如何从 WPF 中的可视化树分离

Question

我正在尝试从 InlineUIContainer 中正确删除 UIElement 以便在另一个面板中使用它，但程序一直崩溃并显示此消息 "Specified Visual is already a child of another Visual or the root of a CompositionTarget."。

我创建了一个小应用程序来说明我的痛苦。在这个节目中，一旦 Randy the button 被他的女朋友 killed\deleted，他仍然没有与他的 parent 分开，我发现他的女朋友是 UIElementIsland。然后任何将 Randy 添加为 child 的任何其他尝试都会使应用程序崩溃（The Apocalypse Button 证明了我的观点 :)）。你可以点击查看Randy的parents before\after 删除Randy会发现他一直在UIElementIsland下作为一个child，如果他脱离整个problem\apocalypse应该避免。

这是一个有趣的应用程序，即使只是为了好玩，也请复制并编译！任何 help\ideas 将不胜感激！

C# 部分：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace DetachingfromUIElementIsland
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        int t = 0;

        static string[] info = new string[] { "Okay, Lets have a look...", "Checking."
            , "Checking..", "Checking...", "Seen it!"  };

        /// <summary>
        /// Makes the App fancy :)
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void timer_Tick(object sender, EventArgs e)
        {
            display.Text = info[t];

            if (t == 0)
                timer.Interval = new TimeSpan(0, 0, 0, 0, 300);

            t++;
            if (t >= 4)
            {
                t = 0;
                timer.Stop();
                display.Text = GetRandysParent();
            }
        }

        private void deleteRandy_Click(object sender, RoutedEventArgs e)
        {
            // This might be the bug.
            // Maybe there's a better way to do this.
            // If there was a VisualTreeHelper.Remove().
            randy_container.Child = null;

            display.Text = "Haha! I just killed Randy!!! He'll never get the chance"
                + "\n to hurt another woman again!";
            display.Background = Brushes.Violet;
            end.Visibility = System.Windows.Visibility.Visible;
        }

        DispatcherTimer timer = null;

        /// <summary>
        /// Check if Randy is Still attached to UIElementIsland
        /// </summary>
        /// <returns></returns>
        private string GetRandysParent()
        {
            // Check the visual tree to see if randy is removed properly
            DependencyObject dp = VisualTreeHelper.GetParent(randy);
            string text = string.Empty;
            if (dp != null)
            {
                display.Background = Brushes.LightGreen;
                text = "Randy's Dad is Mr " + dp.ToString();
            }

            else
            {
                // This should be what you'll get when the code works properly
                display.Background = Brushes.Red;
                text = "Weird...Randy doesn't seem to have a dad...";
            }
            return text;
        }

        private void findParents_Click(object sender, RoutedEventArgs e)
        {  
            display.Background = Brushes.Yellow;

            // Creates a timer to display some fancy stuff
            // and then Randy's.
            // Just to prove to you that this button actually works.
            timer = new DispatcherTimer();
            timer.Start();
            timer.Tick += timer_Tick;
            timer.Interval = new TimeSpan(0, 0, 0, 0, 700);
        }

        private void randy_Click(object sender, RoutedEventArgs e)
        {
            // Get Randy to introduce himself
            display.Text = "Hi, I'm Randy!!!";
            display.Background = Brushes.Orange;
        }

        private void end_Click(object sender, RoutedEventArgs e)
        {
            // If randy is removed properly, this would not crash the application.
            StackPanel s = new StackPanel();
            s.Children.Add(randy);
            // CRASH!!!
        }
    }
}

XAML:

