从重建它的孩子停止的TabControl [英] Stop TabControl from recreating its children
问题描述
我有一个绑定到的TabControl 的ViewModels的的IList 。这的IList 不会随生命周期改变的TabControl 。
I have an IList of viewmodels which are bound to a TabControl. This IList will not change over the lifetime of the TabControl.
<TabControl ItemsSource="{Binding Tabs}" SelectedIndex="0" >
<TabControl.ItemContainerStyle>
<Style TargetType="TabItem">
<Setter Property="Content" Value="{Binding}" />
</Style>
</TabControl.ItemContainerStyle>
</TabControl>
每个视图模型有一个的DataTemplate 这是在指定的 ResourceDictionary中。
Each viewmodel has a DataTemplate which is specified in a ResourceDictionary.
<DataTemplate TargetType={x:Type vm:MyViewModel}>
<v:MyView/>
</DataTemplate>
每个在指定的DataTemplate的意见是资源密集型足以创造，我宁愿创建每个视图只有一次，但是当我切换标签，相关视图的构造函数被调用。从我已阅读，这是预期的行为的TabControl ，但我不明白的机制是什么它调用构造函数。
Each of the views specified in the DataTemplate are resource intensive enough to create that I would rather create each view just once, but when I switch tabs, the constructor for the relevant view is called. From what I have read, this is the expected behavior for the TabControl, but it is not clear to me what the mechanism is which calls the constructor.
我已经采取了看<一个href=\"http://stackoverflow.com/questions/2080764/how-to-$p$pserve-control-state-within-tab-items-in-a-tabcontrol\">a它采用用户控件取值但解决方案提供有需要我类似的问题，绑定到的意见，这是不可取。
I have taken a look at a similar question which uses UserControls but the solution offered there would require me to bind to views which is undesirable.
推荐答案
默认情况下，的TabControl 共用一个小组来呈现它的内容。做你想要什么（和许多其他开发商WPF），您需要扩展的TabControl 像这样：
By default, the TabControl shares a panel to render it's content. To do what you want (and many other WPF developers), you need to extend TabControl like so:
TabControlEx.cs
[TemplatePart(Name = "PART_ItemsHolder", Type = typeof(Panel))]
public class TabControlEx : TabControl
{
private Panel ItemsHolderPanel = null;
public TabControlEx()
: base()
{
// This is necessary so that we get the initial databound selected item
ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;
}
/// <summary>
/// If containers are done, generate the selected item
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private 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();
ItemsHolderPanel = 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 (ItemsHolderPanel == null)
return;
switch (e.Action)
{
case NotifyCollectionChangedAction.Reset:
ItemsHolderPanel.Children.Clear();
break;
case NotifyCollectionChangedAction.Add:
case NotifyCollectionChangedAction.Remove:
if (e.OldItems != null)
{
foreach (var item in e.OldItems)
{
ContentPresenter cp = FindChildContentPresenter(item);
if (cp != null)
ItemsHolderPanel.Children.Remove(cp);
}
}
// Don't do anything with new items because we don't want to
// create visuals that aren't being shown
UpdateSelectedItem();
break;
case NotifyCollectionChangedAction.Replace:
throw new NotImplementedException("Replace not implemented yet");
}
}
protected override void OnSelectionChanged(SelectionChangedEventArgs e)
{
base.OnSelectionChanged(e);
UpdateSelectedItem();
}
private void UpdateSelectedItem()
{
if (ItemsHolderPanel == null)
return;
// Generate a ContentPresenter if necessary
TabItem item = GetSelectedTabItem();
if (item != null)
CreateChildContentPresenter(item);
// show the right child
foreach (ContentPresenter child in ItemsHolderPanel.Children)
child.Visibility = ((child.Tag as TabItem).IsSelected) ? Visibility.Visible : Visibility.Collapsed;
}
private 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));
ItemsHolderPanel.Children.Add(cp);
return cp;
}
private ContentPresenter FindChildContentPresenter(object data)
{
if (data is TabItem)
data = (data as TabItem).Content;
if (data == null)
return null;
if (ItemsHolderPanel == null)
return null;
foreach (ContentPresenter cp in ItemsHolderPanel.Children)
{
if (cp.Content == data)
return cp;
}
return null;
}
protected TabItem GetSelectedTabItem()
{
object selectedItem = base.SelectedItem;
if (selectedItem == null)
return null;
TabItem item = selectedItem as TabItem;
if (item == null)
item = base.ItemContainerGenerator.ContainerFromIndex(base.SelectedIndex) as TabItem;
return item;
}
}
XAML
<Style TargetType="{x:Type controls:TabControlEx}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TabControl}">
<Grid Background="{TemplateBinding Background}" ClipToBounds="True" KeyboardNavigation.TabNavigation="Local" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition x:Name="ColumnDefinition0" />
<ColumnDefinition x:Name="ColumnDefinition1" Width="0" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition x:Name="RowDefinition0" Height="Auto" />
<RowDefinition x:Name="RowDefinition1" Height="*" />
</Grid.RowDefinitions>
<DockPanel Margin="2,2,0,0" LastChildFill="False">
<TabPanel x:Name="HeaderPanel" Margin="0,0,0,-1" VerticalAlignment="Bottom" Panel.ZIndex="1" DockPanel.Dock="Right"
IsItemsHost="True" KeyboardNavigation.TabIndex="1" />
</DockPanel>
<Border x:Name="ContentPanel" Grid.Row="1" Grid.Column="0"
Background="{TemplateBinding Foreground}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}"
KeyboardNavigation.DirectionalNavigation="Contained" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local">
<Grid x:Name="PART_ItemsHolder" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
注意：我没有想出这个解决方案。它的编程论坛上分享了好几年，并认为它是现在那些WPF的食谱书籍之一。最古老的或原始来源我相信这是<一个href=\"http://www.pluralsight-training.net/community/blogs/eburke/archive/2009/04/30/keeping-the-wpf-tab-control-from-destroying-its-children.aspx\">PluralSight .NET博客文章并在计算器上这答案。
Note: I did not come up with this solution. It has been shared in programming forums for several years and believe that it is in now one of those WPF recipes books. The oldest or original source for I believe was PluralSight .NET blog post and this answer on StackOverflow.
HTH，
这篇关于从重建它的孩子停止的TabControl的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
