当谈到我在WPF中当前的绑定需求时，我处于绑定（没有双关语）。我花了大部分时间试图研究我的问题，我找不到解决问题的可靠方法。这是：
我正在尝试创建一个用户控件来表示我所称的工作空间（Josh Smith的博客引用）。工作区将显示在选项卡控件中。我的目标是使用选项卡式界面来管理我打开的各种文档，就像在一本激动人心的工作簿的浏览器中一样。
每次用户使用新工作区时，该工作区都应显示在选项卡控件中。每个工作空间采用用户控件的形式，每个工作空间都有自己的视图模型。我希望Tab Header能够从我的视图模型中显示一个属性，我认为它可能必须通过我的用户控件作为属性公开。
到目前为止，在我遇到很多问题之前，我最喜欢的最干净的解决方案是使用datatemplates。基本上我做了以下几点：
<DataTemplate x:Key="WorkspaceItem">
<DockPanel Width="120">
<ContentPresenter
Content="{Binding Title}"
VerticalAlignment="Center"
/>
</DockPanel>
</DataTemplate>
<DataTemplate DataType="{x:Type CustomerViewModel}">
<workspace:CustomerWorkspace />
</DataTemplate>
<TabControl ItemsSource="{Binding Workspaces}" ItemTemplate="{StaticResource WorkspaceItem}"/>
TabControl.ItemsSource绑定到包含所有工作空间的observablecollection（Object）。
除了两件事之外，这很有效：
如果我打开多个客户，那么我打开了多个工作区。由于DataTemplate Recycling，当我从一个选项卡切换到另一个选项卡时，我会丢失状态。所以没有约束的一切都会失去状态。
不同工作区（使用不同的数据窗口）之间交换的性能非常慢。
所以......我在SO上找到了另一个用户的建议，将用户控件添加到ObservableCOllection并抛弃了数据模板。现在解决了失去国家的问题之一。但是，现在我面临着剩下的两个问题：
然后我继续在我的代码隐藏中向ObservableCollection添加一个TabItem，并将TabItem.Content属性设置为用户控件的属性。由于我已经删除了DataTemplates的使用，速度问题现在已经消除，因为失败状态问题。但是，我现在仍然遇到将TabItem.header绑定到我的usercontrol的Custome“Title”属性的问题，该属性应该显示在选项卡标题中。
所以在这篇非常长的帖子之后，我的问题是：
有没有办法使用datatemplates并强制它们为集合中的每个项目创建一个新实例，以防止回收和状态丢失。
1a上。有没有比我在上面的帖子中提到的更好的替代方案？
有没有办法通过Xaml而不是通过Tab项的后端代码构造来完成所有这些？
答案 0 :(得分：5)
WPF的默认行为是卸载不可见的项目，其中包括卸载不可见的TabItems。这意味着当您返回选项卡时，TabItem会重新加载，任何未绑定的内容（例如滚动位置，控件状态等）都将被重置。
有一个很好的网站here，其中包含扩展TabControl的代码，并阻止它在切换标签时销毁TabItems，但现在似乎不再存在。
这是代码的副本，虽然我已对其进行了一些更改。切换选项卡时，它会保留ContentPresenter TabItems，并在您返回页面时使用它重绘TabItem。它占用了更多的内存，但是我发现它在性能上更好，因为TabItem不再需要重新创建它上面的所有控件。
// Extended TabControl which saves the displayed item so you don't get the performance hit of
// unloading and reloading the VisualTree when switching tabs
// Obtained from http://eric.burke.name/dotnetmania/2009/04/26/22.09.28
// and made a some modifications so it reuses a TabItem's ContentPresenter when doing drag/drop operations
[TemplatePart(Name = "PART_ItemsHolder", Type = typeof(Panel))]
public class TabControlEx : System.Windows.Controls.TabControl
{
// Holds all items, but only marks the current tab's item as visible
private Panel _itemsHolder = null;
// Temporaily holds deleted item in case this was a drag/drop operation
private object _deletedObject = null;
public TabControlEx()
: base()
{
// this is necessary so that we get the initial databound selected item
this.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;
}
/// <summary>
/// if containers are done, generate the selected item
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
if (this.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
{
this.ItemContainerGenerator.StatusChanged -= ItemContainerGenerator_StatusChanged;
UpdateSelectedItem();
}
}
/// <summary>
/// get the ItemsHolder and generate any children
/// </summary>
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
_itemsHolder = GetTemplateChild("PART_ItemsHolder") as Panel;
UpdateSelectedItem();
}
/// <summary>
/// when the items change we remove any generated panel children and add any new ones as necessary
/// </summary>
/// <param name="e"></param>
protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)
{
base.OnItemsChanged(e);
if (_itemsHolder == null)
{
return;
}
switch (e.Action)
{
case NotifyCollectionChangedAction.Reset:
_itemsHolder.Children.Clear();
if (base.Items.Count > 0)
{
base.SelectedItem = base.Items[0];
UpdateSelectedItem();
}
break;
case NotifyCollectionChangedAction.Add:
case NotifyCollectionChangedAction.Remove:
// Search for recently deleted items caused by a Drag/Drop operation
if (e.NewItems != null && _deletedObject != null)
{
foreach (var item in e.NewItems)
{
if (_deletedObject == item)
{
// If the new item is the same as the recently deleted one (i.e. a drag/drop event)
// then cancel the deletion and reuse the ContentPresenter so it doesn't have to be
// redrawn. We do need to link the presenter to the new item though (using the Tag)
ContentPresenter cp = FindChildContentPresenter(_deletedObject);
if (cp != null)
{
int index = _itemsHolder.Children.IndexOf(cp);
