指定的元素已经是另一个元素的逻辑子元素.先断开连接" [英] Specified element is already the logical child of another element. Disconnect it first”

问题描述

我有包含网格的用户控件，其中有扩展器问题是当我尝试打开使用此用户控件的新窗口时出现异常指定元素已经是另一个元素的逻辑子元素.首先断开它
这是我的代码及其在创建第一个窗口时的工作显示第二个窗口时出现异常

i have user control that contain grid and inside it there is expander the problem is when i try to open new window that uses this user control i get an exception " Specified element is already the logical child of another element. Disconnect it first"
here is my code and its work when first windows created and the exception occur when show the second window

 <UserControl x:Class="DiagramDesigner.WindowsUserControl"
                     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                     xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
                     xmlns:s="clr-namespace:DiagramDesigner"
                xmlns:c="clr-namespace:DiagramDesigner.Controls"
                     mc:Ignorable="d" 

                     d:DesignHeight="700" d:DesignWidth="1000">
            <UserControl.Resources>
                <ContextMenu x:Key="DesignerCanvasContextMenu">
                    <MenuItem Header="Paste" Command="{x:Static ApplicationCommands.Paste}">
                        <MenuItem.Icon>
                            <Image Source="Resources/Images/Paste.png" Width="16"/>
                        </MenuItem.Icon>
                    </MenuItem>
                    <MenuItem Header="Select All" Command="{x:Static s:DesignerCanvas.SelectAll}"/>
                </ContextMenu>
            </UserControl.Resources>

            <Grid Margin="10">
                <Grid.RowDefinitions>

                    <RowDefinition Height="*"/>
                </Grid.RowDefinitions>


                <Grid Grid.Row="1" Margin="0,10,0,0">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="200"/>
                        <ColumnDefinition/>
                    </Grid.ColumnDefinitions>
                    <!-- Toolbox -->
                    <StackPanel Grid.Column="0" Margin="0,0,5,0">
                        <Expander Header="Flow Chart" Content="{StaticResource FlowChartStencils}" IsExpanded="True" />
                    </StackPanel>
                    <!-- GridSplitter -->
                    <GridSplitter Focusable="False" Width="2" Background="LightGray"
                            VerticalAlignment="Stretch" HorizontalAlignment="Right"/>
                    <!-- Designer -->
                    <GroupBox Header="Diagram" Grid.Column="1" Margin="3,0,0,0">
                        <ScrollViewer HorizontalScrollBarVisibility="Auto"
                              VerticalScrollBarVisibility="Auto">
                            <s:DesignerCanvas Focusable="true" x:Name="MyDesigner"
                                    Background="{StaticResource WindowBackgroundBrush}"
                                    Margin="10" FocusVisualStyle="{x:Null}"
                                    ContextMenu="{StaticResource DesignerCanvasContextMenu}"/>
                        </ScrollViewer>
                    </GroupBox>
                </Grid>
            </Grid>
       </UserControl>

推荐答案

您不能为 UI 的不同部分重复使用相同的 UIElement 实例.要么从第一个中删除它并将其添加到第二个中(不推荐，但有一些高级场景是有意义的)或简单地创建一个新的.挺便宜的.

You cannot reuse the same UIElement instance for different parts of the UI. Either remove it from the first and add it to the second one (not recommended but there are some advanced scenarios were it makes sense) or simply create a new one. It's pretty cheap.

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