ScrollIntoView - 项目不应从视图中消失

从一开始我就想说，我将向能够帮助我解决问题的人颁发 200 赏金。

这是我的简单代码（带有 WPF 的 C#）：

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    /// 

    public partial class Window1 : Window
    {
        string fixedItem;

        public Window1()
        {
            InitializeComponent();
            listBox1.ItemContainerGenerator.ItemsChanged += new System.Windows.Controls.Primitives.ItemsChangedEventHandler(list_changes);

        }



        private void list_changes(object sender, System.Windows.Controls.Primitives.ItemsChangedEventArgs e)
        {
            listBox1.ScrollIntoView(fixedItem);
        }

        private void listBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {      
            fixedItem = (string)listBox1.SelectedItem;        
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Add("item0");
            listBox1.Items.Add("item1");
            listBox1.Items.Add("item2");
            listBox1.Items.Add("item3");
            listBox1.Items.Add("item4");
            listBox1.Items.Add("item5");
            listBox1.Items.Add("item6");

        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Insert(0, "item7");
            listBox1.Items.Insert(0, "item8");
            listBox1.Items.Insert(0, "item9");
            listBox1.Items.Insert(0, "item10");
            listBox1.Items.Insert(0, "item11");
            listBox1.Items.Insert(0, "item12");
            listBox1.Items.Insert(0, "item13");
            listBox1.Items.Insert(0, "item14");
            listBox1.Items.Insert(0, "item15");
        }

        private void button3_Click(object sender, RoutedEventArgs e)
        {
            listBox1.Items.Insert(0, "item16");
            listBox1.Items.Insert(0, "item17");
            listBox1.Items.Insert(0, "item18");
            listBox1.Items.Insert(0, "item19");
            listBox1.Items.Insert(0, "item20");
            listBox1.Items.Insert(0, "item21");
            listBox1.Items.Insert(0, "item22");
            listBox1.Items.Insert(0, "item23");
            listBox1.Items.Insert(0, "item24");
        }
    }
}

首先，我只制作了 3 个按钮来在列表框中插入一些文本。假设我单击按钮 1 和按钮 2，我将得到以下列表：

item15
item14
item13
item12
......
item7
item0
item1
.....
item6

之后，我想单击“项目 12”，然后当我单击按钮 3 时，我希望我的“项目 12”在生成文本时保留在同一位置（列表中的第四个位置）。
简而言之，每次我单击项目时，我希望它在生成文本时保持在完全相同的位置。

那么有人知道如何做到这一点吗？我是否需要使用 ScrollViewer 对象来处理 VerticallOffset 和 ViewportHeigth ？当我单击该项目然后生成文本时，我发布了这个简单的代码，它将将该项目移动到底部（可见位置）并保留在那里。但我根本不想动它。

Edit:

好的，我尝试了这段代码here http://blogs.msdn.com/b/delay/archive/2009/04/19/fewer-gotchas-to-getcha-enhancing-the-scrollintoviewcentered-method-for-wpf-s-listbox.aspx:

FrameworkElement container = listRadioItems.ItemContainerGenerator.ContainerFromItem(fixedItem) as FrameworkElement;

            if (null != container)
            {
                if (ScrollViewer.GetCanContentScroll(listBox))
                {
                    IScrollInfo scrollInfo = VisualTreeHelper.GetParent(container) as IScrollInfo;
                    if (null != scrollInfo)
                    {
                        StackPanel stackPanel = scrollInfo as StackPanel;
                        VirtualizingStackPanel virtualizingStackpanel = scrollInfo as VirtualizingStackPanel;

                        int index = listBox.ItemContainerGenerator.IndexFromContainer(container);

                        if (((null != stackPanel) && (Orientation.Horizontal == stackPanel.Orientation)) || ((null != virtualizingStackpanel) && (Orientation.Horizontal == virtualizingStackpanel.Orientation)))
                        {
                            scrollInfo.SetHorizontalOffset(index - Math.Floor(scrollInfo.ViewportWidth / 2));
                        }
                        else
                        {
                            scrollInfo.SetVerticalOffset(index - Math.Floor(scrollInfo.ViewportHeight / 2));
                        }
                    }
                }
                else
                {
                    Rect rect = new Rect(new Point(), container.RenderSize);

