Cross-thread operation not valid: while tried to remove item from Listbox

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Cross-thread operation not valid: Control listbox1 accessed from a thread other than the thread it was created on

I have delegate for ADD items in ListBox. Before add new item I check is it already in the list If yes then Remove from the List and add new one.

As I tried to remove old item It gives error.

"Cross-thread operation not valid: Control listbox1 accessed from a thread other than the thread it was created on"

Can't I do both operation together in single call??

Please help me!!! :(

Thank you
Seema

Posted 15-Feb-11 22:21pm

Seema Gosain

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2 solutions

Solution 2

Leave alone Google, did you even try to find answer on CP before posting the question.
I did the google search and the first result was for this [^]on Code Project.

It explains it nicely.

Posted 15-Feb-11 22:46pm

Manas Bhardwaj

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Seema Gosain 16-Feb-11 10:09am

Yes, I also tried and found but my issue is to remove the items.Forthis I Listbox1.InvokeRequired{}else{}
But I want to remove item before adding new item :(

Sergey Alexandrovich Kryukov 16-Feb-11 12:50pm

This is VB.NET (what can VB be good :-), C# requested. You're right about Google and CP, of course.
--SA

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Dylan Morley · Accepted Answer · 2011-02-15T22:46:00

You should only access UI elements from the thread that created them

How to: Make Thread-Safe Calls to Windows Forms Controls [^]

Use the 'InvokeRequired' property of your listbox to see if you need to marshal back to the UI thread

e.g.

C#

private void LoadItems()
{
    // InvokeRequired required compares the thread ID of the
    // calling thread to the thread ID of the creating thread.
    // If these threads are different, it returns true.
    if (this.listbox1.InvokeRequired)
    {
        SetTextCallback d = new SetTextCallback(SetText);
        this.Invoke(d, new object[] { text });
    }
    else
    {
        // Load your items here
    }
}

Alternatively, if you're using .Net 4.0, you might want to look at the Task Parallel Library[^] which allows you to use continuations and pass a Synchronization Context that automatically marshalls back to the UI

http://blogs.msdn.com/b/csharpfaq/archive/2010/06/18/parallel-programming-task-schedulers-and-synchronization-context.aspx[^]

Edit: Just noticed the .Net 3.5 tag! I'll leave the TPL reference in my answer though, might help someone else