C# 线程弹出子窗体 采用委托弹出模态框，使不能操作主窗体

    private void ThreadLockApp()
        {
            Thread th = new Thread(new ThreadStart(ThreadLockAppEx));
            th.IsBackground = true;
            th.Start();
        }
        
        public delegate void deleLockApp();

        private void ThreadLockAppEx()
        {
            deleLockApp dele = new deleLockApp(LockApp);
            this.Invoke(dele);
        }

        private void LockApp()
        {
            Form3 formAppExit = new Form3();
            formAppExit.ShowDialog();
        }