thread problem in textbox control access!

Question

Hye everybody!

I've got a problem with a textbox access. I'm using VS2008, WPF, c#.
I've got two projects in a solution. In one project i update an xml doc. In the other project, in wich my textbox is declared, i have declared a FileSystemWatcher who detect when my xml doc change. When it changes i whant to put a text in my textbox. Unfortunatly it raise a InvalidOperationExeption and write: "The calling thread cannot access this object because a different thread owns it.". I don't know how to solve this problem. Is anyone can help?

yohann · Answer

Thank you for your answer. You're right the best way to solve my problem is to use delegate. I tried it and it's work well now. again thanks.

Ryan Alford · Answer

here is a sample application that uses 2 threads(the main UI thread and another thread to loop through numbers). It updates a textbox from the second thread(non-UI thread) using a delegate. namespace ThreadingUIUpdate { public partial class Form1 : Form { public delegate void UpdateTextCallback(string message); public Form1() { InitializeComponent(); } private void btnStart_Click(object sender EventArgs e) { Thread thread = new Thread(new ThreadStart(TestThread)); thread.Start(); } private void UpdateText(string message) { textBox1.Text = message; } private void TestThread() { for (int i = 0; i { Thread.Sleep(1000); textBox1.Invoke(new UpdateTextCallback(this.UpdateText) new object[] { i.ToString() }); } } } } This is what you need to do. You are trying to do a cross-thread action which isn't allowed. The Invoke method will fire the delegate on the thread that owns the control.

Nilanka Dharmadasa · Answer

Yohann The 'TextBoxHandler' code should be there inside the class where the text box is created. Did you try that way?

yohann · Answer

Nilanka I tried your solution of delegate but it seems to doesn't work. The same problem raises (The calling thread cannot access this object because a different thread owns it.). I don't know wich thread can own the textbox! ...

yohann · Answer

thank you nilanka for your answer the probleme is that i can't acces my textbox via the textboxhandler class. All the controls in my window application aren't public. So How can I access them from the outside?

Nilanka Dharmadasa · Answer

According to what i understood the text box is owned by one thread while the file system watcher is runing on another thread. You may use a delegate to solve this issue. public partial class TextBoxHandler { public delegate void DelegateUpdateText( String s); public DelegateUpdateText _DelegateUpdateText ; public TextBoxHandler() { _DelegateUpdateText = new DelegateUpdateText( this .UpdateTextMethod); } public void UpdateTextMethod( string s) { TextBox1.Text = s; } } Now in the file system watcher you can call this delegate '_DelegateUpdateText'. Not the method 'UpdateTextMethod'. TextBoxHandler _obj = new TextBoxHandler (); _obj .Invoke(_obj ._DelegateUpdateText new object [] { File change detected. }); I'm not sure that I have identified your problem exactly. Hope this one will work.