Winform中如何跨线程访问UI元素

public Form2()
{
  InitializeComponent();
  //禁止对跨线程访问做检查 (不推荐使用这种方法)
  Control.CheckForIllegalCrossThreadCalls = false;
}

//使用委托方法 将其委托给UI控件更新
private void button1_Click(object sender, EventArgs e)
{
  Thread thread1 = new Thread(new ParameterizedThreadStart(UpdateLabel2));
  thread1.Start("更新Label");
}

private void UpdateLabel2(object str)
{
  if (label2.InvokeRequired)
  {
    // 当一个控件的InvokeRequired属性值为真时，说明有一个创建它以外的线程想访问它
    Action<string> actionDelegate = (x) => { this.label2.Text = x.ToString(); };
    // 或者
    // Action<string> actionDelegate = delegate(string txt) { this.label2.Text = txt; };
    this.label2.Invoke(actionDelegate, str);
  }
  else
  {
    this.label2.Text = str.ToString();
  }
}

private SynchronizationContext synchronizationContext;
 
private void button2_Click(object sender, EventArgs e)
{
  synchronizationContext = SynchronizationContext.Current;
  new Thread(() => { UpdateText("跨线程访问"); }).Start();
}
void UpdateText(string msg)
{
  synchronizationContext.Post(_ => this.label2.Text = msg, null);
}

public partial class FileManagerForm : Form
{
  FileInfo file ;
  BackgroundWorker bw;
  ServerFile server;
  public FileManagerForm(string filePath)
  {
    InitializeComponent();

    file = new FileInfo(filePath);

    long size = file.Length / 1024 / 1024;
    lblOrgSize.Text = (int)size+ "MB";
    bw = new BackgroundWorker();
    server = new ServerFile(file.Name);
  }

  private void FileManagerForm_Load(object sender, EventArgs e)
  {
    proUpFile.Minimum = 0;
    proUpFile.Maximum = 100;

    bw.WorkerReportsProgress = true;
    bw.WorkerSupportsCancellation = true;
    bw.DoWork += Bw_DoWork;
    bw.ProgressChanged += Bw_ProgressChanged;
    bw.RunWorkerCompleted += Bw_RunWorkerCompleted;
    bw.RunWorkerAsync();
  }
  private void Bw_DoWork(object sender, DoWorkEventArgs e)
  {
    using(FileStream fileRead= file.OpenRead())
    {
      long setp = file.Length / 100;
      while (file.Length > fileRead.Position)
      {
        if (bw.CancellationPending)
        {
          break;
        }

        byte[] bytes = new byte[1024];
        int count = fileRead.Read(bytes, 0, bytes.Length);

        long writeLength= server.UpFile(bytes, count);

        if(writeLength >proUpFile.Value* setp)
        {
          int size = (int)(writeLength / 1024 / 1024);
          bw.ReportProgress(proUpFile.Value + 1, size);
        }

      }
      server.Close();
    }
  }
  private void Bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
  {
    proUpFile.Value= e.ProgressPercentage> proUpFile.Maximum?proUpFile.Maximum:e.ProgressPercentage;
    lblUpLoadSize.Text = e.UserState.ToString() + "MB";
  }

  private void Bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
  {
    if (this.proUpFile.Value == this.proUpFile.Maximum)
    {
      MessageBox.Show("文件发送成功！");
    }
    else
    {
      MessageBox.Show("文件发送失败！");
    }
    this.Close();
  }

  private void btnCancel_Click(object sender, EventArgs e)
  {
     bw.CancelAsync();
  }
}