如何取消 WPF TabControl 中的选项卡更改

Question

我在 SO 上发现了很多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>

后面的代码：

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 "no" - 中止转换。但是这段代码不起作用。如果您多次点击 "Tab2"，每次在消息框中选择 "no"，在某些时候它会停止工作：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 "yes"，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。不过我找不到。

我正在使用 .Net 4.0。

编辑： 如果我把消息框注释掉：

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。奇怪。

Answer 1

出于某种原因，添加 TabControl.Focus() 可以解决问题：

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);
            TabControl.Focus();
        }));
    }
}

我仍然不知道这里到底发生了什么。所以我很乐意接受这个答案，这对这个问题有所启发。

Answer 2

这个解决方案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
}

Answer 3

有一个更简单的解决方案。为 XAML 中的所选项目添加绑定：

    <TabControl SelectedItem="{Binding SelectedTab}" ...

然后在视图模型中：

    private Object _selectedTab;

    public Object SelectedTab
    {
        get
        {
            return _selectedTab;
        }
        set
        {
            if (_selectedTab is ADR_Scanner.ViewModel.ConfigurationViewModel && _configurationViewModel.HasChanged)
            {
                System.Windows.Forms.MessageBox.Show("Please save the configuration changes", ADR_Scanner.App.ResourceAssembly.GetName().Name, System.Windows.Forms.MessageBoxButtons.OK, System.Windows.Forms.MessageBoxIcon.Error);
            }
            else
            {
                _selectedTab = value;
            }
            OnPropertyChanged("SelectedTab");
        }
    }

显然您将 ADR_Scanner.ViewModel.ConfigurationViewModel 替换为您自己的视图模型 class。最后确保在构造函数中初始化 _selectedTab，否则 TabControl 将没有初始选择。

Answer 4

必须服从的人要求应用程序询问用户是否希望离开页面，因此这里是稍微更改的代码：

    private Object _selectedTab;

    public Object SelectedTab
    {
        get
        {
            return _selectedTab;
        }
        set
        {
            if (
                  !(_selectedTab is ADR_Scanner.ViewModel.ConfigurationViewModel) || 
                  !_configurationViewModel.HasChanged ||
                  (System.Windows.Forms.MessageBox.Show("Are you sure you want to leave this page without saving the configuration changes", ADR_Scanner.App.Current.MainWindow.Title, System.Windows.Forms.MessageBoxButtons.YesNo, System.Windows.Forms.MessageBoxIcon.Error) == System.Windows.Forms.DialogResult.Yes)
                )
            {
                _selectedTab = value;
            }
            OnPropertyChanged("SelectedTab");
        }
    }

我认为这个小改动几乎可以满足您的要求。

Answer 5

private void MainTabControl_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (ReasonBecauseLeaveTabItemIsForbidden)
        {
            if (MainTabControl.SelectedIndex == IndexOfTabItem)
            {
                MessageBox.Show(SomeMessageWhyLeaveTabItemIsForbidden);
            }
            MainTabControl.SelectedIndex = IndexOfTabItem;
        }
    }

IndexOfTabItem - 因离开而禁用的 TabItem 的索引。

Answer 6

在 tabControl_SelectionChanged 事件处理程序中：

if (e.OriginalSource == tabControl) //if this event fired from your tabControl
            {
                e.Handled = true;

                if (!forbiddenPage.IsSelected)  //User leaving the tab
                {
                    if (forbiddenTest())
                    {
                        forbiddenPage.IsSelected = true;
                        MessageBox.Show("you must not leave this page");
                    }
             }

请注意，设置 forbiddenPage.IsSelected = true 会导致循环并重新输入这个事件处理程序。然而这一次，我们退出，因为选择的页面是禁止页面。

如何取消 WPF TabControl 中的选项卡更改

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