【发布时间】：2012-02-06 11:27:38
【问题描述】：
按照 mvvm 工作区（客户视图）上的 Josh Smith 示例，我有一个主窗口和一个主窗口视图模型，其中包含“ChatTabViewModel”的 ObservableCollection：
internal class FriendsListViewModel : ObservableObject
{
#region bound properties
private ICollectionView viewfriends;
private ObservableCollection<ChatTabViewModel> _chatTab;
...
#endregion
}
我在 xaml 中有一个专门用于此集合的区域：
<ContentControl Grid.Column="0" Grid.Row="0" Grid.RowSpan="2" Content="{Binding Path=ChatTabs}" ContentTemplate="{StaticResource ChatTabsTemplate}" />
在我的资源字典中：
<DataTemplate DataType="{x:Type vm:ChatTabViewModel}">
<View:ChatTabView />
</DataTemplate>
<DataTemplate x:Key="ClosableTabItemTemplate">
<DockPanel>
<Button
Command="{Binding Path=CloseCommand}"
Content="X"
Cursor="Hand"
DockPanel.Dock="Right"
Focusable="False"
FontFamily="Courier"
FontSize="9"
FontWeight="Bold"
Margin="0,1,0,0"
Padding="0"
VerticalContentAlignment="Bottom"
Width="16" Height="16"
/>
<ContentPresenter
Content="{Binding Path=Caption, Mode=OneWay}"
VerticalAlignment="Center">
</ContentPresenter>
</DockPanel>
</DataTemplate>
<DataTemplate x:Key="ChatTabsTemplate">
<TabControl
IsSynchronizedWithCurrentItem="True"
ItemsSource="{Binding}"
ItemTemplate="{StaticResource ClosableTabItemTemplate}"
Margin="4"/>
</DataTemplate>
在用户事件中，我在我的集合中添加了一个新的 ChattabViewModel，并且与之相关的视图出现在主窗口中。
但是当我尝试在 ChattabView 的滚动条上添加附加属性时，该属性将仅附加在第一个 ChattabViewModel 实例上，其他选项卡不会绑定到附加属性。这是 ChattabView XAML：
<ScrollViewer VerticalScrollBarVisibility="Auto" Grid.Row="0">
<ItemsControl 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>
以及附加属性的代码：
namespace GtalkOntre.View
{
/// <summary>
/// Util class to scroll down when a new message is added.
/// </summary>
/// <remarks>attached property called ScrollOnNewItem that when set to true hooks into the INotifyCollectionChanged events of the itemscontrol items source and upon detecting a new item, scrolls the scrollbar to it.</remarks>
public class ItemsControlBehavior
{
static 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 DependencyProperty ScrollOnNewItemProperty =
DependencyProperty .RegisterAttached(
"ScrollOnNewItem",
typeof(bool),
typeof(ItemsControlBehavior),
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 += MyControl_Loaded;
mycontrol.Unloaded += 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;
}
}
}
}
那么为什么附加属性只绑定一次，在 chattabviewmodel 集合的第一次“chattabview”出现时？因此，仅在第一个 chattabviewmodel 上工作。 当我全部关闭它们时，附加属性将在 chattabviewmodel 的最后一个实例上解除绑定，并且当我添加新的第一个 chattabviewmodel 时，该属性将正确绑定。所以它只在 mainwindowviewmodel 的“chattabviewmodel”集合的第一个实例和最后一个实例上触发。
经过一周的搜索，我现在有点绝望了……
到目前为止，我的假设是：问题可能与我在字典资源中将视图设置为视图模型的方式有关。视图可能是共享的，并且只有第一个滚动条可能会做出反应。我试图在 DataTemplate 标记上添加一个x:Shared = false 属性，但它没有改变任何东西。
【问题讨论】：
标签： c# wpf mvvm dependency-properties attached-properties