无法在WPF TextBlock中获得垂直滚动条(Unable to get vertical scroll bars in an WPF TextBlock)

 我在wpf TextBlock控件（.Net 3.5）中呈现文本。 文本块的内容取决于用户在列表框中选择的内容。 文字包装，所以我不需要水平滚动条。 但是，通常有更多的文本不能显示窗口的数量，所以我需要一个垂直滚动条。 
 
 在我开始搜索时，我很快发现答案是将TextBlock包装在ScrollViewer中。 但是，它不工作（TM），我希望有人可以帮我找出原因。 
 
 这是UI代码的结构： 
 
<Window x:Class=..>
    <StackPanel>
        <ListBox HorizontalAlignment="Stretch"
                 VerticalAlignment="Top"  Height="200"
                 SelectionChanged="listbox_changed" SelectionMode="Single">
        </ListBox>
        <Button Click="Select_clicked">Select</Button>
        <ScrollViewer VerticalScrollBarVisibility="Auto">
            <TextBlock Name="textblock" TextWrapping="Wrap"/>
        </ScrollViewer>
    </StackPanel>
</Window>
 
 当用户在列表框中选择一个项目时，与该项目相关的一些文本将显示在TextBlock中。 我原以为代码应该是所有必需的，但它从来没有给我提供一个滚动条。 
 
 搜索和实验给了我两个线索：问题的根源可能与我动态更新TextBlock的内容有关，并且TextBlock不会根据新内容调整自身的大小。 我发现一个似乎相关的帖子，说通过将TextBlock的高度设置为其ActualHeight（在更改其内容之后），它将起作用。 但它没有（我看不到这个效果）。 
 
 其次，如果我设置ScrollViewer的高度（在设计时间内），那么我会得到一个垂直滚动条。 例如，如果我在上面的xaml中将它设置为300，那么结果几乎是好的，因为当我需要它时，第一次打开的窗口包含一个带有垂直滚动条的TextBlock。 但是，如果我使窗口更大（在运行时用鼠标调整大小），ScrollViewer不会利用新的窗口大小，而是根据xaml保持其高度，当然这不会。 
 
 希望我只是忽略了一些显而易见的事情。 
 
 谢谢！ 

I'm presenting text in a wpf TextBlock control (.Net 3.5). The content of the textblock varies depending on what the user selects in a list box. The text wraps, so I don't need an horizontal scroll bar. However, there is often more text than the amount the window can display, so I need a vertical scroll bar.
 
As I started searching I quickly found that the answer is to wrap the TextBlock in a ScrollViewer. However, It Does Not Work (TM) and I'm hoping someone can help me work out why.
 
This is the structure of the UI code:
 
<Window x:Class=..>
    <StackPanel>
        <ListBox HorizontalAlignment="Stretch"
                 VerticalAlignment="Top"  Height="200"
                 SelectionChanged="listbox_changed" SelectionMode="Single">
        </ListBox>
        <Button Click="Select_clicked">Select</Button>
        <ScrollViewer VerticalScrollBarVisibility="Auto">
            <TextBlock Name="textblock" TextWrapping="Wrap"/>
        </ScrollViewer>
    </StackPanel>
</Window>
 
When the user selects an item in the list box, some text associated with this item is presented in the TextBlock. I would have thought that the code as it stands should have been all that's required, but it never provides me with a scroll bar.
 
Searching and experimenting have given me two clues: the root of the problem might be related to me updating the content of the TextBlock dynamically, and that the TextBlock does not resize itself based on the new content. I found a posting that seemed relevant that said that by setting the Height of the TextBlock to its ActualHeight (after having changed its content), it would work. But it didn't (I can see no effect of this).
 
Second, if I set the height (during design time) of the ScrollViewer, then I do get a vertical scroll bar. For instance, if I set it to 300 in the xaml above, the result is almost good in that the window as first opened contains a TextBlock with a vertical scroll bar when (and only when) I need it. But if I make the window larger (resizing it with the mouse during runtime), the ScrollViewer does not exploit the new window size and instead keeps its height as per the xaml which of course won't do.
 
Hopefully, I've just overlooked something obvious..
 
Thanks!

原文：https://stackoverflow.com/questions/5621086