我有一個IList綁定到的viewmodel TabControl。這IList不會在的使用期限內(nèi)發(fā)生變化TabControl。<TabControl ItemsSource="{Binding Tabs}" SelectedIndex="0" > <TabControl.ItemContainerStyle> <Style TargetType="TabItem"> <Setter Property="Content" Value="{Binding}" /> </Style> </TabControl.ItemContainerStyle></TabControl>每個視圖模型都有一個DataTemplate在中指定的ResourceDictionary。<DataTemplate TargetType={x:Type vm:MyViewModel}> <v:MyView/></DataTemplate>DataTemplate中指定的每個視圖都占用大量資源，以至于我寧愿只創(chuàng)建一次每個視圖，但是當我切換選項卡時，將調(diào)用相關視圖的構造函數(shù)。根據(jù)我的閱讀，這是的預期行為TabControl，但是對我來說，尚不清楚調(diào)用構造函數(shù)的機制是什么。我看過一個類似的問題，它使用了UserControls，但是那里提供的解決方案將需要我綁定到視圖，這是不希望的。
3 回答
紅顏莎娜
TA貢獻1842條經(jīng)驗 獲得超13個贊
默認情況下，TabControl共享面板以呈現(xiàn)其內(nèi)容。若要做您想做的事情（以及許多其他WPF開發(fā)人員），您需要TabControl像這樣進行擴展：
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 Background}"
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：我沒有提出這個解決方案。它已在編程論壇中共享了數(shù)年，并且相信它現(xiàn)在已成為WPF食譜書之一。我認為最古老或原始的來源是PluralSight .NET博客文章，以及StackOverflow上的答案。
qq_花開花謝_0
TA貢獻1835條經(jīng)驗 獲得超7個贊
有一個不是很明顯但很優(yōu)雅的解決方案。主要思想是通過自定義轉(zhuǎn)換器手動生成TabItem的ContentTree的VisualTree屬性。
定義一些資源
<Window.Resources>
<converters:ContentGeneratorConverter x:Key="ContentGeneratorConverter"/>
<DataTemplate x:Key="ItemDataTemplate">
<StackPanel>
<TextBox Text="Try to change this text and choose another tab"/>
<TextBlock Text="{Binding}"/>
</StackPanel>
</DataTemplate>
<markup:Set x:Key="Items">
<system:String>Red</system:String>
<system:String>Green</system:String>
<system:String>Blue</system:String>
</markup:Set>
</Window.Resources>
哪里
public class ContentGeneratorConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var control = new ContentControl {ContentTemplate = (DataTemplate) parameter};
control.SetBinding(ContentControl.ContentProperty, new Binding());
return control;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) =>
throw new NotImplementedException();
}
Set是這樣的
public class Set : List<object> { }
然后改為經(jīng)典使用ContentTemplate屬性
<TabControl
ItemsSource="{StaticResource Items}"
ContentTemplate="{StaticResource ItemDataTemplate}">
</TabControl>
我們應該通過以下方式指定ItemContainerStyle
<TabControl
ItemsSource="{StaticResource Items}">
<TabControl.ItemContainerStyle>
<Style TargetType="TabItem" BasedOn="{StaticResource {x:Type TabItem}}">
<Setter Property="Content" Value="{Binding Converter={StaticResource ContentGeneratorConverter}, ConverterParameter={StaticResource ItemDataTemplate}}"/>
</Style>
</TabControl.ItemContainerStyle>
</TabControl>
現(xiàn)在，嘗試比較兩種變體，以查看選項卡切換期間ItemDataTemplate處TextBox行為的不同。
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