Kris-I Kris-I - 3 months ago 44
C# Question

BackgroundWorker - Cross-thread operation not valid

I have a winform application (one form), on this form there is a RichTextBox. In the constructor of this form I create an instance of the class

MyClass
. In the “Form_Load” I call the method
Initialisation
from
MyClass
instance.

In the form constructor

myClass = new MyClass(RichTextBox richTextBox);


In the Form_Load

myClass.Initialisation();


In the
Initialisation
method, in a loop, I read some parmeters do other stuffs. To not freeze the application (because some operation can take a while, some seconds), I use a
BackgroundWorker
. I use it like this (see code below).

When I execute, I get this error : Cross-thread operation not valid: Control ‘richTextBox’
accessed from a thread other than the thread it was created on
.

Could you tell me how solve this ? Work perfect when I don't access the
richTextBox


public Class MyClass
{
static BackgroundWorker _bw;
public MyClass()
{
_bw = new BackgroundWorker
{
WorkerReportsProgress = true,
WorkerSupportsCancellation = true
};
_bw.DoWork += bw_DoWork;
_bw.ProgressChanged += bw_ProgressChanged;
_bw.RunWorkerCompleted += bw_RunWorkerCompleted;
}
static void bw_DoWork(object sender, DoWorkEventArgs e)
{
foreach (....)
{
if (....)
{
richtextBox.Text.AppendText("MyText");
}
}
e.Result = true;
}
static void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e){}
static void bw_ProgressChanged(object sender, ProgressChangedEventArgs e){}
}

Answer

Using BackgroundWorker doesn't exempt you of the normal threading rules - such as that only the UI thread can access UI components.

If you want to update the UI from a BackgroundWorker other than using the progress/completion events (which are raised on the UI thread) you need to use Control.Invoke / Control.BeginInvoke just as you would in other situations. For example:

if (....)
{
    Action action = () => richtextBox.Text.Add("MyText");
    richtextBox.Invoke(action); // Or use BeginInvoke
}