线程间操作无效: 从不是创建控件的线程访问它的三种方法

delegate void SetTextCallBack(string text);
        private void SetText(string text)
        {
            if (this.txt_a.InvokeRequired)
            {
                SetTextCallBack stcb = new SetTextCallBack(SetText);
                this.Invoke(stcb , new object[] { text});
            }
            else
            {
                this.txt_a.Text = text;
            }
        }
 
        private void LoadData()
        {
            SetText("测试");
        }
 
 
        //窗体加载时，用线程加载数据
        private void Frm_ImportManager_Load(object sender, EventArgs e)
        {
            ThreadStart ts = new ThreadStart(LoadData);
            Thread thread = new Thread(ts);
            thread.Name = "LoadData";
            thread.Start();
        }

// This event handler starts the form‘s 
        // BackgroundWorker by calling RunWorkerAsync.
        //
        // The Text property of the TextBox control is set
        // when the BackgroundWorker raises the RunWorkerCompleted
        // event.
        private void setTextBackgroundWorkerBtn_Click(
            object sender, 
            EventArgs e)
        {
            this.backgroundWorker1.RunWorkerAsync();
        }
        
        // This event handler sets the Text property of the TextBox
        // control. It is called on the thread that created the 
        // TextBox control, so the call is thread-safe.
        //
        // BackgroundWorker is the preferred way to perform asynchronous
        // operations.

        private void backgroundWorker1_RunWorkerCompleted(
            object sender, 
            RunWorkerCompletedEventArgs e)
        {
            this.textBox1.Text = 
                "This text was set safely by BackgroundWorker.";
        }