为什么列表框中选定的项目会在表达式混合中引发错误？
我正在使用以下链接学习表达混合 http://visitmix.com/labs/rosetta/EyesOfBlend /数据模板/ 这是关于使用表达式混合的非常好的分步说明。我能够成功完成所有步骤，并且能够运行该程序并得到最终结果。
在步骤(9)之后，在运行项目之前，当我检查设计器时，设计器没有在我在步骤(9)中添加的大图像控件中显示图像。我知道为什么了，由于ListBox的selected索引是-1，所以我将selectedindex更改为0，现在我能够看到图像了。但是，当我编译代码时，出现以下错误
“指定的参数超出了有效值的范围。参数名称：SelectedIndex”
XAML 是
<Grid x:Name="LayoutRoot" Background="White" DataContext="{Binding Source={StaticResource SampleDataSource}}">
<Grid x:Name="itemGrid" DataContext="{Binding SelectedItem, ElementName=listBox}">
<Image Margin="185,56,153,160" Stretch="Fill" Source="{Binding Name}"/>
</Grid>
<ListBox x:Name="listBox" SelectedIndex="0" Margin="8,0,0,8" ItemsSource="{Binding Collection}" ItemTemplate="{StaticResource ItemTemplate1}" ItemsPanel="{StaticResource ItemsPanelTemplate1}" Height="101" VerticalAlignment="Bottom"/>
</Grid>
如果我删除选定的索引，则所有编译都会良好。有人可以解释为什么它在编译后第一次显示，它停止工作吗？
谢谢
I am learning expression blend using the following link http://visitmix.com/labs/rosetta/EyesOfBlend/DataTemplates/
It is a very good step by step instruction on using expression blend. I was able to do all the steps successfully and I was able to run the program and got the final result.
Right after step (9), before running the project, when I checked the designer, the designer did not show the image in the big image control I have added in step (9). I knew why, since the selected index of the ListBox was -1, so I changed the selectedindex to 0, now I was able to see the image. But when I compiled the code I get the following error
"Specified argument was out of the range of valid values. Parameter name:SelectedIndex"
XAML is
<Grid x:Name="LayoutRoot" Background="White" DataContext="{Binding Source={StaticResource SampleDataSource}}">
<Grid x:Name="itemGrid" DataContext="{Binding SelectedItem, ElementName=listBox}">
<Image Margin="185,56,153,160" Stretch="Fill" Source="{Binding Name}"/>
</Grid>
<ListBox x:Name="listBox" SelectedIndex="0" Margin="8,0,0,8" ItemsSource="{Binding Collection}" ItemTemplate="{StaticResource ItemTemplate1}" ItemsPanel="{StaticResource ItemsPanelTemplate1}" Height="101" VerticalAlignment="Bottom"/>
</Grid>
If I remove the selected index, all compile good. Could someone explain why it showed first time after compiling, it stopped working?
Thanks
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绑定到 SelectedItem 几乎总是比绑定到 SelectedIndex 更好。如果 Item 为 null，则绑定应该正常失败。
You are almost always better binding to the SelectedItem than the SelectedIndex. If the Item is null, the binding should fail gracefully.
这可能是因为“Collection”属性在列表框呈现后绑定到项目源。因此，如果没有集合（空），则第一个索引 [0] 不存在，并且会抛出“超出范围异常”。
要解决您的问题，请在填充集合后在代码隐藏中设置选定的索引。希望有帮助。
This is probably because the "Collection" attribute gets bound to the itemsource after the listbox is rendered. So if there is no collection(empty) then the first index [0] does not exist and it throws an "out of range exception".
To resolve your issue set the selected index in code-behind after collection is populated. Hope that helps.