login: implement login on enter

lib/login_page.dart

@@ -18,8 +18,11 @@ class _LoginPageState extends State<LoginPage> {
   final TextEditingController _emailController = TextEditingController();
   final TextEditingController _passwordController = TextEditingController();
 
+  final _formKey = GlobalKey<FormState>();
+
   final StorageHelper _storageHelper = StorageHelper();
   String? _error;
+  bool loggingIn = false;
 
   @override
   void initState() {
@@ -83,47 +86,76 @@ class _LoginPageState extends State<LoginPage> {
     );
   }
 
+  String? validateNotEmpty(String? content) {
+    if (content == null || content.isEmpty) {
+      return "Do not leave this field empty";
+    }
+    return null;
+  }
+
+  void handleLoginPressed() async {
+    if (loggingIn) return;
+
+    loggingIn = true;
+    if (_formKey.currentState!.validate()) {
+      await _login(
+        _urlController.text,
+        _emailController.text,
+        _passwordController.text,
+      );
+    }
+    loggingIn = false;
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(title: Text('Login')),
       body: Padding(
         padding: const EdgeInsets.all(16.0),
+        child: Form(
+          key: _formKey,
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
-            TextField(
+              TextFormField(
                 controller: _urlController,
+                validator: validateNotEmpty,
                 decoration: InputDecoration(labelText: 'Url'),
+                textInputAction: TextInputAction.next,
               ),
-            TextField(
+              TextFormField(
                 controller: _emailController,
+                validator: validateNotEmpty,
+                autofocus: true,
                 decoration: InputDecoration(labelText: 'Email'),
+                textInputAction: TextInputAction.next,
               ),
-            TextField(
+              TextFormField(
                 controller: _passwordController,
+                validator: validateNotEmpty,
+                // focusNode: _passwordFocusNode,
                 decoration: InputDecoration(labelText: 'Password'),
                 obscureText: true,
+                textInputAction: TextInputAction
+                    .next, // with submit or go, onFieldSubmitted is not called
+                onFieldSubmitted: (_) => handleLoginPressed(),
+              ),
+              // ),
+              SizedBox(height: 5),
+              ElevatedButton(
+                onPressed: loggingIn ? null : handleLoginPressed,
+                child: Text('Login'),
               ),
               if (_error != null)
                 Padding(
                   padding: const EdgeInsets.only(top: 8.0),
                   child: Text(_error!, style: TextStyle(color: Colors.red)),
                 ),
-            SizedBox(height: 16),
-            ElevatedButton(
-              onPressed: () {
-                _login(
-                  _urlController.text,
-                  _emailController.text,
-                  _passwordController.text,
-                );
-              },
-              child: Text('Login'),
-            ),
             ],
           ),
         ),
+      ),
     );
   }
 }