第二次刷新分組listview崩潰

Question

我有一個分組Xamarin ListView，並發現它更新ListView中的值麻煩。

ViewModel;

public class MainViewModel 
{ 
    private ObservableCollection<ObservableGroupCollection<string, TaskItem>> _userTasksGrouped; 
    public ObservableCollection<ObservableGroupCollection<string, TaskItem>> UserTasksGrouped 
    { 
     get => _userTasksGrouped; 
     set 
     { 
      _userTasksGrouped = value; 
      OnPropertyChanged(); 
     } 
    } 

    private void PopulateMyTasks() 
    { 
     UserTasks.Clear(); 
     foreach (var task in MyTasks) 
     { 
      UserTasks.Add(new TaskItem(task)); 
     } 
     DoTaskGrouping(); 
    } 

    private void DoTaskGrouping() 
    { 
     UserTasksGrouped.Clear(); 
     var groupedData = 
      UserTasks 
       .OrderBy(ut => ut.Name) 
       .GroupBy(ut => ut.StateEnum.ToString()) 
       .Select(ut => new ObservableGroupCollection<string, TaskItem>(ut)) 
       .ToList(); 
     foreach (var group in groupedData) 
      UserTasksGrouped.Add(group); 
    } 

    public void UpdateTaskItem(TaskChanged taskChanged) 
    { 
     // update listing 
     var usertask = UserTasksGrouped.First(utg => utg.Any(ut => ut.Task.Id == taskChanged.Task.Id)) 
      .First(t => t.Task.Id == taskChanged.Task.Id); 
     if (usertask != null) 
     { 
      usertask.Task = taskChanged.Task; 
     } 
     else 
     { 
      // something else 
     } 
     DoTaskGrouping(); 
    } 

    public MainViewModel() 
    { 
     UserTasks = new ObservableCollection<TaskItem>(); 
     UserTasksGrouped = new ObservableCollection<ObservableGroupCollection<string, TaskItem>>(); 
    } 
} 

XAML;

<ListView 
    IsGroupingEnabled="true" 
    ItemsSource="{Binding UserTasksGrouped}" 
    GroupDisplayBinding="{Binding Key}" 
    GroupShortNameBinding="{Binding Key}"> 

    <ListView.ItemTemplate> 
     <DataTemplate> 
      <ViewCell> 
       <ViewCell.View> 
        <Grid> 
         <Grid.RowDefinitions> 
          <RowDefinition Height="Auto" /> 
          <RowDefinition Height="Auto" /> 
         </Grid.RowDefinitions> 
         <Grid.ColumnDefinitions> 
          <ColumnDefinition Width="Auto" /> 
          <ColumnDefinition Width="Auto" /> 
          <ColumnDefinition Width="50*" /> 
          <ColumnDefinition Width="Auto" /> 
         </Grid.ColumnDefinitions> 

         <BoxView 
          Grid.Row="0" Grid.RowSpan="2" 
          Grid.Column="0" Grid.ColumnSpan="2" 
          MinimumHeightRequest="16" 
          MinimumWidthRequest="16" 
          Margin="0" 
          Color="{Binding StatusColour}" /> 

         <Label 
          Grid.Row="0" Grid.Column="2" 
          Text="{Binding Name}" 
          Style="{StaticResource LabelStyle}" 
          WidthRequest="200" /> 
        </Grid> 
       </ViewCell.View> 
      </ViewCell> 
     </DataTemplate> 
    </ListView.ItemTemplate> 
</ListView> 

任務項目：

public class TaskItem : INotifyPropertyChanged 
{ 
    private MyTask _task; 
    public MyTask Task 
    { 
     get => _task; 
     set 
     { 
      _task = value; 
      Name = value.Name; 
      OnPropertyChanged(); 
     } 
    } 

    private string _name; 
    public string Name 
    { 
     get => _name; 
     set 
     { 
      _name = value; 
      OnPropertyChanged(); 
     } 
    } 

    public string StatusColour => "Green" 
} 

當我打電話DoTaskGrouping（）第二次強制刷新的應用程序與UnhandledException崩潰的問題。我設法跟蹤到一個「具有相同密鑰的項目已被添加」的錯誤，所以我添加了ViewCell.View，認爲它可能會解決問題。請幫忙，我有幾個問題;

1. 我該如何解決錯誤「已經添加了具有相同密鑰的項目」併成功刷新了我的分組列表。
2. 可觀察集合中的可觀察集合是否自動更新。這意味着如果屬性或它們按變化分組，那麼分組也是如此？意味着物品可以在組之間移動？
3. 我的方法是從MVVM的角度來聽的嗎？ TaskItem可以做清理。

Answer 1

修正通過從MainViewModel

public ObservableCollection<ObservableGroupCollection<string, TaskItem>> UserTasksGrouped 

DoTaskGrouping去除（）每次構建集合重新;

UserTasksGrouped = new ObservableCollection<ObservableGroupCollection<string, TaskItem>>(groupedData);