(_itemsHolder.Children[index] as ContentPresenter).Tag =
(item is TabItem) ? item : (this.ItemContainerGenerator.ContainerFromItem(item));
}
_deletedObject = null;
}
}
}
if (e.OldItems != null)
{
foreach (var item in e.OldItems)
{
_deletedObject = item;
// We want to run this at a slightly later priority in case this
// is a drag/drop operation so that we can reuse the template
this.Dispatcher.BeginInvoke(DispatcherPriority.DataBind,
new Action(delegate()
{
if (_deletedObject != null)
{
ContentPresenter cp = FindChildContentPresenter(_deletedObject);
if (cp != null)
{
this._itemsHolder.Children.Remove(cp);
}
}
}
));
}
}
UpdateSelectedItem();
break;
case NotifyCollectionChangedAction.Replace:
throw new NotImplementedException("Replace not implemented yet");
}
}
/// <summary>
/// update the visible child in the ItemsHolder
/// </summary>
/// <param name="e"></param>
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
UpdateSelectedItem();
}
/// <summary>
/// generate a ContentPresenter for the selected item
/// </summary>
void UpdateSelectedItem()
{
if (_itemsHolder == null)
{
return;
}
// generate a ContentPresenter if necessary
TabItem item = GetSelectedTabItem();
if (item != null)
{
CreateChildContentPresenter(item);
}
// show the right child
foreach (ContentPresenter child in _itemsHolder.Children)
{
child.Visibility = ((child.Tag as TabItem).IsSelected) ? Visibility.Visible : Visibility.Collapsed;
}
}
/// <summary>
/// create the child ContentPresenter for the given item (could be data or a TabItem)
/// </summary>
/// <param name="item"></param>
/// <returns></returns>
ContentPresenter CreateChildContentPresenter(object item)
{
if (item == null)
{
return null;
}
ContentPresenter cp = FindChildContentPresenter(item);
if (cp != null)
{
return cp;
}
// the actual child to be added. cp.Tag is a reference to the TabItem
cp = new ContentPresenter();
cp.Content = (item is TabItem) ? (item as TabItem).Content : item;
cp.ContentTemplate = this.SelectedContentTemplate;
cp.ContentTemplateSelector = this.SelectedContentTemplateSelector;
cp.ContentStringFormat = this.SelectedContentStringFormat;
cp.Visibility = Visibility.Collapsed;
cp.Tag = (item is TabItem) ? item : (this.ItemContainerGenerator.ContainerFromItem(item));
_itemsHolder.Children.Add(cp);
return cp;
}
/// <summary>
/// Find the CP for the given object. data could be a TabItem or a piece of data
/// </summary>
/// <param name="data"></param>
/// <returns></returns>
ContentPresenter FindChildContentPresenter(object data)
{
if (data is TabItem)
{
data = (data as TabItem).Content;
}
if (data == null)
{
return null;
}
if (_itemsHolder == null)
{
return null;
}
foreach (ContentPresenter cp in _itemsHolder.Children)
{
if (cp.Content == data)
{
return cp;
}
}
return null;
}
/// <summary>
/// copied from TabControl; wish it were protected in that class instead of private
/// </summary>
/// <returns></returns>
protected TabItem GetSelectedTabItem()
{
object selectedItem = base.SelectedItem;
if (selectedItem == null)
{
return null;
}
if (_deletedObject == selectedItem)
{
}
TabItem item = selectedItem as TabItem;
if (item == null)
{
item = base.ItemContainerGenerator.ContainerFromIndex(base.SelectedIndex) as TabItem;
}
return item;
}
}
我经常使用的TabControl模板看起来像这样：
<Style x:Key="TabControlEx_NoHeadersStyle" TargetType="{x:Type local:TabControlEx}">
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type localControls:TabControlEx}">
<DockPanel>
<!-- This is needed to draw TabControls with Bound items -->
<StackPanel IsItemsHost="True" Height="0" Width="0" />
<Grid x:Name="PART_ItemsHolder" />
</DockPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
您还可以使用隐式DataTemplate而不是ItemTemplate来简化您的XAML，因为您的ViewModel将放置在TabItem.Content中。我也不太确定你对标题的询问，但如果我理解你的话，你可以在TabItem
<Window.Resources>
<DataTemplate DataType="{x:Type CustomerViewModel}">
<workspace:CustomerWorkspace />
</DataTemplate>
</Window.Resources>
<TabControl ItemsSource="{Binding Workspaces}">
<TabControl.Resources>
<Style TargetType="{x:Type TabItem}">
<Setter Property="Header" Value="{Binding HeaderProperty}" />
</Style>
</TabControl.Resources>
</TabControl>