                    FrameworkElement constrainingParent = container;
                    do
                    {
                        constrainingParent = VisualTreeHelper.GetParent(constrainingParent) as FrameworkElement;
                    } while ((null != constrainingParent) && (listBox != constrainingParent) && !(constrainingParent is ScrollContentPresenter));

                    if (null != constrainingParent)
                    {
                        rect.Inflate(Math.Max((constrainingParent.ActualWidth - rect.Width) / 2, 0), Math.Max((constrainingParent.ActualHeight - rect.Height) / 2, 0));
                    }

                    container.BringIntoView(rect);
                }
            }

它对我的作用是将所选项目居中，但滚动向下，只是有时它也会居中。我的问题是，只有有时所选项目才会从视图中消失。

如果我能让项目和滚动都居中，那就太好了。但首先要关心的是该项目不应从视图中消失。

下面是一些代码，用于获取 ListBox 中的第一个可见项目，将这些项目添加到您指定的任何索引，然后在呈现所有新项目后使用调度程序将列表滚动回第一个可见项目。

The ScrollIntoViewTop()扩展方法与您在原始问题中发布的链接相同，但我更改了它以将该项目保留在列表顶部。

The WPFHelpers.IsObjectVisibleInContainer()方法是我过去用来测试对象在另一个容器中是否完全或部分可见的方法。为了获取第一个可见项目，我只需循环遍历 ListBox 项目，获取与每个项目关联的 ListBoxItem 容器，然后检查该容器是否可见。第一个返回 true 的是 ListBox 中的第一个可见项。

这是完整的代码：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    private void button1_Click(object sender, RoutedEventArgs e)
    {
        var firstVisibleItem = GetFirstVisibleItem(listBox1);

        listBox1.Items.Insert(0, "item0");
        listBox1.Items.Insert(0, "item1");
        listBox1.Items.Insert(0, "item2");
        listBox1.Items.Insert(0, "item3");
        listBox1.Items.Insert(0, "item4");
        listBox1.Items.Insert(0, "item5");
        listBox1.Items.Insert(0, "item6");

        if (firstVisibleItem != null)
        {
            Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Loaded,
                new Action(delegate()
                {
                    listBox1.ScrollIntoViewTop(firstVisibleItem);
                }));
        }
    }

    private void button2_Click(object sender, RoutedEventArgs e)
    {
        var firstVisibleItem = GetFirstVisibleItem(listBox1);

        listBox1.Items.Insert(0, "item7");
        listBox1.Items.Insert(0, "item8");
        listBox1.Items.Insert(0, "item9");
        listBox1.Items.Insert(0, "item10");
        listBox1.Items.Insert(0, "item11");
        listBox1.Items.Insert(0, "item12");
        listBox1.Items.Insert(0, "item13");
        listBox1.Items.Insert(0, "item14");
        listBox1.Items.Insert(0, "item15");

        if (firstVisibleItem != null)
        {
            Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Loaded,
                new Action(delegate()
                {
                    listBox1.ScrollIntoViewTop(firstVisibleItem);
                }));
        }
    }

    private void button3_Click(object sender, RoutedEventArgs e)
    {
        var firstVisibleItem = GetFirstVisibleItem(listBox1);

        listBox1.Items.Insert(0, "item16");
        listBox1.Items.Insert(0, "item17");
        listBox1.Items.Insert(0, "item18");
        listBox1.Items.Insert(0, "item19");
        listBox1.Items.Insert(0, "item20");
        listBox1.Items.Insert(0, "item21");
        listBox1.Items.Insert(0, "item22");
        listBox1.Items.Insert(0, "item23");
        listBox1.Items.Insert(0, "item24");

        if (firstVisibleItem != null)
        {
            Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Loaded,
                new Action(delegate()
                {
                    listBox1.ScrollIntoViewTop(firstVisibleItem);
                }));
        }
    }

    private object GetFirstVisibleItem(ListBox listBox)
    {
        foreach (var item in listBox.Items)
        {
            var itemContainer = (ListBoxItem)listBox.ItemContainerGenerator.ContainerFromItem(item);

            if (WPFHelpers.IsObjectVisibleInContainer(itemContainer, listBox) == ControlVisibility.Full)
            {
                return item;
            }
        }

        return null;
    }
}

public enum ControlVisibility
{
    Hidden,
    Partial,
    Full,
    FullHeightPartialWidth,
    FullWidthPartialHeight
}

public class WPFHelpers
{
    /// <summary>
    /// Checks to see if an object is rendered visible within a parent container
    /// </summary>
    /// <param name="child">UI element of child object</param>
    /// <param name="parent">UI Element of parent object</param>
    /// <returns>ControlVisibility Enum: Hidden, Partial or Visible</returns>
    public static ControlVisibility IsObjectVisibleInContainer(FrameworkElement child, UIElement parent)
    {
        GeneralTransform childTransform = child.TransformToAncestor(parent);
        //Rect childSize = childTransform.TransformBounds(new Rect(new Point(0, 0), child.RenderSize));
        Rect childSize = childTransform.TransformBounds(new Rect(new Point(0, 0), new Point(child.ActualWidth, child.ActualHeight)));

