improve login and logout

lib/appdata.dart

@@ -63,13 +63,16 @@ class _Appdata {
   Future<void> readData() async {
     final file = File("${App.dataPath}/account.json");
     if (file.existsSync()) {
-      account = Account.fromJson(jsonDecode(await file.readAsString()));
+      var json = jsonDecode(await file.readAsString());
+      if(json != null) {
+        account = Account.fromJson(json);
+      }
     }
     final settingsFile = File("${App.dataPath}/settings.json");
     if (settingsFile.existsSync()) {
       var json = jsonDecode(await settingsFile.readAsString());
       for (var key in json.keys) {
-        if(json[key] != null) {
+        if (json[key] != null) {
           settings[key] = json[key];
         }
       }

lib/components/button.dart

@@ -0,0 +1,96 @@
+import 'package:fluent_ui/fluent_ui.dart';
+import 'package:pixes/foundation/app.dart';
+
+abstract class BaseButton extends StatelessWidget {
+  const BaseButton({this.enabled = true, this.isLoading = false, super.key});
+
+  final bool enabled;
+
+  final bool isLoading;
+
+  Widget buildNormal(BuildContext context);
+
+  Widget buildLoading(BuildContext context);
+
+  Widget buildDisabled(BuildContext context);
+
+  @override
+  Widget build(BuildContext context) {
+    if (isLoading) {
+      return buildLoading(context);
+    } else if (enabled) {
+      return buildNormal(context);
+    } else {
+      return buildDisabled(context);
+    }
+  }
+}
+
+class FluentButton extends BaseButton {
+  const FluentButton({
+    required this.onPressed,
+    required this.child,
+    this.width,
+    super.enabled,
+    super.isLoading,
+    super.key,
+  });
+
+  final void Function() onPressed;
+
+  final Widget child;
+
+  final double? width;
+
+  static const _kFluentButtonPadding = 24;
+
+  @override
+  Widget buildNormal(BuildContext context) {
+    Widget child = this.child;
+    if (width != null) {
+      child = child.fixWidth(width! - _kFluentButtonPadding);
+    }
+    return FilledButton(
+      onPressed: onPressed,
+      child: child,
+    );
+  }
+
+  @override
+  Widget buildLoading(BuildContext context) {
+    Widget child = Center(
+      child: const ProgressRing(
+        strokeWidth: 1.6,
+      ).fixWidth(14).fixHeight(14),
+    );
+    if (width != null) {
+      child = child.fixWidth(width!);
+    }
+    return Container(
+      height: 26,
+      decoration: BoxDecoration(
+          color: FluentTheme.of(context).inactiveBackgroundColor,
+          borderRadius: BorderRadius.circular(4)),
+      child: child,
+    );
+  }
+
+  @override
+  Widget buildDisabled(BuildContext context) {
+    Widget child = Center(
+      child: this.child,
+    );
+    if (width != null) {
+      child = child.fixWidth(width!);
+    }
+    return Center(
+      child: Container(
+        height: 26,
+        decoration: BoxDecoration(
+            color: FluentTheme.of(context).inactiveBackgroundColor,
+            borderRadius: BorderRadius.circular(4)),
+        child: child,
+      ),
+    );
+  }
+}

lib/pages/login_page.dart

@@ -1,4 +1,5 @@
 import 'package:fluent_ui/fluent_ui.dart';
+import 'package:pixes/components/button.dart';
 import 'package:pixes/foundation/app.dart';
 import 'package:pixes/network/network.dart';
 import 'package:pixes/pages/webview_page.dart';
@@ -56,22 +57,11 @@ class _LoginPageState extends State<LoginPage> {
                       child: Column(
                         mainAxisSize: MainAxisSize.min,
                         children: [
-                          if (checked)
-                            FilledButton(
-                              onPressed: onContinue,
-                              child: Text("Continue".tl),
-                            )
-                          else
-                            Container(
-                              height: 28,
-                              width: 78,
-                              decoration: BoxDecoration(
-                                  color: FluentTheme.of(context)
-                                      .inactiveBackgroundColor,
-                                  borderRadius: BorderRadius.circular(4)),
-                              child: Center(
-                                child: Text("Continue".tl),
-                              ),
+                          FluentButton(
+                            onPressed: onContinue,
+                            enabled: checked, 
+                            width: 96,
+                            child: Text("Continue".tl),
                             ),
                           const SizedBox(
                             height: 16,

lib/pages/settings_page.dart

@@ -88,6 +88,7 @@ class _SettingsPageState extends State<SettingsPage> {
                         child: Text('Continue'.tl),
                         onPressed: () {
                           appdata.account = null;
+                          appdata.writeData();
                           App.rootNavigatorKey.currentState!.pushAndRemoveUntil(
                               AppPageRoute(
                                   builder: (context) => const MainPage()),