Add more docs and cleanup

Signed-off-by: Alex Saveau <[email protected]>

Author: SUPERCILEX

app/src/main/java/com/firebase/uidemo/auth/AuthUiActivity.java

@@ -42,9 +42,7 @@
 import com.google.android.gms.tasks.OnCompleteListener;
 import com.google.android.gms.tasks.Task;
 import com.google.firebase.auth.AuthResult;
-import com.google.firebase.auth.EmailAuthProvider;
 import com.google.firebase.auth.FirebaseAuth;
-import com.google.firebase.auth.GoogleAuthProvider;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -172,16 +170,7 @@ public void signIn(View view) {
 
     @OnClick(R.id.sign_in_silent)
     public void silentSignIn(View view) {
-        List<IdpConfig> providers = new ArrayList<>();
-        for (IdpConfig config : getSelectedProviders()) {
-            String provider = config.getProviderId();
-            if (provider.equals(EmailAuthProvider.PROVIDER_ID)
-                    || provider.equals(GoogleAuthProvider.PROVIDER_ID)) {
-                providers.add(config);
-            }
-        }
-
-        AuthUI.getInstance().silentSignIn(this, providers)
+        AuthUI.getInstance().silentSignIn(this, getSelectedProviders())
                 .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                     @Override
                     public void onComplete(@NonNull Task<AuthResult> task) {

auth/README.md

@@ -33,8 +33,9 @@ and [Web](https://github.com/firebase/firebaseui-web/).
 1. [Configuration](#configuration)
    1. [Provider config](#identity-provider-configuration)
 1. [Usage instructions](#using-firebaseui-for-authentication)
-   1. [Sign in](#sign-in)
+   1. [AuthUI sign-in](#authui-sign-in)
    1. [Handling responses](#handling-the-sign-in-response)
+   1. [Silent sign-in](#silent-sign-in)
    1. [Sign out](#sign-out)
    1. [Account deletion](#deleting-accounts)
    1. [Auth flow chart](#authentication-flow-chart)
@@ -169,7 +170,7 @@ If an alternative app instance is required, call
 `AuthUI.getInstance(app)` instead, passing the appropriate `FirebaseApp`
 instance.
 
-### Sign in
+### AuthUI sign-in
 
 If a user is not currently signed in, as can be determined by checking
 `auth.getCurrentUser() != null` (where `auth` is the `FirebaseAuth` instance
@@ -352,7 +353,7 @@ protected void onActivityResult(int requestCode, int resultCode, Intent data) {
                 showSnackbar(R.string.no_internet_connection);
                 return;
             }
-        
+
             showSnackbar(R.string.unknown_error);
             Log.e(TAG, "Sign-in error: ", response.getError());
         }
@@ -399,6 +400,40 @@ if (metadata.getCreationTimestamp() == metadata.getLastSignInTimestamp()) {
 }
 ```
 
+### Silent sign-in
+
+If a user is not currently signed in, then a silent sign-in process can be started first before
+displaying any UI to provide a seamless experience. Silent sign-in uses saved Smart Lock credentials
+and returns a successful `Task` only if the user has been fully signed in with Firebase.
+
+Here's an example of how you would use silent sign-in paired with anonymous users to get your users
+up and running as fast as possible:
+
+```java
+List<IdpConfig> providers = getSelectedProviders();
+AuthUI.getInstance().silentSignIn(this, providers)
+        .continueWithTask(new Continuation<AuthResult, Task<AuthResult>>() {
+    @Override
+    public Task<AuthResult> then(@NonNull Task<AuthResult> task) {
+        if (task.isSuccessful()) {
+            return task;
+        } else {
+            // Ignore any exceptions since we don't care about credential fetch errors.
+            return FirebaseAuth.getInstance().signInAnonymously();
+        }
+    }
+}).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
+    @Override
+    public void onComplete(@NonNull Task<AuthResult> task) {
+        if (task.isSuccessful()) {
+            // Signed in! Start loading data
+        } else {
+            // Uh oh, show error message
+        }
+    }
+});
+```
+
 ### Sign out
 
 With the integrations provided by AuthUI, signing out a user is a multi-stage process:

auth/src/main/java/com/firebase/ui/auth/AuthUI.java

@@ -295,6 +295,10 @@ public Task<AuthResult> silentSignIn(@NonNull Context context,
             }
         }
 
+        if (configs.isEmpty()) {
+            throw new IllegalArgumentException("No supported providers were supplied.");
+        }
+
         final Context appContext = context.getApplicationContext();
         final IdpConfig google =
                 ProviderUtils.getConfigFromIdps(configs, GoogleAuthProvider.PROVIDER_ID);