WPF TabControl-防止标签更改时卸载?

我在这里找到了一个解决方法: https://web.archive.org/web/20120429044747/http://eric.burke.name/dotnetmania/2009/04/26/22.09.28

这是正确的链接: http://web.archive.org/web/20110825185059/http://eric.burke.name/dotnetmania/2009/04/26/22.09.28

它基本上存储选项卡的ContentPresenter,并在切换选项卡时加载它,而不是重新绘制它。由于这是一个删除/添加操作,所以在拖放选项卡时仍然会导致延迟,但是经过一些修改,我也消除了这种情况(以较低的调度程序优先级运行删除代码,然后运行添加代码,因此添加操作有机会取消删除操作,并使用旧的ContentPresenter而不是绘图)一个新的)

上面的链接似乎不再工作,所以我将粘贴一个代码的副本在这里。它被修改了一点以允许拖放,但是它仍然应该以相同的方式工作。

using System;
using System.Windows;
using System.Windows.Threading;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Collections.Specialized;

// 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;
    }
}

除此之外,我还遇到了一个类似的问题,并通过缓存一个表示代码中tab项内容的用户控件来解决了这个问题。

在我的项目中,我有一个绑定到集合(MVVM)的选项卡控件。但是,第一个选项卡是一个概述,显示列表视图中所有其他选项卡的摘要。我遇到的问题是,每当用户将所选内容从“项目”选项卡移动到“概述”选项卡时,都会使用所有摘要数据重新绘制概述,这可能需要10-15秒,具体时间取决于集合中的项目数。(请注意,它们不是从db或任何东西中重新加载实际数据,而是纯粹的摘要视图的绘制过程)。

我想要的是,这个摘要视图的加载只在第一次加载数据上下文时发生一次,随后在选项卡之间的任何切换都是瞬时的。

解决方案:

涉及的类别: 主窗口.xaml-包含选项卡控件的主页面。 主窗口.xaml.cs-上面的代码。 概述.xaml-用于绘制“概述”选项卡项内容的用户控件。

步骤:

1. 替换'主窗口.xaml'绘制带有名为'OverviewPlaceholder'的空白用户控件的overview选项卡项'

2. 将“OverviewModel”的引用设置为“public within”主窗口视图模型.cs'

4. 将事件处理程序添加到用户控件“OverviewPlaceholder”的已加载事件中,在此方法中,仅当“Overview”为null时才实例化静态引用,将此引用的datacontext设置为当前datacontext(即“MainWindowViewModel”)中的“OverviewModel”引用,并将占位符的内容设置为“概述”的静态引用。

现在只绘制一次overview页面,因为每次加载它(即用户单击overview选项卡)时,它都会将已经呈现的静态用户控件放回页面上。

我有一个非常简单的解决方案,避免在标签更改时重新加载标签, 在tabItem中使用contentPresenter,而不是content属性。

e、 g.(MVVM样式)

代替

      <TabItem Header="Tab1" Content="{Binding Tab1ViewModel}" />

        <TabItem Header="Tab1">
            <ContentPresenter Content="{Binding Tab1ViewModel}" />
        </TabItem>