Question: I'm trying to detect every time the clipboard data changes. And so, I set a timer and have it continuously check `Clipboard.GetText()` for changes.

I'm using the following code:

```
public void WaitForNewClipboardData()
{
    //This is in WPF, Timer comes from System.Timers
    Timer timer = new Timer(100);
    timer.Elapsed += new ElapsedEventHandler(
        delegate(object a, ElapsedEventArgs b){
            if (Clipboard.GetText() != ClipBoardData)
            {
                SelectedText.Text = Clipboard.GetText();
                ClipBoardData = Clipboard.GetText();
                timer.Stop();
            }
        });
    timer.Start();
}

```

I get the following error when it runs:

> 
> Current thread must be set to singlethread apartment (STA) mode before OLE calls can be made.
> 
> 
> 

Does anyone know why?

Answer: 
Your method accesses the Clipboard class, which is an OLE call that needs the caller to be in STA mode. Most likely the issue here is with your timer, which operates on a different thread. Here is a link that will help you out with more information about this:

<http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/2411f889-8e30-4a6d-9e28-8a46e66c0fdb/>

Also, here is a link to a full article on how to monitor the clipboard by tapping into the Windows events:

<http://www.radsoftware.com.au/articles/clipboardmonitor.aspx>

I think this article will give you some tips on how better to monitor the clipboard and thus you will avoid this issue. While it is still good to know why the error occurred, there is a better way for this task to be accomplished.
Not entirely sure with this but have you tried invoking the changing of text? I had the exact same error (although in a very different scenario) and invoking a method to change a control property solved it.

I created a delegate with a string parameter:

```
public delegate void TextBoxChangeDelegate(string text);

```

Then a method that will do the actual changing:

```
void TextBoxChange(string text)
{
   MyTextBox.Text = text;
}

```

Then I invoke this method in my thread process (and in your case, the timer event):

```
public void ThreadService()
{
  while(Running)
  {
    Invoke(new TextBoxChangeDelegate(TextBoxChange), new object[] { "New Value: "+ strNewValue });
  }

}

```

This was in WinForms. It was back when I knew for the first time that changing control properties on a thread other than the UI thread causes problems. Sorry if this isn't even close to what you're trying.