DataGrid排序错误：必须至少有一个对象实现

当DataGrid使用对象进行了分组时候，该对象类型必须实现 IComparable 接口，否则出错：必须至少有一个对象实现。

 

代码如下：

 

            ObservableCollection<TaskProject> list1 = new ObservableCollection<TaskProject>();
            for (int i = 1; i <= 2; i++)
            {
                list1.Add(new TaskProject()
                {
                    ProjectId = i,
                    ProjectName = "Project " + i.ToString(),
                });
            }
            list1.Add(new TaskProject() { ProjectId = 1, ProjectName = "Project 1" });
            this.dataGrid2.ItemsSource = new PagedCollectionView(list1);

            ObservableCollection<Task> taskList = new ObservableCollection<Task>();
            // Generate some task data and add it to the task list.
            for (int i = 1; i <= 100; i++)
            {
                taskList.Add(new Task()
                {
                    Area = i / 3D,
                    ProjectName = "公司 " + ((i % 5) + 1).ToString(),
                    TaskName = "Task " + i.ToString(),
                    Project = list1[i % list1.Count],
                    DueDate = DateTime.Now.AddDays(i),
                    Complete = (i % 2 == 0),
                    Notes = "Task " + i.ToString() + " is due on "
                          + DateTime.Now.AddDays(i) + ". Lorum ipsum..."
                });
            }

            PagedCollectionView taskListView = new PagedCollectionView(taskList);
            taskListView.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(taskListView_CollectionChanged);
            this.dataGrid1.ItemsSource = taskListView;


            if (taskListView.CanGroup == true)
            {
                PropertyGroupDescription group = new PropertyGroupDescription("Project");
                group.Converter = new ProjectConverter();
                taskListView.GroupDescriptions.Add(group);
                // Then group by Complete status.
                taskListView.GroupDescriptions.Add(new PropertyGroupDescription("Complete"));
            }
            if (taskListView.CanSort == true)
            {
                // By default, sort by ProjectName.
                taskListView.SortDescriptions.Add(new SortDescription("ProjectName", ListSortDirection.Ascending));
            }

            dataPager1.Source = taskListView;