程间操作无效: 从不是创建控件的线程访问它。

访问 Windows 窗体控件本质上不是线程安全的。 如果有两个或多个线程操作某一控件的状态，则可能会迫使该控件进入一种不一致的状态。 还可能会出现其他与线程相关的 Bug，例如争用情况和死锁。 确保以线程安全方式访问控件非常重要。

// This method demonstrates a pattern for making thread-safe
        // calls on a Windows Forms control. 
        //
        // If the calling thread is different from the thread that
        // created the TextBox control, this method creates a
        // SetTextCallback and calls itself asynchronously using the
        // Invoke method.
        //
        // If the calling thread is the same as the thread that created
        // the TextBox control, the Text property is set directly. 

        private void SetText(string text)
        {
            // InvokeRequired required compares the thread ID of the
            // calling thread to the thread ID of the creating thread.
            // If these threads are different, it returns true.
            if (this.textBox1.InvokeRequired)
            {    
                SetTextCallback d = new SetTextCallback(SetText);
                this.Invoke(d, new object[] { text });
            }
            else
            {
                this.textBox1.Text = text;
            }
        }

详情请参考微软MSDN：https://msdn.microsoft.com/query/dev10.query?appId=Dev10IDEF1&l=ZH-CN&k=k(EHINVALIDOPERATION.WINFORMS.ILLEGALCROSSTHREADCALL);k(TargetFrameworkMoniker-".NETFRAMEWORK%2cVERSION%3dV4.0");k(DevLang-CSHARP)&rd=true