Question

我在班级

中创建了可观察的集合

public ObservableCollection<NewsTags> NewsTagsList { get; private set; }

public RelayCommand RefreshNewsTags
{
    get
    {
        return _refreshNewsTagsCommand ?? (
            _refreshNewsTagsCommand = new RelayCommand(
                async () => {
                    var list = await _newsTagsService.GetAllAsync(1, false);
                    foreach (var item in list)
                    {
                        NewsTagsList.Add(item);
                    }
                }
         ));
    }
}

并致电自定义控件

<tagsListSelector:BoxSelector Items="{Binding NewsTagsList}" />

和boxselector.cs

public partial class BoxSelector : ContentView
{
    public BoxSelector()
    {
        InitializeComponent();
    }

    public static readonly BindableProperty ItemsProperty =
       BindableProperty.Create<BoxSelector, IEnumerable>(
           view => view.ItemsSource,
           null,
           propertyChanged: (bindableObject, oldValue, newValue) => {

               ((BoxSelector)bindableObject).ItemsSourceChanged(bindableObject, oldValue, newValue);
           }
       );

    private void ItemsSourceChanged(BindableObject bindableObject, IEnumerable oldvalue, IEnumerable newvalue)
    {
        boxSelectorGrid.Children.Clear();

        foreach (object obj in newvalue)
        {
            boxSelectorGrid.Children.Add(new Label { Text="LOL", TextColor= Color.FromHex("#000")});
        }
    }

但没有变化。 p.s in newslist.cs NewsTagsList.Count == 10但在BoxSelector == 0

我做错了什么？

Answer 1

在ItemsSourceChanged方法中，如果newValue的类型为INotifyCollectionChanged，则需要连接CollectionChanged事件，并在CollectionChanged代码内部执行集合更改时要执行的操作。如果类型为INotifyCollectionChanged，您还需要取消订阅oldValue上的事件。

这样的事情：

        private void ItemsSourceChanged(BindableObject bindableObject, IEnumerable oldvalue, IEnumerable newvalue)
    {
        var incc = oldvalue as INotifyCollectionChanged;
        if (incc != null)
        {
            incc.CollectionChanged -= Incc_CollectionChanged;
        }
        incc = newvalue as INotifyCollectionChanged;
        if (incc != null)
        {
            incc.CollectionChanged += Incc_CollectionChanged;
        }
        boxSelectorGrid.Children.Clear();

        foreach (object obj in newvalue)
        {
            boxSelectorGrid.Children.Add(new Label { Text = "LOL", TextColor = Color.FromHex("#000") });
        }
    }

    private void Incc_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                // handle Added rows
                break;
            case NotifyCollectionChangedAction.Remove:
                // handle deleting rows
                break;
            case NotifyCollectionChangedAction.Move:
                // handle moving rows
                break;
            case NotifyCollectionChangedAction.Replace:
                // handle replacing rows
                break;
            case NotifyCollectionChangedAction.Reset:
                // reload everything
                break;
        }
    }

为什么不在绑定XAML中更改数据？

1 个答案: