c# - 如何取消 WPF TabControl 中的选项卡更改

Question

我在 SO 上发现了多个关于这个问题的问题，但是我仍然无法找到一个可靠的解决方案。这是我在阅读答案后得出的结论。

Xaml:

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="300" Width="300" x:Name="this">
    <TabControl IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding Tabs, ElementName=this}" x:Name="TabControl"/>
</Window>

代码隐藏:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        var tabs = new ObservableCollection<string> {"Tab1", "Tab2", "Tab3"};
        Tabs = CollectionViewSource.GetDefaultView(tabs);
        Tabs.CurrentChanging += OnCurrentChanging;
        Tabs.CurrentChanged += OnCurrentChanged;
        Tabs.MoveCurrentToFirst();
        CurrentTab = tabs.First();
    }

    private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
    {
        //only show message box when tab is changed by user input
        if (!_cancelTabChange)
        {
            if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
            {
                _cancelTabChange = true;
                return;
            }
        }
        _cancelTabChange = false;
    }

    private void OnCurrentChanged(object sender, EventArgs e)
    {
        if (!_cancelTabChange)
        {
            //Update current tab property, if user did not cancel transition
            CurrentTab = (string)Tabs.CurrentItem;
        }
        else
        {
            //navigate back to current tab otherwise
            Dispatcher.BeginInvoke(new Action(() => Tabs.MoveCurrentTo(CurrentTab)));
        }
    }

    public string CurrentTab { get; set; }

    public static readonly DependencyProperty TabsProperty = DependencyProperty.Register("Tabs", typeof(ICollectionView), typeof(MainWindow), new FrameworkPropertyMetadata(default(ICollectionView)));
    public ICollectionView Tabs
    {
        get { return (ICollectionView)GetValue(TabsProperty); }
        set { SetValue(TabsProperty, value); }
    }

    private bool _cancelTabChange;
}

基本上我想显示一条确认消息，当用户导航到不同的选项卡时，如果他单击“否”- 中止转换。但是这段代码不起作用。如果多次单击“Tab2”，每次都在消息框中选择“否”，它会在某个时候停止工作:事件停止触发。如果您单击“Tab3”，事件将再次触发，但如果您选择"is"，它将打开第二个选项卡而不是第三个选项卡。我无法弄清楚 wtf 是怎么回事。 :)

有人看到我的解决方案中有错误吗？或者有没有更简单的方法来显示确认消息，当用户切换选项卡？我也愿意使用任何具有适当 SelectionChanging 事件的开源选项卡控件。但是我找不到。

我正在使用 .Net 4.0。

编辑: 如果我将消息框注释掉:

private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
{
    //only show message box when tab is changed by user input
    if (!_cancelTabChange)
    {
        //if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
        //{
            Debug.WriteLine("Canceled");
            _cancelTabChange = true;
            return;
        //}
    }
    _cancelTabChange = false;
}

一切正常。很奇怪。

Answer 1

此解决方案 http://coderelief.net/2011/11/07/fixing-issynchronizedwithcurrentitem-and-icollectionview-cancel-bug-with-an-attached-property/

似乎与

配合得很好

<TabControl ... yournamespace:SelectorAttachedProperties.IsSynchronizedWithCurrentItemFixEnabled="True" .../>

private void OnCurrentChanging(object sender, CurrentChangingEventArgs e)
{                   
    if (MessageBox.Show("Change tab?", "Message", MessageBoxButton.YesNo) == MessageBoxResult.No)
    {
        e.Cancel = true;                    
    }                     
}



public static class SelectorAttachedProperties
{
    private static Type _ownerType = typeof(SelectorAttachedProperties);

    #region IsSynchronizedWithCurrentItemFixEnabled

    public static readonly DependencyProperty IsSynchronizedWithCurrentItemFixEnabledProperty =
        DependencyProperty.RegisterAttached("IsSynchronizedWithCurrentItemFixEnabled", typeof(bool), _ownerType,
        new PropertyMetadata(false, OnIsSynchronizedWithCurrentItemFixEnabledChanged));

    public static bool GetIsSynchronizedWithCurrentItemFixEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsSynchronizedWithCurrentItemFixEnabledProperty);
    }

    public static void SetIsSynchronizedWithCurrentItemFixEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsSynchronizedWithCurrentItemFixEnabledProperty, value);
    }

    private static void OnIsSynchronizedWithCurrentItemFixEnabledChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Selector selector = d as Selector;
        if (selector == null || !(e.OldValue is bool && e.NewValue is bool) || e.OldValue == e.NewValue)
            return;

        bool enforceCurrentItemSync = (bool)e.NewValue;
        ICollectionView collectionView = null;

        EventHandler itemsSourceChangedHandler = null;
        itemsSourceChangedHandler = delegate
        {
            collectionView = selector.ItemsSource as ICollectionView;
            if (collectionView == null)
                collectionView = CollectionViewSource.GetDefaultView(selector);
        };

        SelectionChangedEventHandler selectionChangedHanlder = null;
        selectionChangedHanlder = delegate
        {
            if (collectionView == null)
                return;

            if (selector.IsSynchronizedWithCurrentItem == true && selector.SelectedItem != collectionView.CurrentItem)
            {
                selector.IsSynchronizedWithCurrentItem = false;
                selector.SelectedItem = collectionView.CurrentItem;
                selector.IsSynchronizedWithCurrentItem = true;
            }
        };

        if (enforceCurrentItemSync)
        {
            TypeDescriptor.GetProperties(selector)["ItemsSource"].AddValueChanged(selector, itemsSourceChangedHandler);
            selector.SelectionChanged += selectionChangedHanlder;
        }
        else
        {
            TypeDescriptor.GetProperties(selector)["ItemsSource"].RemoveValueChanged(selector, itemsSourceChangedHandler);
            selector.SelectionChanged -= selectionChangedHanlder;
        }
    }

    #endregion IsSynchronizedWithCurrentItemFixEnabled
}