How to access a specific item in a Listbox with DataTemplate?

问题

I have a ListBox including an ItemTemplate with 2 StackPanels. There is a TextBox in the second StackPanel i want to access. (Change it\'s visibility to true and accept user input) The trigger should be the SelectionChangedEvent. So, if a user clicks on an ListBoxItem, the TextBlock gets invisible and the TextBox gets visible.

XAML CODE:

<ListBox Grid.Row=\"1\" Name=\"ContactListBox\" VerticalAlignment=\"Stretch\" HorizontalAlignment=\"Stretch\" ItemsSource=\"{Binding Contacts}\" Margin=\"0,36,0,0\" SelectionChanged=\"ContactListBox_SelectionChanged\">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation=\"Horizontal\" Margin=\"0,0,0,0\">
                        <toolkit:ContextMenuService.ContextMenu>
                            <toolkit:ContextMenu>
                                <toolkit:MenuItem Header=\"Edit Contact\" Click=\"ContactMenuItem_Click\"/>
                                <toolkit:MenuItem Header=\"Delete Contact\" Click=\"ContactMenuItem_Click\"/>
                            </toolkit:ContextMenu>
                        </toolkit:ContextMenuService.ContextMenu>

                        <Grid>
                            <Rectangle Fill=\"{StaticResource PhoneAccentBrush}\"
                                           Width=\"72\" Height=\"72\">
                                <Rectangle.OpacityMask>
                                    <ImageBrush ImageSource=\"/Images/defaultContactImage.png\" Stretch=\"UniformToFill\"/>
                                </Rectangle.OpacityMask>
                            </Rectangle>
                        </Grid>
                        <StackPanel>
                            <TextBox Text=\"{Binding Name}\" TextWrapping=\"Wrap\" Visibility=\"Collapsed\"/>
                            <TextBlock Text=\"{Binding Name}\" TextWrapping=\"Wrap\" Style=\"{StaticResource PhoneTextExtraLargeStyle}\" />
                            <TextBlock Text=\"{Binding Number}\" TextWrapping=\"Wrap\" Margin=\"12,-6,12,0\" Style=\"{StaticResource PhoneTextAccentStyle}\"/>
                        </StackPanel>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

I guess there are several ways to solve this, but nothing I tried worked.

My current approach looks like this

    private void ContactListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        ListBoxItem listBoxItem = ContactListBox.SelectedItem as ListBoxItem;

        DataTemplate listBoxTemplate = listBoxItem.ContentTemplate;

        // How to access the DataTemplate content?

        StackPanel outerStackPanel = listBoxTemplate.XXX as StackPanel;

        StackPanel innerStackPanel = outerStackPanel.Children[1] as StackPanel;

        TextBox nameBox = innerStackPanel.Children[0] as TextBox;
        TextBlock nameBlock = innerStackPanel.Children[1] as TextBlock;


        nameBox.Visibility = System.Windows.Visibility.Visible;
        nameBlock.Visibility = System.Windows.Visibility.Collapsed;

    }

回答1:

Thank you for your help guys!! Finally i got it. Solved the problem with the VisualTreeHelper. What a great function ^^

private void ContactListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (ContactListBox.SelectedIndex == -1)
            return;

        currentSelectedListBoxItem = this.ContactListBox.ItemContainerGenerator.ContainerFromIndex(ContactListBox.SelectedIndex) as ListBoxItem;

        if (currentSelectedListBoxItem == null)
            return;

        // Iterate whole listbox tree and search for this items
        TextBox nameBox = helperClass.FindDescendant<TextBox>(currentSelectedListBoxItem);
        TextBlock nameBlock = helperClass.FindDescendant<TextBlock>(currentSelectedListBoxItem);

helperFunction

public T FindDescendant<T>(DependencyObject obj) where T : DependencyObject
    {
        // Check if this object is the specified type
        if (obj is T)
            return obj as T;

        // Check for children
        int childrenCount = VisualTreeHelper.GetChildrenCount(obj);
        if (childrenCount < 1)
            return null;

        // First check all the children
        for (int i = 0; i < childrenCount; i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(obj, i);
            if (child is T)
                return child as T;
        }

        // Then check the childrens children
        for (int i = 0; i < childrenCount; i++)
        {
            DependencyObject child = FindDescendant<T>(VisualTreeHelper.GetChild(obj, i));
            if (child != null && child is T)
                return child as T;
        }

        return null;
    }

回答2:

With this edited function you can also search for control by name (its converted from VB.NET):

public T FindDescendantByName<T>(DependencyObject obj, string objname) where T : DependencyObject
{
    string controlneve = "";

    Type tyype = obj.GetType();
    if (tyype.GetProperty("Name") != null) {
        PropertyInfo prop = tyype.GetProperty("Name");
        controlneve = prop.GetValue((object)obj, null);
    } else {
        return null;
    }

    if (obj is T && objname.ToString().ToLower() == controlneve.ToString().ToLower()) {
        return obj as T;
    }

    // Check for children
    int childrenCount = VisualTreeHelper.GetChildrenCount(obj);
    if (childrenCount < 1)
        return null;

    // First check all the children
    for (int i = 0; i <= childrenCount - 1; i++) {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);
        if (child is T && objname.ToString().ToLower() == controlneve.ToString().ToLower()) {
            return child as T;
        }
    }

    // Then check the childrens children
    for (int i = 0; i <= childrenCount - 1; i++) {
        string checkobjname = objname;
        DependencyObject child = FindDescendantByName<T>(VisualTreeHelper.GetChild(obj, i), objname);
        if (child != null && child is T && objname.ToString().ToLower() == checkobjname.ToString().ToLower()) {
            return child as T;
        }
    }

    return null;
}

回答3:

I can't give you a complete answer...

But I think you can use the VisualTreeHelper to iterate through the children of any control http://blogs.msdn.com/b/kmahone/archive/2009/03/29/visualtreehelper.aspx

However, for the effect you are looking for, then I think using the SelectedItem Style might be a better solution - e.g. see this article - http://joshsmithonwpf.wordpress.com/2007/07/30/customizing-the-selected-item-in-a-listbox/

回答4:

Since DataTemplate is a generic template that could be used many times in the code, there is no way to access it by name (x:Name="numberTextBox").

I solved similar problem to this by making a collection of Controls - while Listbox was populating I add Textbox control to the collection.

string text = myCollectionOfTextBoxes[listbox.SelectedIndex].Text; 

Till I found a better soultion - Tag property. In your ListboxItem you bind Tag property to the name

Tag="{Binding Name}"

and the to access it

ListBoxItem listBoxItem = ContactListBox.SelectedItem as ListBoxItem;

string name = listBoxItem.Tag.ToString(); 

回答5:

Use ItemContainerGenerator.

private void ContactListBox_SelectionChanged
  (object sender, SelectionChangedEventArgs e)
{
  if (e.AddedItems.Count == 1)
  {
    var container = (FrameworkElement)ContactListBox.ItemContainerGenerator.
                      ContainerFromItem(e.AddedItems[0]);

    StackPanel sp = container.FindVisualChild<StackPanel>();
    TextBox tbName = (TextBox) sp.FindName("tbName");
    TextBlock lblName = (TextBlock)sp.FindName("lblName");
    TextBlock lblNumber = (TextBlock)sp.FindName("lblNumber");
  }
}

来源：https://stackoverflow.com/questions/5181063/how-to-access-a-specific-item-in-a-listbox-with-datatemplate