaseAuth.getInstance().currentUser
                Toast.makeText(this, "Welcome back, ${user?.displayName}!", Toast.LENGTH_SHORT).show()
            } else {
                // Sign-in failed, handle the error (e.g., show message)
                Toast.makeText(this, "Sign-in failed", Toast.LENGTH_SHORT).show()
            }
        }
    }
}

Key Changes Explained #

• Sign-Out Navigation: Inside addOnCompleteListener, we create and launch the FirebaseUI sign-in intent again once the sign-out is successful. We also call finish() to close MainActivity, so users can't press the back button to return to it without signing in again.
• Error Handling: Added basic error handling for both sign-out and sign-in failures using Toast messages to give clear feedback to the user.
• Cleaned Up User Check: Simplified the currentUser check to directly launch the sign-in intent if no user is signed in, making the code more readable.

Additional Tips #

• Double-check that your signout button is properly linked in your activity_main.xml layout (using android:id="@+id/signout").
• You can customize the sign-in screen further (like adding a logo or terms of service link) using FirebaseUI's builder methods such as setLogo() or setTosUrl().

内容的提问来源于stack exchange，提问作者Khagendra