Question

private void button_Click(object sender, RoutedEventArgs e)
{
   var button = (Button) sender;

   var stackPanel = button.Parent as StackPanel;
   var childStackPanel = stackPanel.Children.Where(a => a is StackPanel).FirstOrDefault();

   // var textbox = childStackPanel.Children.Where(a => a is StackPanel).FirstOrDefault();
}

Not able to get Element within Element, textbox in this case.

But it gives an error when I code chidStackPanel.Children. No Children Property available.

Answer 1

Your Where is filtering out Children, which is a collection of UIElement, which does not have a Children property. You need to cast it to a StackPanel too. But rather than that, OfType to the rescue:

var childStackPanel = stackPanel.Children.OfType<StackPanel>().FirstOrDefault();

OfType filters out items that are not of that type, while also casting them to that type.