Silverlight TabItem 可见性没有改变

Question

我有一个 TabControl，其中有许多 TabItems 绑定到一个 ViewModel，该 ViewModel 具有每个 TabItem 的可见性的属性。

<sdk:TabControl>
    <sdk:TabItem Name="Inventory" Header="Inventory" 
        Style="{StaticResource TabItemStyle}"
        Visibility="{Binding Permissions.Inventory,
        Converter={StaticResource PermissiveVisibilityConverter}, 
            ConverterParameter='Viewer'}"
        DataContext="{Binding VM}" />

</sdk:TabControl>

所有 TabItems 默认为折叠的可见性。但是，当 VM 将 TabItem 更改为 Visible 时，它​​不会工作，直到您将鼠标移到控件上...

即使我使用按钮以编程方式设置可见性，它的行为也是一样的！

我检查了 VM 的属性是否正在通知 UI，并且它们与 NotifyOnPropertyChanged 一起使用。如果我将数据绑定到按钮的可见性，它就可以正常工作...只是 TabItems 似乎有错误。

有没有办法让 TabItem UI 刷新？或者解决这个问题？

谢谢！

Answer 1

如果您更改 xaml 以便首先设置 DataContext 会怎样：

 <sdk:TabItem Name="Inventory" Header="Inventory" 
    Style="{StaticResource TabItemStyle}"
    DataContext="{Binding VM}"
    Visibility="{Binding Permissions.Inventory,
    Converter={StaticResource PermissiveVisibilityConverter}, 
        ConverterParameter='Viewer'}" />

我假设 Permissions.Inventory 是您的视图模型上的一个属性，但由于您当时尚未设置上下文，因此绑定似乎不起作用。

另外，如果您设置断点并且调用 Permissions.Inventory 上的 getter，您的转换器是否会被命中？

Answer 2

我遇到了同样的问题，我能够使用附加的“可见性”属性而不是原始属性来克服它。在这个新属性中，我可以将值传递给原始的“Visibility”属性，如果父选项卡控件的“SelectedItem”被折叠，请选择下一个可见的 tabItem。

但是，正如here 所述，如果在加载 TabControl 时折叠第一个项目，这可能还不够。这种情况必须在 TabControl 本身中修复，因为测试显示当第一次设置假的“可见性”时，TabItem 还没有访问它的 TabControl。因此，我还使用了 TabControl 的附加属性来纠正此问题。

完整的解决方案：

public static class TabControlExtensions
{
    /// <summary>
    /// Use this property on a TabControl to correct the behavior
    /// of selecting Collapsed TabItems.
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public static bool GetSelectOnlyVisibleTabs(DependencyObject obj)
    {
        return (bool)obj.GetValue(SelectOnlyVisibleTabsProperty);
    }
    public static void SetSelectOnlyVisibleTabs(DependencyObject obj, bool value)
    {
        obj.SetValue(SelectOnlyVisibleTabsProperty, value);
    }
    public static readonly DependencyProperty SelectOnlyVisibleTabsProperty =
        DependencyProperty.RegisterAttached("SelectOnlyVisibleTabs", typeof(bool), typeof(TabControlExtensions), new PropertyMetadata(false, SelectOnlyVisibleTabsChanged));
    public static void SelectOnlyVisibleTabsChanged(object sender, DependencyPropertyChangedEventArgs args)
    {
        var tabControl = sender as TabControl;
        if (tabControl == null) return;

        if ((bool)args.NewValue)
        {
            tabControl.SelectionChanged += TabControl_SelectionChanged;
            CorrectSelection(tabControl);
        }
        else
        {
            tabControl.SelectionChanged -= TabControl_SelectionChanged;
        }
    }

    private static void TabControl_SelectionChanged(object sender, SelectionChangedEventArgs args)
    {
        var tabControl = sender as TabControl;
        if (tabControl == null) return;

        CorrectSelection(tabControl);
    }

    public static void CorrectSelection(TabControl tabControl)
    {
        var selected = tabControl.SelectedItem as UIElement;
        if (selected == null) return;

        // If the selected element is not suposed to be visible,
        // selects the next visible element
        if (selected.Visibility == System.Windows.Visibility.Collapsed)
            tabControl.SelectedItem = tabControl.Items.OfType<UIElement>()
                .Where(e => e.Visibility == System.Windows.Visibility.Visible)
                .FirstOrDefault();
    }
}

public static class TabItemExtensions
{
    /// <summary>
    /// Use this property in a TabItem instead of the original "Visibility" to 
    /// correct the behavior of a TabControl when a TabItem's Visibility changes.
    /// </summary>
    /// <param name="obj"></param>
    /// <returns></returns>
    public static Visibility GetVisibility(DependencyObject obj)
    {
        return (Visibility)obj.GetValue(VisibilityProperty);
    }
    public static void SetVisibility(DependencyObject obj, Visibility value)
    {
        obj.SetValue(VisibilityProperty, value);
    }
    public static readonly DependencyProperty VisibilityProperty =
        DependencyProperty.RegisterAttached("Visibility", typeof(Visibility), typeof(TabItemExtensions), new PropertyMetadata(Visibility.Visible, VisibilityChanged));

    public static void VisibilityChanged(object sender, DependencyPropertyChangedEventArgs args)
    {
        var tabItem = sender as TabItem;
        if (tabItem == null) return;

        var visibility = (Visibility)args.NewValue;
        if (tabItem.Visibility == visibility) return;

        tabItem.Visibility = visibility;
        if (visibility == Visibility.Visible) return;

        // Finds the tab's parent tabcontrol and corrects the selected item, 
        // if necessary.
        var tabControl = tabItem.Ancestors().OfType<TabControl>().FirstOrDefault();
        if (tabControl == null) return;

        TabControlExtensions.CorrectSelection(tabControl);
    }
}

用法：

<sdk:TabControl local:TabControlExtensions.SelectOnlyVisibleTabs="True">
        <sdk:TabItem Header="tabItem1" Visibility="Collapsed">
            <TextBlock HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       Text="TabItem1 which should not be visible (1)" />
        </sdk:TabItem>
        <sdk:TabItem Header="tabItem2">
            <TextBlock HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       Text="TabItem2 which should be visible (2)" />
        </sdk:TabItem>
        <sdk:TabItem DataContext="{Binding ViewModel}"
                     Header="tabItem3"
                     local:TabItemExtensions.Visibility="{Binding MyProperty,
                                                                 Converter={StaticResource BoolToVisibilityConverter}}">
            <TextBlock HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       Text="TabItem with binded Visibility (3)" />
        </sdk:TabItem>
    </sdk:TabControl>