使用 MVVM 将 ScrollIntoView 滚动到 SelectedItem (Windows Phone 8.1)答案

【问题标题】：ScrollIntoView to SelectedItem with MVVM (Windows Phone 8.1)使用 MVVM 将 ScrollIntoView 滚动到 SelectedItem (Windows Phone 8.1)
【发布时间】：2016-03-05 12:06:57
【问题描述】：

后面的代码是由

完成的

 ActivityList.ScrollIntoView(ActivityList.SelectedItem);

当您从详细信息页面返回时，当您从详细信息页面返回时，您不必从 ListView 的顶部开始。

有几个示例可以滚动到 ListView 的末尾，但不能滚动到 SelectedItem。

但是这在 MVVM 中是如何完成的呢？使用行为 SDK 创建行为？怎么做？

【问题讨论】：

标签： xaml listview mvvm windows-phone-8.1

【解决方案1】：

我已经使用附加属性（行为）完成了此操作。此行为在名为 DataGridExtensions 的 class 中，如下所示：

public static readonly DependencyProperty ScrollSelectionIntoViewProperty = DependencyProperty.RegisterAttached(
    "ScrollSelectionIntoView", typeof(bool), typeof(DataGridExtensions), new PropertyMetadata(false, ScrollSelectionIntoViewChanged));

private static void ScrollSelectionIntoViewChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    DataGrid dataGrid = d as DataGrid;
    if (dataGrid == null)
        return;

    if (e.NewValue is bool && (bool)e.NewValue)
        dataGrid.SelectionChanged += DataGridOnSelectionChanged;
    else
        dataGrid.SelectionChanged -= DataGridOnSelectionChanged;
}

private static void DataGridOnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    if (e.AddedItems == null || e.AddedItems.Count == 0)
        return;

    DataGrid dataGrid = sender as DataGrid;
    if (dataGrid == null)
        return;

    ScrollViewer scrollViewer = UIHelper.FindChildren<ScrollViewer>(dataGrid).FirstOrDefault();
    if (scrollViewer != null)
    {
        dataGrid.ScrollIntoView(e.AddedItems[0]);
    }
}

public static void SetScrollSelectionIntoView(DependencyObject element, bool value)
{
    element.SetValue(ScrollSelectionIntoViewProperty, value);
}

public static bool GetScrollSelectionIntoView(DependencyObject element)
{
    return (bool)element.GetValue(ScrollSelectionIntoViewProperty);
}

UIHelper.FindChildren的代码是：

public static IList<T> FindChildren<T>(DependencyObject element) where T : FrameworkElement
{
    List<T> retval = new List<T>();
    for (int counter = 0; counter < VisualTreeHelper.GetChildrenCount(element); counter++)
    {
        FrameworkElement toadd = VisualTreeHelper.GetChild(element, counter) as FrameworkElement;
        if (toadd != null)
        {
            T correctlyTyped = toadd as T;
            if (correctlyTyped != null)
            {
                retval.Add(correctlyTyped);
            }
            else
            {
                retval.AddRange(FindChildren<T>(toadd));
            }
        }
    }
    return retval;
}

【讨论】：