在 TabControl 中切换 Tab 时，TextBox 绑定不起作用

Question

I have a TextBox in a TabControl. If I edit the text in the box and then switch to another tab, the text is lost. If I change focus (via TAB key on keyboard) and then switch to another tab, the new text is set in my viewmodel.

Here is my code:

<Window x:Class="TabSwitchProblem.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<TabControl ItemsSource="{Binding Pages}">
    <TabControl.ContentTemplate>
        <DataTemplate>
            <TextBox Text="{Binding PageContent}" />
        </DataTemplate>
    </TabControl.ContentTemplate>
</TabControl>

public partial class MainWindow : Window
{
    public ObservableCollection<PageViewModel> Pages
    {
        get { return (ObservableCollection<PageViewModel>)GetValue(PagesProperty); }
        set { SetValue(PagesProperty, value); }
    }
    public static readonly DependencyProperty PagesProperty =
        DependencyProperty.Register("Pages", typeof(ObservableCollection<PageViewModel>), typeof(MainWindow), new PropertyMetadata(null));

    public MainWindow()
    {
        InitializeComponent();
        Pages = new ObservableCollection<PageViewModel>();
        Pages.Add(new PageViewModel());
        Pages.Add(new PageViewModel());
        DataContext = this;
    }
}
public class PageViewModel : DependencyObject
{
    public string PageContent
    {
        get { return (string)GetValue(PageContentProperty); }
        set { SetValue(PageContentProperty, value); }
    }
    public static readonly DependencyProperty PageContentProperty =
        DependencyProperty.Register("PageContent", typeof(string), typeof(PageViewModel), new PropertyMetadata(null));
}

How can I be sure to get the text updated in my viewmodel?

Answer 1

You may need to add UpdateSourceTrigger=LostFocus to the <TextBox Text="{Binding PageContent}" /> line.

Code should look like this

<TextBox Text="{Binding PageContent, UpdateSourceTrigger=LostFocus}" />

That should work.

Answer 2

You should set the UpdateSourceTrigger to PropertyChanged if you want your binding to update the target every time the value changes. By default the UpdateSourceTrigger for Text property of a TextBox is LostFocus , which updates the target only after the focus is lost.

<TextBox Text="{Binding PageContent, UpdateSourceTrigger=PropertyChanged}" />

Answer 3

The previously accepted answer , although it works, involves changing the binding behavior of the textbox to UpdatesourceTrigger=PropertyChanged . This may not be acceptable for some usages of textbox or other input-accepting controls.

A simple fix for this is to manually set focus to another element on your control (or the tabcontrol itself) in code-behind on SelectionChanged of your TabControl. That way the currently focused input element actually loses focus, triggering the binding:

<TabControl x:Name="MyTabControl" SelectionChanged="MyTabControl_OnSelectionChanged">

private void MyTabControl_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    MyTabControl.Focus();
}