iSpyApplication.MainForm.MediaSelectAll C# (CSharp) Method

        internal void MediaSelectAll()
        {
            bool check = false, first = true;
            lock (ThreadLock)
            {
                foreach (Control c in flowPreview.Controls)
                {
                    var pb = c as PreviewBox;
                    if (pb != null)
                    {
                        if (first)
                            check = !pb.Selected;
                        first = false;
                        pb.Selected = check;
                    }
                }
                flowPreview.Invalidate(true);
            }
        }