我在一个窗口中有几个自定义用户控件。它们会动态出现,就像工作区一样。 我需要在itemscontrol上添加一个依赖属性,以便在向绑定的observable集合添加项目时触发下滚,就像这样: (usercontrol)
<ScrollViewer VerticalScrollBarVisibility="Auto" >
<ItemsControl Grid.Row="0" ItemsSource="{Binding Messages}" View:ItemsControlBehavior.ScrollOnNewItem="True">
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBox IsReadOnly="True" TextWrapping="Wrap" Text="{Binding Path=DataContext, RelativeSource={RelativeSource Self}}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
我的依赖属性代码如下:
public class ItemsControlBehavior
{
static readonly Dictionary<ItemsControl, Capture> Associations =
new Dictionary<ItemsControl, Capture>();
public static bool GetScrollOnNewItem(DependencyObject obj)
{
return (bool)obj.GetValue(ScrollOnNewItemProperty);
}
public static void SetScrollOnNewItem(DependencyObject obj, bool value)
{
obj.SetValue(ScrollOnNewItemProperty, value);
}
public static readonly DependencyProperty ScrollOnNewItemProperty =
DependencyProperty.RegisterAttached(
"ScrollOnNewItem",
typeof(bool),
typeof(ItemsControl),
new UIPropertyMetadata(false, OnScrollOnNewItemChanged));
public static void OnScrollOnNewItemChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var mycontrol = d as ItemsControl;
if (mycontrol == null) return;
bool newValue = (bool)e.NewValue;
if (newValue)
{
mycontrol.Loaded += new RoutedEventHandler(MyControl_Loaded);
mycontrol.Unloaded += new RoutedEventHandler(MyControl_Unloaded);
}
else
{
mycontrol.Loaded -= MyControl_Loaded;
mycontrol.Unloaded -= MyControl_Unloaded;
if (Associations.ContainsKey(mycontrol))
Associations[mycontrol].Dispose();
}
}
static void MyControl_Unloaded(object sender, RoutedEventArgs e)
{
var mycontrol = (ItemsControl)sender;
Associations[mycontrol].Dispose();
mycontrol.Unloaded -= MyControl_Unloaded;
}
static void MyControl_Loaded(object sender, RoutedEventArgs e)
{
var mycontrol = (ItemsControl)sender;
var incc = mycontrol.Items as INotifyCollectionChanged;
if (incc == null) return;
mycontrol.Loaded -= MyControl_Loaded;
Associations[mycontrol] = new Capture(mycontrol);
}
class Capture : IDisposable
{
public ItemsControl mycontrol{ get; set; }
public INotifyCollectionChanged incc { get; set; }
public Capture(ItemsControl mycontrol)
{
this.mycontrol = mycontrol;
incc = mycontrol.ItemsSource as INotifyCollectionChanged;
incc.CollectionChanged +=incc_CollectionChanged;
}
void incc_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
ScrollViewer sv = mycontrol.Parent as ScrollViewer;
sv.ScrollToBottom();
}
}
public void Dispose()
{
incc.CollectionChanged -= incc_CollectionChanged;
}
}
}
在我用户控件的首次实例化过程中,它表现得非常出色。但当另一个相同类型的用户控件被动态实例化时,依赖属性就再也不能正确地附加到我的滚动视图器上了。只有第一个实例将正常工作。
我知道依赖属性是静态的,但这是否意味着它们不能同时在添加到窗口的几个相同类型的用户控件上起作用?
更新02/03:这是我如何将viewmodel设置为视图(而不是通过编程):
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="clr-namespace:testDp.ViewModel"
xmlns:View="clr-namespace:testDp.View">
<DataTemplate DataType="{x:Type vm:ChatTabViewModel}">
<View:ChatTabView />
</DataTemplate>
</ResourceDictionary>
即使在datatemplate标签中设置x:shared = false,它也不能工作。 但是如果我像传统的方式一样设置数据上下文,比如usercontrol.datacontext = new viewmodel(),它肯定会起作用。但是建议使用“共享”视图,那么我们如何让依赖属性与这种“xaml”方式的数据上下文设置方式一起工作呢?