WP8_检测列表是否滑动
One of the UI features of lists on Windows Phone 7 is that the "scroll bars" don't really act like traditional scroll bars; they are non-interactive and they only appear when the list is actually scrolling. To achieve this, the Silverlight team added a new visual state group that is used in the default control template for showing / hiding the scroll bars.
You can get programmatic access to the scroll state with the following approach. First, paste this XAML into the ContentGrid of a new WP7 application:
<ListBox FontSize="50" x:Name="theList">
<ListBoxItem Content="Item 00"/>
<ListBoxItem Content="Item 01"/>
<ListBoxItem Content="Item 02"/>
<ListBoxItem Content="Item 03"/>
<ListBoxItem Content="Item 04"/>
<ListBoxItem Content="Item 05"/>
<ListBoxItem Content="Item 06"/>
<ListBoxItem Content="Item 07"/>
<ListBoxItem Content="Item 08"/>
<ListBoxItem Content="Item 09"/>
<ListBoxItem Content="Item 10"/>
<ListBoxItem Content="Item 11"/>
<ListBoxItem Content="Item 12"/>
<ListBoxItem Content="Item 13"/>
<ListBoxItem Content="Item 14"/>
<ListBoxItem Content="Item 15"/>
<ListBoxItem Content="Item 16"/>
<ListBoxItem Content="Item 17"/>
<ListBoxItem Content="Item 18"/>
<ListBoxItem Content="Item 19"/>
<ListBoxItem Content="Item 20"/>
<ListBoxItem Content="Item 21"/>
<ListBoxItem Content="Item 22"/>
<ListBoxItem Content="Item 23"/>
<ListBoxItem Content="Item 24"/>
<ListBoxItem Content="Item 25"/>
<ListBoxItem Content="Item 26"/>
<ListBoxItem Content="Item 27"/>
<ListBoxItem Content="Item 28"/>
<ListBoxItem Content="Item 29"/>
</ListBox>
Now add the following to the code-behind file:
public MainPage()
{
InitializeComponent();
Loaded += new RoutedEventHandler(MainPage_Loaded);
}bool alreadyHookedScrollEvents = false;
void MainPage_Loaded(object sender, RoutedEventArgs e)
{
if (alreadyHookedScrollEvents)
return;alreadyHookedScrollEvents = true;
ScrollViewer viewer = FindSimpleVisualChild<ScrollViewer>(theList);
if (viewer != null)
{
// Visual States are always on the first child of the control template
FrameworkElement element = VisualTreeHelper.GetChild(viewer, 0) as FrameworkElement;
if (element != null)
{
VisualStateGroup group = FindVisualState(element, "ScrollStates");
if (group != null)
{
group.CurrentStateChanging += (s, args) => PageTitle.Text = args.NewState.Name;
}
}
}
}VisualStateGroup FindVisualState(FrameworkElement element, string name)
{
if (element == null)
return null;IList groups = VisualStateManager.GetVisualStateGroups(element);
foreach (VisualStateGroup group in groups)
if (group.Name == name)
return group;return null;
}T FindSimpleVisualChild<T>(DependencyObject element) where T : class
{
while (element != null)
{if (element is T)
return element as T;element = VisualTreeHelper.GetChild(element, 0);
}return null;
}
What this does is attach to the CurrentStateChanging event of the VisualStateGroup, which will be raised every time the scroll state changes from "Scrolling" to "NotScrolling" or vice-versa. There's a bunch of infrastructure code to walk the visual tree and pull out a state group, but the core code is very simple:
- First we attach a handler called MainPage_Loaded to the Page.Loaded event
- When the page loads, we call FindSimpleVisualChild to get the ScrollViewerchild of the list (this is a pretty dumb function)
- We make sure to only do this once, because the page could get loaded more than once if it is navigated
- Then we call FindVisualState to get the named visual state from the first child of the ScrollViewer
- Then we add a handler to the CurrentStateChanging event
原文作者:Peter Torr - MSFT
原文链接: http://blogs.msdn.com/b/ptorr/archive/2010/07/23/how-to-detect-when-a-list-is-scrolling-or-not.aspx
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