自定义 RichTextBlock 引发异常 "Element is already the child of another element"

Question

我使用 FlipView 控件，在 ItemTemplate 内部我有自定义 RichTextBlock，其中 Elements 属性创建为 Run 元素的集合。它有效，但是，有时我会收到异常 “WinRT 信息：元素已经是另一个元素的子元素。” 我真的不明白为什么。

有人可以解释一下为什么会这样吗？

示例 - http://1drv.ms/1yZM8a5

模型（包含测试数据）

public class Page
{
    public Page()
    {
        Data = new List<Run>();
        Data.Add(new Run { Text = "1" });
        Data.Add(new Run { Text = "2" });
        Data.Add(new Run { Text = "3" });
        Data.Add(new Run { Text = "4" });
        Data.Add(new Run { Text = "5" });
    }
    public IList<Run> Data { get; set; }
}

ViewModel（FlipView 页面集合）

public ObservableCollection<Page> Pages { get; set; }

// test data
Pages = new ObservableCollection<Page>();
Pages.Add(new Page()); // etc

XAML

<FlipView ItemsSource="{Binding Pages}">
    <FlipView.ItemTemplate>
        <DataTemplate>
            <local:ExtendedRichTextBlock Elements="{Binding Data}" />
        </DataTemplate>
    </FlipView.ItemTemplate>
</FlipView>

ExtendedRichTextBlock

Elements 是依赖项属性并在此处捕获更改：

private static void OnElementsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    ExtendedRichTextBlock sender = d as ExtendedRichTextBlock;

    if (sender != null)
    {
        sender.Content.Blocks.Clear();

        var x = e.NewValue as IList<Run>;
                
        if (x != null)
        {
            foreach (var item in x)
            {
                var p = new Paragraph();
                p.Inlines.Add(item);    // WinRT information: Element is already the child of another element.

                sender.Content.Blocks.Add(p);
            }
        }
    }
}

结论

我在 chat.

中与 Romasz 讨论的简短结论

Every time the event is fired you are clearing content and then populating it reusing Run elements. In the behind it may be quite complex - maybe some animations, transitions and so on, I'm also not sure if this is not made asynchronously - if so there may be situation when elements still have a parent and you try to reuse it. Consider better thing, populating every time with UI elements it's not a good idea - make your datatemlate with those UI elements and bind their content to some kind of collection.

因此必须在 OnElementsChanged 中动态创建所有元素。

Answer 1

似乎您的程序有时会尝试使运行元素成为另一个控件的 child，而它已经具有 parent UI 个元素只能有一个 parent。

在这种情况下，请考虑对您的应用进行少量更改：

private static void OnElementsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    ExtendedRichTextBlock sender = d as ExtendedRichTextBlock;

    if (sender != null)
    {
        sender.Content.Blocks.Clear();

        var x = e.NewValue as IList<string>;

        if (x != null)
        {
            foreach (var item in x)
            {
                var p = new Paragraph();
                p.Inlines.Add(new Run { Text = item });    // WinRT information: Element is already the child of another element.
                sender.Content.Blocks.Add(p);
            }
        }
    }
}

当然要完成这项工作，您需要将所有 IList<Run> 更改为 IList<string>。

这将确保每个运行元素都是没有 parent.

的新元素

自定义 RichTextBlock 引发异常 "Element is already the child of another element"

Custom RichTextBlock raise exception "Element is already the child of another element"

c#

xaml

windows-8.1

windows-phone-8.1