BackgroundWorker - 跨线程操作无效

Question

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 1

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
}

Answer 2

try this code,

BeginInvoke((MethodInvoker)delegate
{
    richtextBox.Text.Add("MyText");
});

Answer 3

Using BackgroundWorker component, only the ProgressChanged and RunWorkerCompleted events allow you to invoke methods/properties on UI controls (which should be always done on UI thread). As you are updating the UI in DoWork event which runs on a non-UI thread you are getting this error, you should probably update you UI controls using Invoke or BeginInvoke methods in DoWork event if you want to.

Answer 4

To make it cleaner and based on Jon Skeet's suggestion, I made an extension method which does the same, you can change the " this Label control " to this TextBox control or simply use " this Control control " (and basically allow every control to be updated easily):

internal static class ExtensionMethods
{
    /// <summary>
    /// Updates the label text while being used in a multithread app.
    /// </summary>
    /// <param name="control">The control.</param>
    /// <param name="text">The text.</param>
    internal static void UpdateThreadedText(this Label control, string text)
    {
        Action action = () => control.Text = text;
        control.Invoke(action);
    }

    /// <summary>
    /// Refreshes the threaded.
    /// </summary>
    /// <param name="control">The control.</param>
    internal static void RefreshThreaded(this Label control)
    {
        Action action = control.Refresh;
        control.Invoke(action);
    }
}

And then the usage is quite simple:

this.yourLabelName.UpdateThreadedText("This is the text");
this.yourTextBoxName.UpdateThreadedText("This is the text");
this.yourControlName.UpdateThreadedText("This is the text");

or

this.yourLabelName.RefreshThreaded();

Works for me nicely :)

Answer 5

You can also try this.

this.Invoke(new MethodInvoker(delegate()
{
    richtextBox.Text.Add("MyText");
}));

Answer 6

i think the error stops on this line:

richtextBox.Text.Add("MyText");

your question i similar to this:

BackgroundWorker OnWorkCompleted throws cross-thread exception

Answer 7

Add:

e.Result = "MyText";

In your bw_DoWork And:

richTextBox1.AppendText((string)e.Result);

In your bw_RunWorkerCompleted

(Alter it to fit your code)

EDIT:

If it's done many times during the BackgroundWorker 's work, you can add:

_bw.ReportProgress(0, "MyText");

to the bw_DoWork and:

richTextBox1.AppendText((string)e.UserState);

to the bw_ProgressChanged .