added adding instances

lib/pages/settings.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_hooks/flutter_hooks.dart';
 import 'package:flutter_mobx/flutter_mobx.dart';
 import 'package:provider/provider.dart';
 
@@ -77,12 +78,16 @@ class _AppearanceConfig extends StatelessWidget {
   }
 }
 
-class _AccountsConfig extends StatelessWidget {
+class _AccountsConfig extends HookWidget {
+  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey();
+
   @override
   Widget build(BuildContext context) {
     var theme = Theme.of(context);
+    var textFieldController = useTextEditingController();
 
     return Scaffold(
+      key: _scaffoldKey,
       appBar: AppBar(
         backgroundColor: theme.scaffoldBackgroundColor,
         shadowColor: Colors.transparent,
@@ -90,6 +95,48 @@ class _AccountsConfig extends StatelessWidget {
         title: Text('Accounts', style: theme.textTheme.headline6),
         centerTitle: true,
       ),
+      floatingActionButton: FloatingActionButton(
+        onPressed: () async {
+          await showDialog(
+            context: context,
+            builder: (ctx) => AlertDialog(
+              title: Text('Add instance'),
+              content: TextField(
+                controller: textFieldController,
+                decoration: InputDecoration(
+                  border: OutlineInputBorder(),
+                  labelText: 'Instance url',
+                ),
+              ),
+              actions: <Widget>[
+                FlatButton(
+                  child: Text('Add'),
+                  onPressed: () async {
+                    try {
+                      await context
+                          .read<AccountsStore>()
+                          .addInstance(textFieldController.text);
+                    } on Exception catch (err) {
+                      _scaffoldKey.currentState.showSnackBar(SnackBar(
+                        content: Text(err.toString()),
+                      ));
+                    }
+                    Navigator.of(context).pop();
+                  },
+                ),
+                FlatButton(
+                  child: Text('Cancel'),
+                  onPressed: () {
+                    Navigator.of(context).pop();
+                  },
+                )
+              ],
+            ),
+          );
+          textFieldController.clear();
+        },
+        child: Icon(Icons.add),
+      ),
       body: Observer(
         builder: (ctx) {
           var accountsStore = ctx.watch<AccountsStore>();

lib/stores/accounts_store.dart

@@ -139,13 +139,21 @@ abstract class _AccountsStore with Store {
     tokens[instanceUrl][userData.name] = token;
   }
 
-  /// adds a new instance with no accounts associated with it
+  /// adds a new instance with no accounts associated with it.
+  /// Additionally makes a test GET /site request to check if the instance exists
   @action
-  void addInstance(String instanceUrl) {
+  Future<void> addInstance(String instanceUrl) async {
     if (users.containsKey(instanceUrl)) {
       throw Exception('This instance has already been added');
     }
 
+    try {
+      await LemmyApi(instanceUrl).v1.getSite();
+      // ignore: avoid_catches_without_on_clauses
+    } catch (_) {
+      throw Exception('This instance seems to not exist');
+    }
+
     users[instanceUrl] = ObservableMap();
     tokens[instanceUrl] = ObservableMap();
   }

lib/stores/accounts_store.g.dart

@@ -93,6 +93,13 @@ mixin _$AccountsStore on _AccountsStore, Store {
         .run(() => super.addAccount(instanceUrl, usernameOrEmail, password));
   }
 
+  final _$addInstanceAsyncAction = AsyncAction('_AccountsStore.addInstance');
+
+  @override
+  Future<void> addInstance(String instanceUrl) {
+    return _$addInstanceAsyncAction.run(() => super.addInstance(instanceUrl));
+  }
+
   final _$_AccountsStoreActionController =
       ActionController(name: '_AccountsStore');
 
@@ -118,17 +125,6 @@ mixin _$AccountsStore on _AccountsStore, Store {
     }
   }
 
-  @override
-  void addInstance(String instanceUrl) {
-    final _$actionInfo = _$_AccountsStoreActionController.startAction(
-        name: '_AccountsStore.addInstance');
-    try {
-      return super.addInstance(instanceUrl);
-    } finally {
-      _$_AccountsStoreActionController.endAction(_$actionInfo);
-    }
-  }
-
   @override
   String toString() {
     return '''