xaml - 使用MVVM将ScrollIntoView转换为SelectedItem(Windows Phone 8.1)

Question

在后面的代码中，这是通过

 ActivityList.ScrollIntoView(ActivityList.SelectedItem);

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

有一些示例可滚动到ListView的末尾，而不滚动到SelectedItem。

但是，如何在MVVM中完成此操作？使用Behavior SDK创建行为？如何？

Answer 1

我已经通过附加属性(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;
}