Silverlight 组合框显示的项目数刷新 [英] Silverlight combobox number of items shown refresh
问题描述
我在 SL 页面上有两个组合框.当 Combo 1 更新时，会调用一个服务并填充 Combo 2.
I have two combo boxes on a SL page. When Combo 1 updates, a service is called and populates Combo 2.
在第一次调用时，返回 3 个结果.当组合框展开时，您可以看到所有 3 个选项.
On the first call, 3 results are returned. When the combo box is expanded, you can see all 3 options.
在第二次调用时，返回 4 个结果.当组合框展开时，您可以看到 3 个选项，带有垂直滚动条.
On the second call, 4 results are returned. When the combo box is expanded, you can see 3 options, with a vertical scroll bar.
如果我重新加载并反向执行这些步骤，我会在第一次调用时得到 4 行，在第二次调用时得到 3 行 + 一个空白行.(不，空白不是记录.它不能被选中.)
If I reload and do those steps in reverse, I get 4 rows the first call and 3 rows + a blank row on the second call. (No, the blank is not a record. It cannot be selected.)
下拉列表的大小似乎保持了第一个生成的高度.
It appears that the drop down list size keeps the first generated height.
如何刷新每次服务调用后显示的组合框最大项目数?
How can I refresh the combo box max items shown after each service call?
谢谢！
编辑 #1
代码遵循 M-V-VM 模式.当页面加载时，Group1 填充第一个组合框，并且没有选择任何内容.当用户进行选择时，该选择将绑定到 Group1Selection.
The code follows the M-V-VM pattern. When the page loads, the Group1 populates the first combo box, and nothing is selected. When the user makes a selection, that selection is bound to Group1Selection.
<ComboBox ItemsSource="{Binding Path=Group1}" SelectedItem="{Binding Path=Group1Selection}" />
<ComboBox ItemsSource="{Binding Path=Group2}" SelectedItem="{Binding Path=Group2Selection}" />
在视图模型中，在 Group1Selection 属性的 set 访问器中，我有类似的东西
In the viewmodel, in the set accessor of the Group1Selection property, I have something like
set
{
if (group1Selection != value)
{
group1Selection = value;
PopulateGroup2();
OnPropertyChanged("Group1Selection");
}
}
PopulateGroup2 在何处执行我的服务调用异步、获取数据并将该数据放入 Group2 的公开属性中.
Where PopulateGroup2 performs my service call async, gets the data, and puts that data into the exposed property of Group2.
在正常"条件下，这不是问题，因为大多数选项都有数十种可能的选择.但是，几个 Group1 选项只有 3 或 4 个子选项.如果首先选择其中一个，则该应用程序实例其余部分的 ComboBox 高度分别设置为 3 或 4，而不是最大显示 8 个项目.
Under "normal" conditions, this isn't a problem, since most options have dozens of possible selections. However, a couple of the Group1 choices only have 3 or 4 child choices. If one of those is selected first, then the height of the ComboBox, for the rest of that application instance is set to 3 or 4, respectively, instead of maxing out at 8 shown items.
遵循 M-V-VM 模式，代码隐藏中没有代码.
Following the M-V-VM pattern, there is no code in the code-behind.
推荐答案
这是 Silverlight 2 中 ComboBox 中的一个已知错误.我认为它已在 SL 3 中修复.
This is a known bug in the ComboBox in Silverlight 2. I think its been fixed in SL 3.
您可以通过执行以下操作来解决此问题:
You can fix this by doing the following:
从组合框继承
Inherit from the ComboBox
公共类 MyComboBox : ComboBox
public class MyComboBox : ComboBox
在 OnApplyTemplate() 方法中获取对 ComboBox 的弹出"部分的引用
Get a reference to the "Popup" part of the ComboBox inside the OnApplyTemplate() method
Popup thePopup = GetTemplateChild("Popup") as Popup;
FrameworkElement thePopupContent = thePopup.Child as FrameworkElement;
覆盖 OnItemsChanged 方法
Override the OnItemsChanged method
在重写的 OnItemsChagned 方法内部重置 Height &使用 ClearValue(DP) 方法的 Popup 上的宽度依赖属性.
Inside the overridden OnItemsChagned method reset the Height & Width dependency properties on the Popup using the ClearValue(DP) method.
thePopupContent.ClearValue(FrameworkElement.WidthProperty);
thePopupContent.ClearValue(FrameworkElement.HeightProperty);
您可以清除最大和最小高度 &如果您也担心宽度属性.
You can clear the Max and Min Height & Width properties if you are worried about those too.
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