Determine at run time if a control allows other controls to be added to it at design time

Question

I need to manipulate all controls on a form. I'm fine with accessing the Controls collection to do this. The problem comes with trying to include any controls contained within container controls such of GroupBox or Panel. I could recursively iterate the each Control's own Controls collection but this then accesses all constituent controls for non-design time containers.

Since my non-container controls all manage their constituent controls' state based on the their own properties I don't to start messing with constituent controls.

How can I determine if a control is a design time container so that I can avoid process those that are not?

I've tried checking for the Designer attribute but this returns null for both the ComboBox and the GroupBox:

foreach(Attribute attr in typeof(ctl).GetCustomAttributes(typeof(Attribute), false))
{
    if(typeof(DesignerAttribute).IsAssignableFrom(attr.GetType()))
{
    DesignerAttribute da = (DesignerAttribute)attr;
    }
}

ctl is of type Control and in my testing is either Combox or GroupBox.

In both cases the GetCustomAttributes returns an array of 1 attribute which is the toolbox icon.

I've also tried checking assignability from to the ContainerControl class but they both are because, I assume, they will both contain controls at run time.

How do I detect a design time container?

Answer 1

In case Hans doesn't come back, and anyone is interested, this is my solution to the problem based on Hans Passant's suggestion:

    public static bool IsContainerControl(this Control ctl)
    {
        if (ctl == null)
            return false;

        MethodInfo GetStyle = ctl.GetType().GetMethod("GetStyle", BindingFlags.NonPublic | BindingFlags.Instance);
        if (GetStyle == null)
            return false;

        return (bool)GetStyle.Invoke(ctl, new object[] { ControlStyles.ContainerControl });
    }