added delete button

fixed exception when owner attribute is null

lib/components/TaskTile.dart

@@ -8,9 +8,10 @@ import 'package:vikunja_app/pages/task/edit_task.dart';
 
 class TaskTile extends StatefulWidget {
   final Task task;
+  final Function onEdit;
 
   const TaskTile(
-      {Key key, @required this.task})
+      {Key key, @required this.task, this.onEdit})
       : assert(task != null),
         super(key: key);
 /*
@@ -68,7 +69,10 @@ class TaskTileState extends State<TaskTile> {
                 MaterialPageRoute(
                     builder: (context) => TaskEditPage(
                       task: _currentTask,
-                    ))).whenComplete(() => setState((){}));
+                    ))).whenComplete(() {
+                      //setState((){});
+                      widget.onEdit();
+                    });
           }),
       onChanged: _change,
     );

lib/models/list.dart

@@ -20,7 +20,7 @@ class TaskList {
 
   TaskList.fromJson(Map<String, dynamic> json)
       : id = json['id'],
-        owner = User.fromJson(json['owner']),
+        owner = json['owner'] == null ? null :  User.fromJson(json['owner']),
         description = json['description'],
         title = json['title'],
         updated = DateTime.parse(json['updated']),

lib/models/namespace.dart

@@ -21,7 +21,7 @@ class Namespace {
         id = json['id'],
         created = DateTime.parse(json['created']),
         updated = DateTime.parse(json['updated']),
-        owner = User.fromJson(json['owner']);
+        owner = json['owner'] == null ? null : User.fromJson(json['owner']);
 
   toJSON() => {
         "created": created?.toIso8601String(),

lib/models/task.dart

@@ -34,7 +34,7 @@ class Task {
         description = json['description'],
         title = json['title'],
         done = json['done'],
-        owner = User.fromJson(json['created_by']);
+        owner = json['created_by'] == null ? null : User.fromJson(json['created_by']);
 
   toJSON() => {
         'id': id,

lib/pages/list/list.dart

@@ -50,7 +50,10 @@ class _ListPageState extends State<ListPage> {
                     MaterialPageRoute(
                         builder: (context) => ListEditPage(
                               list: _list,
-                            ))).whenComplete(() {_loadList(); setState(() {});})
+                            ))).whenComplete(() {
+                              _loadList();
+                              setState(() {});
+                            })
                 )
           ],
         ),
@@ -82,7 +85,7 @@ class _ListPageState extends State<ListPage> {
   TaskTile _buildTile(Task task) {
     // key: UniqueKey() seems like a weird workaround to fix the loading issue
     // is there a better way?
-    return TaskTile(key: UniqueKey(), task: task);
+    return TaskTile(key: UniqueKey(), task: task,onEdit: () => _loadList());
   }
 
   Future<void> _loadList() {

lib/pages/task/edit_task.dart

@@ -140,6 +140,13 @@ class _TaskEditPageState extends State<TaskEditPage> {
                                 ? CircularProgressIndicator()
                                 : VikunjaButtonText('Save'),
                           ))),
+                  Builder(
+                      builder: (context) => Padding(
+                          padding: EdgeInsets.symmetric(vertical: 10.0),
+                          child: FancyButton(
+                            onPressed: () {_deleteTask(context);},
+                            child:  VikunjaButtonText('Delete'),
+                          ))),
                 ]),
           ),
         ),
@@ -169,6 +176,13 @@ class _TaskEditPageState extends State<TaskEditPage> {
       });
   }
 
+  _deleteTask(BuildContext context) async {
+    await VikunjaGlobal.of(context).taskService.delete(widget.task.id).then(
+            (value) {
+              Navigator.pop(context);
+            });
+  }
+
   _saveTask(BuildContext context) async {
     setState(() => _loading = true);
     Task updatedTask = widget.task;