Why does Crossthreading work this way?
c#, multithreading, winforms
Solution
I think it's just a timing issue. If you try to update a gui element from a non-gui thread the cross-thread exception can be thrown. You can even disable the whole cross-thread exceptions by calling
Form.CheckForIllegalCrossThreadCalls = false;
but after the exception is gone, the further behavior is undefined and can lead to very subtle bugs. So take the exception as a hint for a code smell but be aware that sometimes the exception won't be thrown even if it should be.
Problem
Solved Seems that Oliver is right. After Several tries I got the exception and in debug mode i get it for sure. So this has to be all about timing. You should also check Matthew wattsons answer ;) Example First of all a little example that shall explain my confusion. ``` using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Threading; namespace testCrossThreading { public partial class Form1 : Form { public Form1() { InitializeComponent(); new Thread(ThreadJob).Start(); } void ThreadJob() { //label1.Text = "1"; changeText(label1, "1"); } void changeText(Label L, String message) { L.Text = message; } } } ``` Question So now my question: if I uncomment `label1.Text = "1";` in the function "ThreadJob" then I get an Cross thread exception as expected. But if i leave it commented like the example shows it does work. But why? The function is called by the sub thread and I don't invoke anything. So it is still the sub Thread and not the GUI thread that changes the text of label imo. Or am I missing something? I would write it like this. ``` void ThreadJob() { Action a = () => label1.Text = "1"; this.Invoke(a); } ```