如何修复异常跨线程操作在计时器tick事件中无效？

Question

在backgroundworker dowork事件中，我正在启动计时器：

private bool cancelop = false;
        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker bgw = (BackgroundWorker)sender;
            int Counter = 0;
            int percentage = 0;
            int total = allfiles.Count;
            for (int i = 0; i < allfiles.Count; i++)
            {
                if (bgw.CancellationPending == true)
                {
                    pictureBox1.Image.Dispose();
                    pictureBox1.Image = Properties.Resources.Weather_Michmoret;
                    e.Cancel = true;
                    makeGif = false;
                    cancelop = true;
                    timer1.Stop();
                    break;
                }
                else
                {
                    timer1.Start();
                    Counter += 1;
                    percentage = Counter * 100 / total;
                    bgw.ReportProgress(percentage);
                }
            }
            if (makeGif == true)
            {
                unfreez.MakeGIF(allfiles, outputfile + DateTime.Now, 8, true);
            }
            bgw.ReportProgress(100);
            e.Result = allfiles;
        }

然后在计时器刻度事件中：

private void timer1_Tick(object sender, EventArgs e)
        {
            try
            {
                if (cancelop == true)
                {
                    // Cancel the asynchronous operation.
                    progressBar1.EndColor = Color.FromArgb(210, 0, 0);
                    label7.ForeColor = Color.Red;
                    label7.Text = "Operation Has Been Cancelled";
                    timer1.Stop();
                    backgroundWorker1.CancelAsync();
                }
                else
                {
                    this.label7.Visible = !this.label7.Visible;
                }
            }
            catch(Exception errrr)
            {
                string myer = errrr.ToString();
            }
        }

异常消息：

[System.InvalidOperationException] = {“跨线程操作无效：控制'label7'从其创建的线程以外的线程访问。”}

at System.Windows.Forms.Control.get_Handle()
   at System.Windows.Forms.Control.get_ContainsFocus()
   at System.Windows.Forms.Control.SelectNextIfFocused()
   at System.Windows.Forms.Control.SetVisibleCore(Boolean value)
   at System.Windows.Forms.Control.set_Visible(Boolean value)
   at Animated_Gifs.Form1.timer1_Tick(Object sender, EventArgs e) in d:\C-Sharp\Animated_Gifs\Animated_Gifs\Animated_Gifs\Form1.cs:line 179

第179行在计时器刻度事件中：

this.label7.Visible = !this.label7.Visible;