<Window x:Class="DetachingfromUIElementIsland.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <FlowDocument IsEnabled="True" x:Name="document">
        <Paragraph>
            <InlineUIContainer x:Name="randy_container">
                <!--Meet Randy-->
                <Button Name="randy" Content="I am a Randy, the button" Click="randy_Click" ToolTip="Meet Randy"/>
            </InlineUIContainer>
            <LineBreak/>
            <LineBreak/>
            <InlineUIContainer x:Name="container2">
                <!--Meet Randy's Ex Girlfriend-->
            <Button Name="deleteRandy" Content="Randy dumped me for another girl :(, click me to delete him" Click="deleteRandy_Click" ToolTip="Meet Randy's Ex Girlfriend"/>
            </InlineUIContainer>
            <LineBreak/>
            <LineBreak/>
            <InlineUIContainer x:Name="container3">
                <!--He can help you find Randy's Parents-->
            <Button Name="findParents" Content="Click me to find randy's parents" Click="findParents_Click" ToolTip="He can help you find Randy's Parents"/>
            </InlineUIContainer>
            <LineBreak/>
            <LineBreak/>
            <InlineUIContainer x:Name="Apocalypse">
                <!--End the world, Crash the application-->
                <Button x:Name="end" Content="Avenge Randy's Death" Click="end_Click" ToolTip="End the world, Crash the application" Visibility="Hidden"/>
            </InlineUIContainer>
        </Paragraph>
        <Paragraph>
            <InlineUIContainer>
                <TextBlock x:Name="display" Foreground="Black"/>  
            </InlineUIContainer>
        </Paragraph>
    </FlowDocument>
</Window>

整个代码本应比这更短，但我对其进行了调味以使其变得有趣。希望我能让某人的一天变亮一点。但是，请帮帮我 :).

答案： 从 Randy 的 InlineUIContainer 推导出如下：

    public class DerivedInlineUIContainer : InlineUIContainer
    {   
        public DerivedInlineUIContainer()
        {

        }

        public void RemoveFromLogicalTree(FrameworkElement f)
        {
            this.RemoveLogicalChild(f);
        }
    }

这一次你可以正确地杀死Randy，并将他添加到UIElement天堂（StackPanel）：

    randy_container.RemoveFromLogicalTree(randy);
    IDisposable disp = VisualTreeHelper.GetParent(randy) as IDisposable;
    if (disp != null)
        disp.Dispose();

    // Poor Randy is going to heaven...
    StackPanel heaven = new StackPanel();
    heaven.add(randy);

谢谢大家

Answer 1

很有趣，但也很吵。如果你的演示很短，你会更快得到答案。

而不是 removing/adding 视觉你可以简单地 hide/show 它：

void deleteRandy_Click(object sender, RoutedEventArgs e) =>
    randy.Visibility = Visibility.Hidden;

void end_Click(object sender, RoutedEventArgs e) =>
    randy.Visibility = Visibility.Visible;

这样你就不会以不可恢复的方式玩可视化树。如果你真的想删除 UI 元素然后添加 new one.

，你可以使用 MVVM + 数据模板或 x:Shared=False 资源

Answer 2

删除视觉父级似乎没有帮助：

private void end_Click(object sender, RoutedEventArgs e)
{
    IDisposable disp = VisualTreeHelper.GetParent(randy) as IDisposable;
    if (disp != null)
        disp.Dispose();

    DependencyObject parent = VisualTreeHelper.GetParent(randy);
    if (parent == null)
        MessageBox.Show("No parent");

    // If randy is removed properly, this would not crash the application.
    StackPanel s = new StackPanel();
    s.Children.Add(randy);
}

因此您可以创建一个新的 Button:

public MainWindow()
{
    InitializeComponent();
    randy_container.Child = CreateRandyButton();
}

private void end_Click(object sender, RoutedEventArgs e)
{
    StackPanel s = new StackPanel();
    s.Children.Add(CreateRandyButton());
}

private Button CreateRandyButton()
{
    Button button = new Button { Name = "randy", Content = "I am a Randy, the button", ToolTip = "Meet Randy" };
    button.Click += randy_Click;
    return button;
}

...或者按照@Sinatr 的建议简单地隐藏它。

Answer 3

我找到了一个解决方法，以防 parent 仍然是 UIElementIsland。由于它实现了 IDisposable，您可以这样清除它的 children：

var parent = VisualTreeHelper.GetParent(element);
if (parent is IDisposable uiElementIsland)
{
   uiElementIsland.Dispose();
}

这不是很好，但是很管用。

如何从 WPF 中的可视化树分离

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inlineuicontainer