Adding Children to nested StackPanel (System.InvalidOperationException)

Question

Im trying to add a Child to a StackPanel ("messageChain") which is inside a StackPanel ("newMessage") which is inside ANOTHER StackPanel ("Messages").

Im basically trying to make a chat with messages and profile pictures but i came up with these "message chains" because if i dont have those then every message will contain a profile picture which i dont want, i want a profile picture to only be next to the first message.

Ive read other questions about this but im still not sure if i understand... can i not add children to an existing StackPanel within an existing StackPanel within an existing StackPanel? Creating the first message works, but creating the second doesnt and gives an exception because thats where i try to add a child to the nested StackPanel.

If this isnt possible, what would be a better way to do what im trying to do?

Anyway here is the code, and under it the exception i get and a screenshot of what im trying to do, in case my explanation doesnt make sense

// New message chain
StackPanel messageChain = new StackPanel();
messageChain.Children.Add(messageTB);

// Create horizontal message StackPanel (PFP & MessageChain) for new message
StackPanel newMessage = new StackPanel();
newMessage.Name = "Local";
newMessage.Orientation = Orientation.Horizontal;

newMessage.Margin = new Thickness(0, 0, 10, 5);
newMessage.HorizontalAlignment = HorizontalAlignment.Left;

if (Messages.Children.Count <= 0)
{
    newMessage.Children.Add(pfpGrid);
    newMessage.Children.Add(messageChain);

    Messages.Children.Add(newMessage);
}
else
{
    if (Messages.Children[Messages.Children.Count - 1] is StackPanel msg)
    {
        if (msg.Name == "Local")
        {
            if (msg.Children[1] is StackPanel msgChain) // this adds the new message textblock to the previously created StackPanel "messageChain" which is inside the also previously created StackPanel "newMessage"
            {
                msgChain.Children.Add(messageTB); // EXCEPTION: CANT add new TextBlock to already existing StackPanel
            }
        }
        else
        {
            newMessage.Children.Add(pfpGrid);
            newMessage.Children.Add(messageTB); //message wont wrap here
            Messages.Children.Add(newMessage);
        }
    }
}

This is the exception i get (i commented where i get it in the code):

System.InvalidOperationException: Specified element is already the logical child of another element. Disconnect it first. at System.Windows.FrameworkElement.ChangeLogicalParent(DependencyObject newParent) at System.Windows.FrameworkElement.AddLogicalChild(Object child) at System.Windows.Controls.UIElementCollection.AddInternal(UIElement element) at System.Windows.Controls.UIElementCollection.Add(UIElement element) at Soxkets.ServerPage.Chatbox_KeyDown(Object sender, KeyEventArgs e) in C:\Users\demented\Desktop\C#Programs\Soxkets\ServerPage.xaml.cs:line 333

Here is a screenshot explaining what im trying to do, if that helps:

You are adding `messageTB` to a container in two places. Hence the error description `Specified element is already the logical child of another element. Disconnect it first`. — andrew, Aug 03 '21 at 04:56
Im adding it to a container within a container, is this not allowed? — , Aug 03 '21 at 15:50
There are multiple lines in your code where you call `x.Children.Add(messageTB)` where `messageTB` is the same control. A control can only be a direct child of one container at a time. Are you sure you want to add the same textblock, or did you mean to create a new one and add that to the new message? — andrew, Aug 04 '21 at 00:50
I'd also encourage you to use databound XAML templates to handle this sort of UI construction. It simplifies the code and avoids these sort of coding errors. — andrew, Aug 04 '21 at 00:51
OHHH so a child can only be the child of ONE parent? i didnt know that thank you — , Aug 04 '21 at 04:18
i actually used a DockPanel and i got my chat working the way i wanted, but i now have a new issue, my scrollviewer cant scroll through the content of the DockPanel (the textblocks) because the scroll viewer holds the stackpanel Messages which holds the DockPanel. so now i can only scroll through the content of the Messages stackpanel but the elements are big because theyre whole DockPanels — , Aug 04 '21 at 04:25
That would need to be a separate question. You would need to show your XAML or a diagram showing the structure of the elements (which is why XAML is nice: it's self-documenting). You could diagram your *desired* visual structure, including which area should scroll, and someone can provide help with choosing an appropriate WPF element hierarchy. Your existing picture doesn't really show us much because there is only one message and no scroll area indicated (and it contains superfluous elements). — andrew, Aug 04 '21 at 07:05
hey, i fixed the scrollviewer issue by putting the scroll bar to Hidden and disabling CanContentScroll, thanks for the explanations tho — , Aug 05 '21 at 15:43

Adding Children to nested StackPanel (System.InvalidOperationException)

0 Answers0