CODEWITHSUNDEEP
c#textbox
lolalola
lolalola

Reputation: 3823

TextBox and Thread

Why doesn't this work?

The program stops on: this.textBox1.Text = "(New text)";

 Thread demoThread;
 private void Form1_Load(object sender, EventArgs e)
 {
     this.demoThread = new Thread(new ThreadStart(this.ThreadProcUnsafe));
     this.demoThread.Start();

     textBox1.Text = "Written by the main thread.";
 }

 private void ThreadProcUnsafe()
 {
     while (true)
     {
         Thread.Sleep(2000);
         this.textBox1.Text = "(New text)";           
     }
 }

Upvotes: 3

Views: 2143

Answers (4)

fre0n
fre0n

Reputation: 1915

Although I recommend using Invoke or BeginInvoke (after calling InvokeRequired of course), you can prevent the cross-thread exception altogether by calling this from your Form or UserControl:

CheckForIllegalCrossThreadCalls = false;

(CheckForIllegalCrossThreadCalls is a static property of Control)

If you choose to do this, you may get some weird-looking results in your UI.

Upvotes: 2

Paul Sasik
Paul Sasik

Reputation: 81449

Cross-thread access to Windows controls is not allowed. You need another, less direct mechanism such as event or message passing.

Here's an article on the Control.Invoke issue and why BeginInvoke is a better choice due to less chance of deadlock.

Upvotes: 2

Aaronaught
Aaronaught

Reputation: 122624

You need to use Control.Invoke when performing these operations from a background thread:

private void ThreadProcUnsafe()
{
    while (true)
    {
        Thread.Sleep(2000);
        textBox1.Invoke(new Action(() =>
        {
            textBox1.Text = "(New Text)";
        }));
    }
}

If you are writing generic code that may be run from a background thread, you can also check the Control.InvokeRequired property, as in:

if (textBox1.InvokeRequired)
{
    textBox1.Invoke(...);
}
else
{
    // Original code here
}

Upvotes: 5

Justin Ethier
Justin Ethier

Reputation: 134157

In windows, a control may only be updated by the thread that created it. You need to use Control.Invoke to marshall a method call to the UI thread to update the text.

There is an example of this on the MSDN Control.Invoke page.

Upvotes: 5

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