没有参数​​传递给定制DataTemplateSelector的SelectTemplate（）。为什么？ [英] No Parameters are passed to SelectTemplate() of custom DataTemplateSelector. Why?

问题描述

我使用了一个 CellTemplateSelector 来有条件地显示在DataGrid列中的选中标记。

I'm using a CellTemplateSelector to conditionally display a checkmark in a DataGrid Column.

方法 SelectTemplate（对象项目，DependencyObject的容器）我的 DataTemplateSelector 类被称为但是参数产品空而不是预期的 DataRowView的 -object。

The method SelectTemplate(object item, DependencyObject container) of my DataTemplateSelector class is called but the parameter item is null instead of the expected DataRowView-object.

下面是XAML- code。在地产的ItemsSource DataGrid中的项目是数据表，这对于其他列正常工作。 （我与Visual Studio防爆preSS工作2010 的）

Here is the XAML-Code. Items in Property ItemsSource of DataGrid is a DataTable, which works fine for the other columns. (I work with Visual Studio Express 2010)

...
<Window.Resources>        
        <DataTemplate x:Key="CheckedTemplate">
            <Path Width="16" Height="16" Margin="6,0,0,0" 
            x:Name="CheckMark" SnapsToDevicePixels="False"
            Stroke="Green" Fill="Green" StrokeThickness="1"
            Data="M 12.4227,0.00012207C 12.4867,0.126587 12.5333,0.274536 
            12.6787,0.321411C 9.49199,3.24792 6.704,6.57336 
            4.69865,10.6827C 4.04399,11.08 3.47066,11.5573 2.83199,
            11.9706C 2.09467,10.2198 1.692,8.13196 3.8147e-006,
            7.33606C 0.500004,6.79871 1.31733,6.05994 1.93067,6.2428C 
            2.85999,6.51868 3.14,7.9054 3.60399,8.81604C 5.80133,
            5.5387 8.53734,2.19202 12.4227,0.00012207 Z " />
        </DataTemplate>
        <DataTemplate x:Key="UncheckedTemplate">
        </DataTemplate>

        <local:CheckmarkTemplateSelector x:Key="CheckmarkTemplateSelector"  CheckedTemplate="{StaticResource CheckedTemplate}" UncheckedTemplate="{StaticResource UncheckedTemplate}" />
    </Window.Resources>
...
<DataGrid ItemsSource="{Binding Items, Mode=OneWay}"  AutoGenerateColumns="False">            
    <DataGrid.Columns>
        <DataGridTextColumn Header="No" Binding="{Binding no}" IsReadOnly="True" />
        <DataGridTextColumn Header="Name" Binding="{Binding name}" IsReadOnly="True" />
        <DataGridTemplateColumn Header="Selected" CellTemplateSelector="{StaticResource CheckmarkTemplateSelector}" />
    </DataGrid.Columns>
</DataGrid>
...

任何帮助是AP preciated。先谢谢了。

Any help is appreciated. Thanks in advance.

推荐答案

你确定它一直通过为空，或者仅仅是第一次？该 CellTemplateSelector 与空项目设置逻辑树时，则调用一次每个数据项与<调用一次code>项目通过绑定的对象。你可能只是没有在第一个空。

Are you sure it's always passed null, or just the first time? The CellTemplateSelector is called once with a null item when setting up the logical tree, then called once per data item with item passed the bound object. You may just be failing on the first null.

也看到这一问题：<一href="http://stackoverflow.com/questions/2534339/why-is-the-selecttemplate-method-run-2-times-in-debug-mode">Why是SelectTemplate方法运行2次在调试模式？

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