项目集合必须在使用ItemsSource前空 [英] Items collection must be empty before using ItemsSource

问题描述

如果我把一个DataTrigger在一个简单的列表框我得到这个运行时异常：

产品集合必须在使用ItemsSource之前<空/ p>

我的列表框中没有datatrigger（也不例外）：

 < ListBox中的ItemsSource ={结合EdgedBoards}的SelectedItem ={结合SelEdgedBoard，模式=双向}的DisplayMemberPath =名称> 
< ListBox.ItemContainerStyle> 
<风格的TargetType ={X：输入一个ListBoxItem}
支持算法FMP ={StaticResource的{X：输入一个ListBoxItem}}> 
 
< setter属性=IsSelected
值={结合IsSelected，模式=双向，UpdateSourceTrigger =的PropertyChanged}/> 
< /样式和GT; 
< /ListBox.ItemContainerStyle> 
< /列表框>   

我的列表框与 DataTrigger >

 < ListBox中的ItemsSource ={结合EdgedBoards}的SelectedItem ={结合SelEdgedBoard，模式=双向}的DisplayMemberPath =名称> ; 
<风格的TargetType ={X：类型列表框}支持算法FMP ={StaticResource的{X：类型列表框}}> 
< setter属性=调焦VALUE =真/> 
 
< Style.Triggers> 
< DataTrigger绑定={绑定的ElementName = EdgedBoardsAdd_UC，路径=能见度}VALUE =可见> 
< setter属性=调焦VALUE =FALSE/> 
< / DataTrigger> 
< /Style.Triggers> 
< /样式和GT; 
 
< ListBox.ItemContainerStyle> 
<风格的TargetType ={X：输入一个ListBoxItem}支持算法FMP ={StaticResource的{X：输入一个ListBoxItem}}> 
< setter属性=IsSelectedVALUE ={结合IsSelected，模式=双向，UpdateSourceTrigger =的PropertyChanged}/> 
< /样式和GT; 
< /ListBox.ItemContainerStyle> 
< /列表框> 
  

这有什么错后者的代码？

解决方案

您未正确申报的风格，所以它被设置为的内容的ListBox的 - 你是手工声明包含一个样式列表

您应该与<包装现有的风格元素; ListBox.Style> 元素来解决这个问题。

If I put a DataTrigger in a simple Listbox I get this runtime exception:

Items collection must be empty before using ItemsSource

My listbox without datatrigger (no exception):

<ListBox ItemsSource="{Binding EdgedBoards}" SelectedItem="{Binding SelEdgedBoard, Mode=TwoWay}" DisplayMemberPath="Name">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}" 
               BasedOn="{StaticResource {x:Type ListBoxItem}}">

            <Setter Property="IsSelected"
                    Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

My ListBox with DataTrigger:

<ListBox ItemsSource="{Binding EdgedBoards}" SelectedItem="{Binding SelEdgedBoard, Mode=TwoWay}" DisplayMemberPath="Name">
    <Style TargetType="{x:Type ListBox}" BasedOn="{StaticResource {x:Type ListBox}}">
        <Setter Property="Focusable" Value="True" />

        <Style.Triggers>
            <DataTrigger Binding="{Binding ElementName=EdgedBoardsAdd_UC, Path=Visibility}" Value="Visible">
                <Setter Property="Focusable" Value="False" />
            </DataTrigger>
        </Style.Triggers>
    </Style>

    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}" BasedOn="{StaticResource {x:Type ListBoxItem}}">
            <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

What's wrong with the latter code?

解决方案

You aren't declaring the style correctly, and so it's being set as the content of the listbox - you are manually declaring a list that contains a single style.

You should wrap your existing Style element with the <ListBox.Style> element to fix this problem.

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