append to textbox from another thread

Question

I've a Form with many tabs and I want to write to them in the same time from many threads (UI BackGroundWorker etc.) I've written this code and it is working on main tab ( the one that is visible when app starts )

    public struct Struct_Append
    {
        public RichTextBox Screen;
        public string Message;
        public Color Color;
    }

    public void AppendAllTextAllScreen (Struct_Append append  )
    {
        RichTextBox screenToPrint = append.Screen;
        Font font = new Font("Tahoma", 8, FontStyle.Regular);
        if (screenToPrint.InvokeRequired) //&& this.Visible)
        {

            append.Message = append.Message + "\n";
            try
            {
                this.Invoke(new Action<Struct_Append>(AppendAllTextAllScreen), new object[] { 
                append });
            }
            catch(Exception ex)
            {
                //handle exception
            }
             return; 
        }
        append.Message = append.Message + "\n";

        screenToPrint.SelectionFont = font;
        screenToPrint.SelectionColor = append.Color;
        screenToPrint.AppendText(append.Message);
    }

It is working from any thread , but once I set the screen to some of the other tabs , and fire it

        Struct_Append structAppend1 = new Struct_Append();
        structAppend1.Screen = scrnSta1;
        structAppend1.Color = Color.Bisque;
        structAppend1.Message = "THIS IS A TEST";
        AppendAllTextAllScreen(structAppend1);

VisualStudio2013 just get stuck and restart it self!!!!

BUT when I run it without DEBUG it runs fine

EDIT code that I used that spawn the ERROR

this is the I used to test the appendText method above

private async void DoSomthing()
{
            Task.Run(() =>
            {
                _Append structAppend1 = new _Append();
                structAppend1.Screen = ScrnSta1; ;
                structAppend1.Color = Color.Bisque;
                structAppend1.Message = "THIS IS A TEST";
                for (int i = 0; i < 5; i++)
                {
                    AppendAllTextAllScreen(structAppend1);
                }


            });
            Task.Run(() =>
            {
                _Append structAppend = new _Append();
                structAppend.Color = Color.Aquamarine;
                structAppend.Message = "THIS IS A TEST";
                structAppend.Screen = ScrnSta2;
                for (int j = 0; j < 5; j++)
                {
                    AppendAllTextAllScreen(structAppend);
                }
            });
}

scrnsta1/2 are two seperated tabs in my Form (main UI thread), and I call this method from there(UI thread)

what am I missing here ?

Start without debugging and see the result. Maybe VS is buggy — Georgi-it, May 19 '14 at 08:10
Why are you using a mutable struct with public fields to start with? — Jon Skeet, May 19 '14 at 08:12
Were your multiple tabs all started from the same thread? (I'd hope so, but...) — Jon Skeet, May 19 '14 at 08:13
@JonSkeet this is just for this particular test , It should be written in class , yes all thread are started from the UI thread — LordTitiKaka, May 19 '14 at 08:16
@Georgi-it I've tried it and sadly you'r right , what can I do to fix it ? re-install VS ? — LordTitiKaka, May 19 '14 at 11:41
Try with a different version, 2013 or 2012. If both don't work probably you are doing something wrong. — Georgi-it, May 20 '14 at 07:13
@Georgi-it I would like to add my code that spawn the error for you to look at , because I dont have the permission to add another VS in that time — LordTitiKaka, May 20 '14 at 10:58
I would recommend to continue the tasks on the UI thread without using invoke. It is much safer. http://stackoverflow.com/questions/4331262/task-continuation-on-ui-thread — Georgi-it, May 20 '14 at 11:11

score 1 · Accepted Answer · answered May 20 '14 at 11:12

1

To my understanding, access to Windows Forms controls from a different thread must be done by means of the Invoke method of Control, which needs the definition of suitable delegates. In your example, these delegates would be basically the lambda expressions used in the implementation of DoSometing.

answered May 20 '14 at 11:12

Codor

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I'm sorry but I dont understand where are you getting with it(maybe the problem is in me ).. Please look above , You'll see my implementation as you mentioned – LordTitiKaka May 20 '14 at 11:25
You already seem to use the `Invoke` method, however you do not check whether the call to `Invoke` is actually necessary. The Property `InvokeRequired` of Control, documented here http://msdn.microsoft.com/en-us/library/system.windows.forms.control.invokerequired.aspx can be used to decide whether `Invoke` should be used from the current thread or not. – Codor May 20 '14 at 12:14
I actually use the property as you mentioned "if (screenToPrint.InvokeRequired)" or you mean some other kind of implementation ? – LordTitiKaka May 20 '14 at 12:32
codor you are RIGHT it was my mistake – LordTitiKaka May 20 '14 at 13:16

score 1 · Answer 2 · edited May 23 '17 at 10:32

1

I would recommend to continue the tasks on the UI thread without using invoke. It is much safer and less error prone: Task continuation on UI thread

Task UITask= task.ContinueWith(() =>
{
 this.TextBlock1.Text = "Complete"; 
}, TaskScheduler.FromCurrentSynchronizationContext());

edited May 23 '17 at 10:32

Community

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1

answered May 20 '14 at 11:30

Georgi-it

3,676
1
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I get this error Error 8 Delegate'System.Action' does not take 0 arguments what should I put inside the lambda expression ? – LordTitiKaka May 20 '14 at 12:41

append to textbox from another thread

2 Answers2