How do I join two control collections for use with foreach statement

Question

As per the question I have two panels on my form one called leftPanel and one called rightPanel. These control a two column layout on my form.

I also have collapsing/expanding groupboxes inside these panels and I wish to iterate over each one to refresh the layout causing them to snap up below each other when the sizing changes.

Here is the code I have:

    private void RefreshLayout()
    {
        int rollingTopLeft = grpiAddressDetails.Top + grpiAddressDetails.Height + 10;
        int rollingTopRight = grpiBranding.Top + grpiBranding.Height + 10;
        foreach(Control temp in leftPanel.Controls && rightPanel.Controls)
        {
            if (temp is GroupBox)
            {
                if (!(temp.Name.Contains("grpi")))    // Top group boxes have 'i' as the 4th character in their name.
                {
                    if (temp.Parent == leftPanel)
                    {
                        temp.Top = rollingTopLeft;
                        rollingTopLeft += temp.Height + 10;
                    }
                    else if(temp.Parent == rightPanel)
                    {
                        temp.Top = rollingTopRight;
                        rollingTopRight += temp.Height + 10;
                    }
                }
            }
        }
    }

This is the line where I need to join the collections:

foreach(Control temp in leftPanel.Controls && rightPanel.Controls)

I realise that && does not work, have also tried Controls.Concat but Control Collections do not seem to have this function. Hope everything is clear!

Answer 1

var allControls = leftPanel.Controls.Cast<Control>().Concat(rightPanel.Controls.Cast<Control>());
foreach(Control temp in allControls)
{
     //...
}