My Timer event crashes because the events are called on a different thread.

Question

I get the error "Cross-thread operation not valid: Control 'label1' accessed from a thread other than the thread it was created on." when I run this code:

using System;
using System.ComponentModel;
using System.Data;
using System.Text;
using System.Windows.Forms;
using System.Timers;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
     System.Timers.Timer T = new System.Timers.Timer();
     public Form1()
     {
      InitializeComponent();
      T.Elapsed += new ElapsedEventHandler(T_Elapsed);
      T.Start();
     }

     void T_Elapsed(object sender, ElapsedEventArgs e)
     {
      label1.Text = "This will not work";
     }
    }
}

I thought events ran in the same thread as they were triggered in.

Answer 1

Are you remembering to use InvokeRequired? It will allow you to update a UI element on the UI thread from the Timer thread.

Answer 2

If you're doing this asynchronously (it sounds like you are), be sure that you catch exceptions in the event handler or callback. If a background thread throws an exception, it will crash the app. This is the most common cause that I've seen of this behavior.

Answer 3

I'm assuming you're talking about a WinForms application.

When trying to update a Form element (which lives on the UI thread) from another thread, you need to use Control.Invoke or Control.BeginInvoke. You pass a delegate to the method you want to invoke (or pass an anonymous method in) and then that delegate gets called on the UI thread rather than the calling thread.

Answer 4

You might be using the wrong kind of timer. Try the WinForms timer, its runs on the GUI thread so you don't have to do Invoke

Answer 5

While the "Accepted" answer is technically correct (in that this will fix the problem) this doesn't answer the question.

The ANSWER is to use

void T_Elapsed(object sender, ElapsedEventArgs e)
{
    this.BeginInvoke(new MethodInvoker(delegate(){
        label1.Text = "This will work";
    }));
}

http://jaysonknight.com/blog/archive/2007/02/14/using-anonymous-methods-for-control-invoke-control-begininvoke.aspx

Answer 6

I am not a winform developer. But i heard something regararding Timer class which you are using. I think you might want to set these properties and check.

T.Interval = 5000; //in Mili Seconds
T.Enabled = true;