[英]why WPF Window.Visibility binding must have Mode=TwoWay for property's get to be called?
[英]why binding CollectionView to Window.Visibility does not work while binding to same bound property works for ItemsControl?
下面的ItemsControl綁定起作用,並且刷新collectionview時,控件中的工具欄也會相應刷新。 但是,可見性綁定不起作用(甚至一次),並且永遠不會調用該轉換器。 輸出窗口中沒有錯誤。
<Window.Resources>
<xpui:IEnumerableHasItemsToVisibilityConverter x:Key="IEnumerableHasItemsToVisibilityConverter" />
<ContextMenu x:Key="ToolbarContextMenu">
<MenuItem Header="Move to top" Click="MoveToTopClick" />
<MenuItem Header="Move to left" Click="MoveToLeftClick"/>
</ContextMenu>
<xpui:MenuItemToToolbarConverter x:Key="menutotoolbarconverter" />
</Window.Resources>
<ItemsControl Name="Toolbars" ItemsSource="{Binding GuiItemsInstance.FloatingToolbarsView}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ContentControl Content="{Binding Converter={StaticResource menutotoolbarconverter}, ConverterParameter={StaticResource ToolbarContextMenu}}"/>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
<Window.Visibility>
<Binding Path="GuiItemsInstance.FloatingToolbarsView" Converter="{StaticResource IEnumerableHasItemsToVisibilityConverter}"/>
</Window.Visibility>
在GuiItems-singleton(GuiItemsInstance是ViewModel的屬性)中,實現INotifyPropertyChanged
public CollectionView FloatingToolbarsView
{
get;
private set;
}
//I also tried to bind directly to FloatVisibility:
private Visibility _floatVisibility = Visibility.Hidden;
public Visibility FloatVisibility
{
get { return _floatVisibility; }
set
{
_floatVisibility = value;
// Sets the property value. Raises the PropertyChanged event, if needed.
SetValue(ref _floatVisibility, value);
}
}
///Event of changes in underlying toolbar collection is handled like this
private void RefreshFloatingToolbars(int RoleId)
{
ActiveRoleId = RoleId;
FloatingToolbarsView.Refresh();
if (ToolbarItems.Any(i => i.ToolbarLocation == ToolbarLocation.Float && i.RoleId == RoleId))
FloatVisibility = Visibility.Visible;
else
FloatVisibility = Visibility.Hidden;
}
轉換器:
public class IEnumerableHasItemsToVisibilityConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
if (value != null)
{
if (((IEnumerable)value).GetEnumerator().MoveNext())
return Visibility.Visible;
}
return Visibility.Hidden;
}
ViewModel:
//WindowViewModel implements INotifyPropertyChanged
public class FloatingToolbarWindowViewModel : WindowViewModel
{
public GuiItems GuiItemsInstance { get; set; }
public FloatingToolbarWindowViewModel(GuiItems guiItems)
{
GuiItemsInstance = guiItems;
GuiItemsInstance.Host = Host;
}
}
這根本不起作用,也嘗試像這樣綁定到ItemsControl本身:
<Window.Visibility>
<Binding Path="ItemsSource" ElementName="Toolbars" Converter="{StaticResource IEnumerableHasItemsToVisibilityConverter}"/>
</Window.Visibility>
這導致調用轉換器的值為null。
發生這種情況是因為CollectionView
實現了ICollectionChanged
,當集合中的項目發生更改時會觸發該事件。 ItemsControl
查找此事件並做出適當的反應。 一個“普通”控件偵聽CollectionView
確實實現的IPropertyChanged
通知,但不會觸發對基礎集合的更改。 因此,永遠不會將更改通知您的綁定。
您可以“鈎住” CollectionChanged
事件,並通過綁定發送適當的PropertyChanged
事件,但是此時,自己更改可見屬性可能更容易。
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