获取错误使用Timer类时跨线程操作

Question

I have a Winform application, and I am satisfied with what it does. I want to retrieve the latest data from the database every 15 minutes and display it in a DataGridView.

I added a Timer class. Once 15 minutes has elapsed, I can call the method that retrieves and displays the data. I received error (see the screenshot attached).

What am I doing wrong here?

Below is my code:

public partial class Form1 : Form
{
    System.Timers.Timer aTimer;

    public Form1()
    {
      InitializeComponent();
      StartTimer();
    }

    private void RetrieveData()
    {

      DataTable table = new DataTable();
      table.Rows.Add(woStatus, dateReceived, dateApprovedFormatted, binNo, ppNo, woNo, daysDifference);

      dataGridViewMain.DataSource = table;
      dataGridViewMain.Sort(dataGridViewMain.Columns["Days in the shop"], ListSortDirection.Descending);
    }

    private void StartTimer()
    {
      aTimer = new System.Timers.Timer(10000); // 10secs
      aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
      RetrieveData();
      aTimer.Start();
    }

    private void OnTimedEvent(object source, ElapsedEventArgs e)
    {
      aTimer.Stop();
      aTimer.Dispose();
      StartTimer();
    }
}

Answer 1

System.Timers.Timer fires back on a random worker thread, not the UI thread. So when the code goes into RetrieveData (via OnTimedEvent then StartTimer ) it is on the wrong thread. You could use this.Invoke((MethodInvoker) delegate {...}) to get to the right thread, but it is probably simpler just to use the System.Windows.Forms.Timer component instead, since that automatically (via sync-context) fires on the UI thread.

Answer 2

I don't see any screenshot, but if your getting a cross-thread exception, I'd suspect its because you call the RetreiveData() within the StartTimer() method that's called on the timer thread when it elapses. You need to ensure that code affecting the UI is executed on the same thread as the UI, or you will get these kinds of exceptions. Take a look at the methods InvokeRequired() and Control.Invoke() that are provided to ensure method calls affecting the UI are done following a context switch back to the UI thread.