How to get ListBox ItemsPanel in code behind

You can use the Loaded event for the StackPanel that is in the ItemsPanelTemplate

<Grid>    <Grid.Resources>        <Style TargetType="ListBox">            <Setter Property="ItemsPanel">                <Setter.Value>                    <ItemsPanelTemplate>                        <StackPanel x:Name="ThumbListStack" Orientation="Horizontal"                                    Loaded="StackPanel_Loaded" />                    </ItemsPanelTemplate>                </Setter.Value>            </Setter>        </Style>    </Grid.Resources>    <ListBox /></Grid>

And then in code behind

private StackPanel m_itemsPanelStackPanel;private void StackPanel_Loaded(object sender, RoutedEventArgs e){    m_itemsPanelStackPanel = sender as StackPanel;}

Another way is to traverse the Visual Tree and find the StackPanel which will be the first child of the ItemsPresenter.

public void SomeMethod(){    ItemsPresenter itemsPresenter = GetVisualChild<ItemsPresenter>(listBox);    StackPanel itemsPanelStackPanel = GetVisualChild<StackPanel>(itemsPresenter);}private static T GetVisualChild<T>(DependencyObject parent) where T : Visual{    T child = default(T);    int numVisuals = VisualTreeHelper.GetChildrenCount(parent);    for (int i = 0; i < numVisuals; i++)    {        Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);        child = v as T;        if (child == null)        {            child = GetVisualChild<T>(v);        }        if (child != null)        {            break;        }    }    return child;}

sorry I just noticed I forgot to save the edit...I realize you've already accepted an answer, but it seems more of a hack to me. Here's my implementation of FindChild, you might want to use it for the future or if you're going to be doing this often.

public static T FindChild<T>(this FrameworkElement obj, string name){    DependencyObject dep = obj as DependencyObject;    T ret = default(T);    if (dep != null)    {        int childcount = VisualTreeHelper.GetChildrenCount(dep);        for (int i = 0; i < childcount; i++)        {            DependencyObject childDep = VisualTreeHelper.GetChild(dep, i);            FrameworkElement child = childDep as FrameworkElement;            if (child.GetType() == typeof(T) && child.Name == name)            {                ret = (T)Convert.ChangeType(child, typeof(T));                break;            }            ret = child.FindChild<T>(name);            if (ret != null)                break;        }    }    return ret;}

It checks all the children and the children's children comparing the type and Name set on the control. Use it like this:

StackPanel ipanel = ThumbListBox.FindChild<StackPanel>("ThumbListStack");if(ipanel == null)    MessageBox.Show("couldn't find anything");else    MessageBox.Show("Aha! Found: " ipanel.Name);

Try out following extension method:

var childStackPanels = FindVisualChildren<StackPanel>(ThumbListBox);

Method itself:

public static IEnumerable<T> FindVisualChildren<T>(this DependencyObject depObj) where T : DependencyObject{    if (depObj != null)    {        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)        {            DependencyObject child = VisualTreeHelper.GetChild(depObj, i);            var typedChild = child as T;            if (typedChild != null)            {                yield return typedChild;            }                foreach (T childOfChild in FindVisualChildren<T>(child))            {                yield return childOfChild;            }        }    }}

PS: You can yourself extend it to check for specific control name so method would return single control instead of list.