我正在尝试创建一个用户控件来代表我所说的工作区(引用自 Josh Smith 的博客)。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 excal 工作簿的浏览器中一样。
每次用户打开新工作区时，该工作区都应显示在选项卡控件中。每个工作区都采用用户控件的形式，每个工作区都有自己的 View 模型。我希望 Tab Header 显示我的 View 模型中的属性，我认为这可能必须通过我的用户控件作为属性公开。
到目前为止，在我遇到许多问题之前，我最喜欢的最干净的解决方案是使用数据模板。基本上我做了以下事情:
<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(bind)到一个包含我所有工作区的 observablecollection(对象)。
这很好用，除了两件事:
如果我打开多个客户，那么我会打开多个工作区。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。所以所有未绑定(bind)的东西都会失去状态。
不同工作区(使用不同数据模板)之间的交换性能非常慢。
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 并放弃数据模板。现在解决了丢失状态的问题之一。然而，现在我面临着两个遗留问题:
- 如何在不使用 DataTemplate 的情况下设置 TabItem.Header 属性
- 在选项卡之间来回切换的速度仍然很慢，除非它们属于相同的 DataTemplate。
然后我继续实际将 TabItem 添加到代码隐藏中的 ObservableCollection，并将 TabItem.Content 属性设置为用户控件的属性。速度问题和丢失状态问题现在都已消除，因为我已经删除了 DataTemplates 的使用。但是，我现在遇到了将 TabItem.header 绑定(bind)到应该显示在选项卡标题中的用户控件的自定义“标题”属性的问题。
所以在这篇非常长的帖子之后，我的问题是:
有什么方法可以使用数据模板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.有没有比我在上面的帖子中提到的更好的选择？
有没有办法通过 Xaml 而不是通过标签项的后端代码构造来完成所有这些工作？
最佳答案
WPF 的默认行为是卸载不可见的项，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(bind)的内容(例如滚动位置、控件状态等)都将被重置。
有个好网站here其中包含用于扩展 TabControl 并阻止其在切换选项卡时破坏其 TabItems 的代码，但它现在似乎不再存在。
这是代码的副本，尽管我对其进行了一些更改。它在切换标签时保留 TabItems 的 ContentPresenter，并在您返回页面时使用它重绘 TabItem。它会占用更多内存，但我发现它在性能上更好，因为 TabItem 不再需要重新创建其上的所有控件。
// 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;
}
}
我通常使用的 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>
您还可以通过使用隐式 DataTemplate 而不是 ItemTemplate 来简化您的 XAML，因为您的 ViewModel 将放置在您的 TabItem.Content 中.我也不太确定你在问什么标题，但如果我理解正确，你可以为 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>
关于wpf - 绑定(bind)到 WPF 中 TabControl 的 ItemsSource，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12432062/