显示Silverlight的组合框标题 [英] Show ComboBox group header for Silverlight
问题描述
我想在Silverlight中显示 ComboBox 与 OPTGROUP 样式标题。
例如：
我发现的每个网站（包括SO的问题）都会将此链接拖放到过时的链接， / p>>
那么我该如何做呢？
它不坏，应该足够灵活 - 虽然它有弱点，需要一个扩展的集合类（不能使用CollectionViewSource）。
步骤1 ComboBoxGroupHeader对象
这起到了@NiteshChordiya提到的虚拟条目的作用。
public class ComboBoxGroupHeader
{
public ComboBoxGroupHeader（object header）
{
Header = header;
}
public object Header {get;保护集; }
}
第2步 / em>
这将覆盖 PrepareContainerForItemOverride ，以便修改虚拟项目的容器。它还提供（可选）HeaderTemplate。
public class GroupedComboBox：ComboBox
{
public DataTemplate HeaderTemplate
{
get {return（DataTemplate）GetValue（HeaderTemplateProperty）; }
set {SetValue（HeaderTemplateProperty，value）; }
}
public static readonly DependencyProperty HeaderTemplateProperty =
DependencyProperty.Register（HeaderTemplate，typeof（DataTemplate），typeof（GroupedComboBox），new PropertyMetadata（null））;
protected override void PrepareContainerForItemOverride（DependencyObject元素，对象项）
{
base.PrepareContainerForItemOverride（element，item）;
var container = element as ComboBoxItem;
if（container！= null&& item is ComboBoxGroupHeader）
{
//防止选择
container.IsHitTestVisible = false;
//调整容器以显示标题内容
container.ContentTemplate = HeaderTemplate
container.Content =（（ComboBoxGroupHeader）item）.Header;
}
}
}
/ strong> 扩展集合类
这样做了分组，并添加了ComboBoxGroupHeader虚拟条目。这个实现基本上是只读的（如果你试图添加新项目，分组将会中断），但它将直接支持像Add，Insert等操作。
public class GroupedCollection< T，TGroup> ：ObservableCollection< object>
{
private Func< T，TGroup> _grouping;
public IEnumerable< T> BaseItems
{
get {return base.Items.OfType< T>（）; }
}
public GroupedCollection（IEnumerable< T> initial，Func< T，TGroup> grouping）
：base（GetGroupedItems（initial，
_grouping = grouping;
}
private static IEnumerable< object> GetGroupedItems（IEnumerable< T> items，Func< T，TGroup> grouping）
{
return item
.GroupBy（grouping）
.SelectMany（grp =>
new object [] {new ComboBoxGroupHeader（grp.Key）}
.Union（grp.OfType< object>（））
）;
}
}
使用 >
它像一个普通的 ComboBox ，可选的 HeaderTemplate
< local：GroupedComboBox ItemsSource ={Binding Source}>
< local：GroupedComboBox.HeaderTemplate>
< TextBlock FontSize =9TextDecorations =UnderlineForeground =DarkGray
Text ={Binding}/>
< / local：GroupedComboBox.HeaderTemplate>
< / local：GroupedComboBox>
要使分组生效，源必须使用上述GroupedCollection伪标题项。示例：
public class Item
{
public string Name {get;组; }
public string Category {get;组; }
public Item（string name，string category）
{
Name = name;
Category = category;
}
}
public class Item：GroupedCollection< Item，string>
{
public Items（IEnumerable< Item> items）
：base（items，item => item.Category）{}
}
public class ViewModel
{
public IEnumerable< Item>源{get;私人集}
public ViewModel（）
{
Source = new Items（new Item [] {
new Item（Apples，Fruits），
new Item（Carrots，Vegetables），
new Item（Bananas，Fruits），
new Item（Lettuce，Vegetables），
新项目（Oranges，Fruits）
}）;
}
}
I want to show a ComboBox with OPTGROUP style header gruopings in Silverlight. Every website I find (including questions on SO) that sovle this link to an outdated link and, handily, show no code snippets for me to work from.
E.g.:
So how do I do this?
Here is one generalized approach. It's not bad, and should be flexible enough -- although it has the weakness of requiring an extended collection class (cannot make use of CollectionViewSource).
Step 1 ComboBoxGroupHeader object
This plays the role of "dummy entry" mentioned by @NiteshChordiya.
public class ComboBoxGroupHeader
{
public ComboBoxGroupHeader(object header)
{
Header = header;
}
public object Header { get; protected set; }
}
Step 2 Extended ComboBox
This overrides PrepareContainerForItemOverride, in order to tinker with the dummy items' containers. It also provides an (optional) "HeaderTemplate".
public class GroupedComboBox : ComboBox
{
public DataTemplate HeaderTemplate
{
get { return (DataTemplate)GetValue(HeaderTemplateProperty); }
set { SetValue(HeaderTemplateProperty, value); }
}
public static readonly DependencyProperty HeaderTemplateProperty =
DependencyProperty.Register("HeaderTemplate", typeof(DataTemplate), typeof(GroupedComboBox), new PropertyMetadata(null));
protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
{
base.PrepareContainerForItemOverride(element, item);
var container = element as ComboBoxItem;
if (container != null && item is ComboBoxGroupHeader)
{
// prevent selection
container.IsHitTestVisible = false;
// adjust the container to display the header content
container.ContentTemplate = HeaderTemplate
container.Content = ((ComboBoxGroupHeader)item).Header;
}
}
}
Step 3 Extended collection class
This does the grouping, and adds the dummy "ComboBoxGroupHeader" entries. This implementation is essentially read-only (groupings would break if you tried to add new items), but it would be straight-forward to support operations like "Add", "Insert", etc.
public class GroupedCollection<T, TGroup> : ObservableCollection<object>
{
private Func<T, TGroup> _grouping;
public IEnumerable<T> BaseItems
{
get { return base.Items.OfType<T>(); }
}
public GroupedCollection(IEnumerable<T> initial, Func<T, TGroup> grouping)
: base(GetGroupedItems(initial, grouping))
{
_grouping = grouping;
}
private static IEnumerable<object> GetGroupedItems(IEnumerable<T> items, Func<T, TGroup> grouping)
{
return items
.GroupBy(grouping)
.SelectMany(grp =>
new object[] { new ComboBoxGroupHeader(grp.Key) }
.Union(grp.OfType<object>())
);
}
}
Usage
It works like a normal ComboBox, with the optional HeaderTemplate:
<local:GroupedComboBox ItemsSource="{Binding Source}">
<local:GroupedComboBox.HeaderTemplate>
<TextBlock FontSize="9" TextDecorations="Underline" Foreground="DarkGray"
Text="{Binding}" />
</local:GroupedComboBox.HeaderTemplate>
</local:GroupedComboBox>
For the grouped to take effect, the source must use the "GroupedCollection" above, so as to include the dummy header items. Example:
public class Item
{
public string Name { get; set; }
public string Category { get; set; }
public Item(string name, string category)
{
Name = name;
Category = category;
}
}
public class Items : GroupedCollection<Item, string>
{
public Items(IEnumerable<Item> items)
: base(items, item => item.Category) { }
}
public class ViewModel
{
public IEnumerable<Item> Source { get; private set; }
public ViewModel()
{
Source = new Items(new Item[] {
new Item("Apples", "Fruits"),
new Item("Carrots", "Vegetables"),
new Item("Bananas", "Fruits"),
new Item("Lettuce", "Vegetables"),
new Item("Oranges", "Fruits")
});
}
}
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