Question

我正在使用语义缩放控件来显示WinRT应用程序中的联系人列表。当我手动滚动列表时，我想获取视图中的当前项目（视图中将有多个项目，但我想获得最近的视图中的项目）。因此，当用户导航回此联系人列表时，我可以保存滚动位置以将其设置为原样。有什么建议吗？我尝试获取当前的选定索引，但在滚动列表时从未更新过：

int lastViewedItem = ((ListViewBase)this.semanticZoom.ZoomedInView).SelectedIndex;

导航回来

(ListViewBase)this.semanticZoom.ZoomedInView).SelectedIndex = lastViewedItem;

 ((ListViewBase)this.semanticZoom.ZoomedInView).ScrollIntoView(((ListViewBase)this.semanticZoom.ZoomedInView).SelectedItem);

Answer 1

我已经为我认识here的任何已知ItemsControl创建了一个扩展程序。

using System;
using System.Collections;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;

/// <summary>
/// Gets the first visible element.
/// </summary>
/// <param name="itemsControl">The ItemsControl.</param>
/// <returns>The first visible item or null if not found.</returns>
public static object GetFirstVisibleItem(this ItemsControl itemsControl)
{
    var index = GetFirstVisibleIndex(itemsControl);

    if (index == -1)
    {
        return null;
    }

    var list = itemsControl.ItemsSource as IList;

    if (itemsControl.ItemsSource != null &&
        list != null &&
        list.Count > index)
    {
        return list[index];
    }

    if (itemsControl.Items != null &&
        itemsControl.Items.Count > index)
    {
        return itemsControl.Items[index];
    }

    throw new InvalidOperationException();
}

/// <summary>
/// Gets the index of the first visible element.
/// </summary>
/// <param name="itemsControl">The ItemsControl.</param>
/// <returns>The index of the first visible item or -1 if not found.</returns>
public static int GetFirstVisibleIndex(this ItemsControl itemsControl)
{
    // First checking if no items source or an empty one is used
    if (itemsControl.ItemsSource == null)
    {
        return -1;
    }

    var enumItemsSource = itemsControl.ItemsSource as IEnumerable;

    if (enumItemsSource != null && !enumItemsSource.GetEnumerator().MoveNext())
    {
        return -1;
    }

    // Check if a modern panel is used as an items panel
    var sourcePanel = itemsControl.ItemsPanelRoot;

    if (sourcePanel == null)
    {
        throw new InvalidOperationException("Can't get first visible index from an ItemsControl with no ItemsPanel.");
    }

    var isp = sourcePanel as ItemsStackPanel;

    if (isp != null)
    {
        return isp.FirstVisibleIndex;
    }

    var iwg = sourcePanel as ItemsWrapGrid;

    if (iwg != null)
    {
        return iwg.FirstVisibleIndex;
    }

    // Check containers for first one in view
    if (sourcePanel.Children.Count == 0)
    {
        return -1;
    }

    if (itemsControl.ActualWidth == 0)
    {
        throw new InvalidOperationException("Can't get first visible index from an ItemsControl that is not loaded or has zero size.");
    }

    for (int i = 0; i < sourcePanel.Children.Count; i++)
    {
        var container = (FrameworkElement)sourcePanel.Children[i];
        var bounds = container.TransformToVisual(itemsControl).TransformBounds(new Rect(0, 0, container.ActualWidth, container.ActualHeight));

        if (bounds.Left < itemsControl.ActualWidth &&
            bounds.Top < itemsControl.ActualHeight &&
            bounds.Right > 0 &&
            bounds.Bottom > 0)
        {
            return itemsControl.IndexFromContainer(container);
        }
    }

    throw new InvalidOperationException();
}

如何在语义缩放控件中查看当前项目

1 个答案: