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;

 

 

    public class Task : System.ComponentModel.INotifyPropertyChanged, IEditableObject
    {
        // The Task class implements INotifyPropertyChanged and IEditableObject 
        // so that the datagrid can properly respond to changes to the 
        // data collection and edits made in the DataGrid.

        // Private task data.
        private string m_ProjectName = string.Empty;
        private string m_TaskName = string.Empty;
        private DateTime m_DueDate = DateTime.Now;
        private bool m_Complete = false;
        private string m_Notes = string.Empty;

        // Data for undoing canceled edits.
        private Task temp_Task = null;
        private bool m_Editing = false;

        public double Area { get; set; }

        // Public properties.
        [Display(Name = "公司")]
        public string ProjectName
        {
            get { return this.m_ProjectName; }
            set
            {
                if (value != this.m_ProjectName)
                {
                    this.m_ProjectName = value;
                    NotifyPropertyChanged("ProjectName");
                }
            }
        }

        [Display(Name = "项目")]
        public TaskProject Project
        {
            get;
            set;
        }

        [Display(Name = "Task")]
        public string TaskName
        {
            get { return this.m_TaskName; }
            set
            {
                if (value != this.m_TaskName)
                {
                    this.m_TaskName = value;
                    NotifyPropertyChanged("TaskName");
                }
            }
        }

        [Display(Name = "Due Date")]
        public DateTime DueDate
        {
            get { return this.m_DueDate; }
            set
            {
                if (value != this.m_DueDate)
                {
                    this.m_DueDate = value;
                    NotifyPropertyChanged("DueDate");
                }
            }
        }

        public bool Complete
        {
            get { return this.m_Complete; }
            set
            {
                if (value != this.m_Complete)
                {
                    this.m_Complete = value;
                    NotifyPropertyChanged("Complete");
                }
            }
        }

        public string Notes
        {
            get { return this.m_Notes; }
            set
            {
                if (value != this.m_Notes)
                {
                    this.m_Notes = value;
                    NotifyPropertyChanged("Notes");
                }
            }
        }

        // Implement INotifyPropertyChanged interface.
        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        // Implement IEditableObject interface.
        public void BeginEdit()
        {
            if (m_Editing == false)
            {
                temp_Task = this.MemberwiseClone() as Task;
                m_Editing = true;
            }
        }

        public void CancelEdit()
        {
            if (m_Editing == true)
            {
                this.ProjectName = temp_Task.ProjectName;
                this.TaskName = temp_Task.TaskName;
                this.DueDate = temp_Task.DueDate;
                this.Complete = temp_Task.Complete;
                this.Notes = temp_Task.Notes;
                m_Editing = false;
            }
        }

        public void EndEdit()
        {
            if (m_Editing == true)
            {
                temp_Task = null;
                m_Editing = false;
            }
        }
    }

 

public class ProjectConverter : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return (value as TaskProject).ProjectName;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return 0;
        }

    }

 

 

public class TaskProject : IComparable, IComparable<TaskProject>
    {
        public int ProjectId { get; set; }
        public string ProjectName { get; set; }

        public override string ToString()
        {
            return this.ProjectName;
        }

        #region IComparable 成员

        public int CompareTo(object obj)
        {
            return this.CompareTo(obj as TaskProject);
        }

        #endregion

        #region IComparable<TaskProject> 成员

        public int CompareTo(TaskProject other)
        {
            if (other == null)
            {
                return -1;
            }
            return this.ProjectId - other.ProjectId;
        }

        #endregion
    }