WPF无法使ItemContainerGenerator.ContainerFromItem工作

Question

我看过here和here以及许多其他地方，但我似乎无法让ItemContainerGenerator.ContainerFromItem方法在WPF TreeView上工作！我试图传递我想要看到的实际项目，但是没有取得任何进展，我只是尝试在我的TreeView中获得第一个项目。下面是我的示例代码：

private static bool ExpandAndSelectItem(ItemsControl parentContainer, object itemToSelect)
{
    // This doesn't work.
    parentContainer.BringIntoView();
    // May be virtualized, bring into view and try again.
    parentContainer.UpdateLayout();
    parentContainer.ApplyTemplate();

    TreeViewItem topItem = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(parentContainer.Items[0]);

    // Can't find child container unless the parent node is Expanded once
    if ((topItem != null) && !topItem.IsExpanded) 
    {
        topItem.IsExpanded = true;
        parentContainer.UpdateLayout();
    }
}

如您所见，我试图调用许多“更新”方法，以使TreeView成为“可见的”和“可访问的”。问题是，除非第一个ContainerFromItem()是展开的，否则您就不能使用TreeViewItem，但是在ContainerFromItem()工作之前，我无法抓取TreeViewItem来扩展它！

另一件有趣的事情是:当我打开这个窗口(它是一个UserControl)时，ContainerFromItem()返回空，但是如果我关闭窗口并重新打开它，ContainerFromItem()将开始返回非空。有什么事件我应该寻找或强迫开火吗？

Answer 1

原来我要找的那件事是“装好的”。我只是在XAML中将一个事件处理程序附加到我的treeview上，并在该事件处理程序中调用了我的逻辑。

<TreeView x:Name="MyTreeView"
          Margin="0,5,0,5"
          HorizontalAlignment="Left"
          BorderThickness="0"
          FontSize="18"
          FontFamily="Segoe WP"
          MaxWidth="900"
          Focusable="True"
          Loaded="MyTreeView_Load">
    ...
</TreeView>

事件处理程序：

private void MyTreeView_Load(object sender, RoutedEventArgs e)
{
    ShowSelectedThing(MyTreeView, ThingToFind);
}
// Gotta call the TreeView an ItemsControl to cast it between TreeView and TreeViewItem
// as you recurse
private static bool ShowSelectedThing(ItemsControl parentContainer, object ThingToFind)
{
    // check current level of tree
    foreach (object item in parentContainer.Items)
    {
        TreeViewItem currentContainer = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(item);
        if ((currentContainer != null) && (item == ThingToFind)
        {
            currentContainer.IsSelected = true;
            currentContainer.BringIntoView();
            return true;
        }
    }
    // item is not found at current level, check the kids
    foreach (object item in parentContainer.Items)
    {
        TreeViewItem currentContainer = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(item);
        if ((currentContainer != null) && (currentContainer.Items.Count > 0))
        {
            // Have to expand the currentContainer or you can't look at the children
            currentContainer.IsExpanded = true;
            currentContainer.UpdateLayout();
            if (!ShowSelectedThing(currentContainer, ThingToFind))
            {
                // Haven't found the thing, so collapse it back
                currentContainer.IsExpanded = false;
            }
            else
            {
                // We found the thing
                return true;
            }
        }
    }
    // default
    return false;
}

希望这能帮上忙。有时候在现实世界里，有着苛刻的客户，奇怪的要求和很短的截止时间，你必须要黑！

Answer 2

当容器生成器的状态为“NotStarted”或“ContainersGenerating”时，您将找不到容器。

使用此方法查找数据项的容器。

    private static async Task<TreeViewItem> FindItemContainer(ItemsControl itemsControl, object item)
    {
        var generator = itemsControl.ItemContainerGenerator;
        if (generator.Status != GeneratorStatus.ContainersGenerated)
        {
            var tcs = new TaskCompletionSource<object>();
            EventHandler handler = null;
            handler = (s, e) =>
            {
                if (generator.Status == GeneratorStatus.ContainersGenerated)
                {
                    generator.StatusChanged -= handler;
                    tcs.SetResult(null);
                }
                else if (generator.Status == GeneratorStatus.Error)
                {
                    generator.StatusChanged -= handler;
                    tcs.SetException(new InvalidOperationException());
                }
            };
            generator.StatusChanged += handler;
            if (itemsControl is TreeViewItem tvi)
                tvi.IsExpanded = true;
            itemsControl.UpdateLayout();
            await tcs.Task;
        }

        var container = (TreeViewItem)generator.ContainerFromItem(item);
        if(container == null)
        {
            foreach (var parentItem in itemsControl.Items)
            {
                var parentContainer = (TreeViewItem)generator.ContainerFromItem(parentItem);
                container = await FindItemContainer(parentContainer, item);
                if (container != null)
                    return container;
            }
        }
        return container;
    }