强制 ComboBox 在 Silverlight 中打开？
我在 Silverlight 中有一个 ComboBox，其行为非常不一致。
我将组合框绑定到动态数据集合，在其中添加或删除元素。下面是 ComboBox 的 XAML：
<ComboBox Margin="0,-1,0,0" Width="20" Grid.Row="0" Grid.Column="0" ItemsSource="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=ItemsContained}" x:Name="TabComboBox" >
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Background="White" MinWidth="250" />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
因此，这非常有效，ComboBox 将“向上”打开，其中包含 ItemsContained 中的一长串项目。但是，如果我删除 ItemsContained 中的一项，则当您单击 ComboBox 时，它会突然从打开“向上”切换为打开“向下”，尽管事实上该集合中有很多项，并且存在只有 20 像素左右的空间可以向下打开。我无法弄清楚这一点。我什至尝试将 ItemsPanelTemplate 设置为 MinHeight，但这没有帮助。有谁知道如何使组合框始终“向上”打开？
另外，即使我将 MinHeight 设置为一些荒谬的值，例如 10,000，它仍然会这样做。
编辑：作为更新，我通过每次 ItemsContained 更改时创建一个全新的 ComboBox 来实现此目的。这是代码：
scrollingGrid.Children.Remove(tabComboBox);
tabComboBox.ItemsSource = null;
ComboBox boxy = new ComboBox()
{
ItemsSource = ItemsContained
};
scrollingGrid.Children.Add(boxy);
tabComboBox = boxy;
我觉得这有点临时，所以如果有人有更好的想法，请告诉我。更改 ComboBox 内 ScrollViewer 的高度也不起作用。
I have a ComboBox in Silverlight that has very inconsistent behavior.
I have the ComboBox bound to a dynamic collection of data where elements are added or removed. Here is the XAML for the ComboBox:
<ComboBox Margin="0,-1,0,0" Width="20" Grid.Row="0" Grid.Column="0" ItemsSource="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=ItemsContained}" x:Name="TabComboBox" >
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Background="White" MinWidth="250" />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
So this works great and the ComboBox opens "up" with the long list of items in ItemsContained. However, if I delete one of the items in ItemsContained, the ComboBox all of a sudden will switch from opening "up" to opening "down" when you click on it, despite the fact there are a lot of items in this collection and there is only 20 or so pixels of room for it to open down. I cannot figure this out. I have even tried setting the ItemsPanelTemplate to have a MinHeight, but that does not help. Does anyone know how to make the ComboBox always open "up"?
Also, even if I set the MinHeight to something ridiculous, such as 10,000, it still does this.
EDIT: As an update, I have gotten this to work by creating a whole new ComboBox every time ItemsContained is changed. This is the code:
scrollingGrid.Children.Remove(tabComboBox);
tabComboBox.ItemsSource = null;
ComboBox boxy = new ComboBox()
{
ItemsSource = ItemsContained
};
scrollingGrid.Children.Add(boxy);
tabComboBox = boxy;
I feel this is a little ad hoc, so if anyone has a better idea, let me know. Changing the height of the ScrollViewer inside the ComboBox does not work either.
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我认为这是一个 Silverlight Bug。当您设置 ItemsSource 属性时，组合框弹出窗口的行为会从向上更改为向下。
我在每个组合框的 DropDownClosed 事件中克隆了我的组合框，这对我有用。
I think this is a Silverlight Bug. When you set the ItemsSource property the behavior of the combobox popup changes from up to down.
I Clone my combobox in the event DropDownClosed of each combobox and that works for me.
我不确定这个解决方案会比您当前的修复方案更加临时，但我想我会提供它。
我编辑了 ComboBox 模板的副本，原始的 ItemsPresenter 中只有一个 ScrollViewer，我添加了一个边距为 0,5000,0,0 的矩形，以便内部 Popup 代码始终将其放置在顶部。我还将模板绑定移至 ScrollViewer，这样即使没有足够的项目，它也不会拉伸到顶部。
样式有点长，但就在这里，只需将其放入资源 xaml 中即可（并将 ComboBox 的样式设置为 ComboBoxStyle1）。让我知道它对您有何作用！
I'm not sure this solution will be any less ad hoc than your current fix, but I figured I'd offer it.
I edited a copy of the ComboBox template, and where the original only had a ScrollViewer in an ItemsPresenter, I added a Rectangle with Margin 0,5000,0,0, so that the internal Popup code would place it on the top always. I also moved the template bindings to the ScrollViewer so that it wouldn't stretch to the top even if there weren't enough items.
The style is a little long but here it is, just throw it in your resources xaml (and set the style of your ComboBox to ComboBoxStyle1). Let me know how it works for you!