一个ListView的ItemsPanelTemplate apperently抛出worngly异常 [英] ItemsPanelTemplate of a ListView throws apperently worngly an exception

问题描述

我创建了包含自定义ItemsPanelTemplate一个ListView的用户控件。

I created a user control which contains a ListView with a custom ItemsPanelTemplate.

<UserControl x:Class="..."
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Name="thisUserControl">
<ListView ItemsSource="{Binding Source={StaticResource cvs}}"
          Name="mainListView">
    <ListView.GroupStyle>
        <GroupStyle>
            ...
        </GroupStyle>
    </ListView.GroupStyle>
    <ListView.ItemsPanel>
        <ItemsPanelTemplate>
            <cd:TimeLinePanel UnitsPerSecond="{Binding ElementName=thisUserControl,Path=DataContext.UnitsPerSecond}" Start="{Binding ElementName=thisUserControl, Path=DataContext.Start}"/>
        </ItemsPanelTemplate>
    </ListView.ItemsPanel>
</ListView>

在用户控件的DataContext的有两个属性开始和UnitsPerSecond。当我使用我组不能简单地写

The DataContext of the UserControl has two properties Start and UnitsPerSecond. As I am using groups I cannot simply write

Start={Binding Path=.Start}

于是我用上面的code。但是，如果我更改启动的结合这一点，我得到一个异常：

Thus I used the code above. But if I change the binding of Start to this I get an exception:

的 ItemsPanelTemplate的的VisualTree必须是单个元素。的

显然ItemsPanelTemplate得到了只是一个单一的元件。

Obviously the ItemsPanelTemplate has got just a single element.

所以，可能是什么问题呢？我的自定义面板不会产生任何元素。它只是安排他们。

So what could be the problem? My custom panel does not create any elements. It just arranges them.

先谢谢了。

推荐答案

您很可能收到此异常，因为你想孩子添加到TimeLinePanel（或要覆盖面板的可视化树，并返回比其他东西1VisualChildrenCount）。可悲的是，如果是因为ItemsPanelTemplate的一个ItemsControl内部创建你不能修改面板的孩子属性。一个ItemsControl以外，不存在问题。

You are receiving this exception probably because you are trying to add "Children" to TimeLinePanel (or you are overriding the visual tree of the panel and returning something other than 1 in "VisualChildrenCount"). Sadly, you cannot modify the "Children" property of a panel if it is created inside an ItemsControl because of an ItemsPanelTemplate. Outside of an ItemsControl, there is no problem.

另外，你可以覆盖的ListView的模板类似下面的 - 它的作品在我的情况，并摆脱了异常

Alternatively, you can override the template of ListView to something like the following - it works in my case, and gets rid of the exception.

<ListView.Template>
    <ControlTemplate>
        <cd:TimeLinePanel IsItemsHost="True" UnitsPerSecond="..."/>
    <ControlTemplate>
</ListView.ItemsPanel>

有一个$ C $的CProject文章（ HTTP：// WWW。 codeproject.com / KB / WPF / ConceptualChildren.aspx ），这也是对这种行为的一些细节，这可能会帮助你理解为什么它是这样的。

There is a CodeProject article (http://www.codeproject.com/KB/WPF/ConceptualChildren.aspx) which gives some details on this behavior, which may help you understand why it is the case.

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