WPF 无法使 ItemContainerGenerator.ContainerFromItem 工作

Question

我看过here和 here和许多其他地方，但我似乎无法让 ItemContainerGenerator.ContainerFromItem 方法在 WPF TreeView 上工作!我试图传递我想看到的实际项目，但没有得到任何结果，我只是试图在我的 TreeView 中获取第一个项目。这是我的示例代码:

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，我已尝试调用许多“更新”方法来尝试使 TreeView 变得“可见”和“可访问”。第 22 条军规似乎是你不能使用 ContainerFromItem() 除非第一个 TreeViewItem 被展开，但我不能捕获 TreeViewItem 展开它直到 ContainerFromItem() 有效!

发生的另一件有趣的事情是:当我打开这个窗口(它是一个 UserControl)时，ContainerFromItem() 返回空值，但是如果我关闭窗口并重新打开它，ContainerFromItem() 开始返回非空值。有没有我应该寻找或强制触发的事件？

Answer 1

原来我正在寻找的事件是“已加载”。我只是将一个事件处理程序附加到 XAML 中的 TreeView ，并在该事件处理程序中调用我的逻辑。

<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;
}

希望这对某人有帮助。有时在现实世界中，面对要求苛刻的客户、怪异的要求和紧迫的期限，你得动手了!