        Rect result = Rect.Intersect(new Rect(new Point(0, 0), parent.RenderSize), childSize);
        if (result == Rect.Empty)
        {
            return ControlVisibility.Hidden;
        }
        if (result.Height == childSize.Height && result.Width == childSize.Width)
        {
            return ControlVisibility.Full;
        }
        if (result.Height == childSize.Height)
        {
            return ControlVisibility.FullHeightPartialWidth;
        }
        if (result.Width == childSize.Width)
        {
            return ControlVisibility.FullWidthPartialHeight;
        }
        return ControlVisibility.Partial;
    }
}

/// <summary>
/// Class implementing helpful extensions to ListBox.
/// </summary>
public static class ListBoxExtensions
{
    /// <summary>
    /// Causes the object to scroll into view centered.
    /// </summary>
    /// <param name="listBox">ListBox instance.</param>
    /// <param name="item">Object to scroll.</param>
    //[SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters",
    //    Justification = "Deliberately targeting ListBox.")]
    public static void ScrollIntoViewTop(this ListBox listBox, object item)
    {
        Debug.Assert(!VirtualizingStackPanel.GetIsVirtualizing(listBox),
            "VirtualizingStackPanel.IsVirtualizing must be disabled for ScrollIntoViewCentered to work.");

        // Get the container for the specified item
        var container = listBox.ItemContainerGenerator.ContainerFromItem(item) as FrameworkElement;
        if (null != container)
        {
            if (ScrollViewer.GetCanContentScroll(listBox))
            {
                // Get the parent IScrollInfo
                var scrollInfo = VisualTreeHelper.GetParent(container) as IScrollInfo;
                if (null != scrollInfo)
                {
                    // Need to know orientation, so parent must be a known type
                    var stackPanel = scrollInfo as StackPanel;
                    var virtualizingStackPanel = scrollInfo as VirtualizingStackPanel;
                    Debug.Assert((null != stackPanel) || (null != virtualizingStackPanel),
                        "ItemsPanel must be a StackPanel or VirtualizingStackPanel for ScrollIntoViewCentered to work.");

                    // Get the container's index
                    var index = listBox.ItemContainerGenerator.IndexFromContainer(container);

                    // Center the item by splitting the extra space
                    if (((null != stackPanel) && (Orientation.Horizontal == stackPanel.Orientation)) ||
                        ((null != virtualizingStackPanel) && (Orientation.Horizontal == virtualizingStackPanel.Orientation)))
                    {
                        //scrollInfo.SetHorizontalOffset(index - Math.Floor(scrollInfo.ViewportWidth / 2));
                        scrollInfo.SetHorizontalOffset(index);
                    }
                    else
                    {
                        //scrollInfo.SetVerticalOffset(index - Math.Floor(scrollInfo.ViewportHeight / 2));
                        scrollInfo.SetVerticalOffset(index);
                    }
                }
            }
            else
            {
                // Get the bounds of the item container
                var rect = new Rect(new Point(), container.RenderSize);

                // Find constraining parent (either the nearest ScrollContentPresenter or the ListBox itself)
                FrameworkElement constrainingParent = container;
                do
                {
                    constrainingParent = VisualTreeHelper.GetParent(constrainingParent) as FrameworkElement;
                } while ((null != constrainingParent) &&
                         (listBox != constrainingParent) &&
                         !(constrainingParent is ScrollContentPresenter));

                if (null != constrainingParent)
                {
                    // Inflate rect to fill the constraining parent
                    rect.Inflate(
                        Math.Max((constrainingParent.ActualWidth - rect.Width) / 2, 0),
                        Math.Max((constrainingParent.ActualHeight - rect.Height) / 2, 0));
                }

                // Bring the (inflated) bounds into view
                container.BringIntoView(rect);
            }
        }
    }
}