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: 
Polling the clipboard with a timer is very bad practice. The clipboard is a shared resource, and you'll be interfering with other apps that are monitoring the clipboard (via proper clipboard notification, i.e. following the rules). And you'll be colliding with whatever the user is trying to do. For example, when the user attempts to copy data to the clipboard, and you have opened it in your polling loop to examine it, he'll get "cannot open clipboard" errors or crashes. Please read up on clipboard viewers in MSDN: <http://msdn.microsoft.com/en-us/library/ff468802(v=VS.85).aspx>
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.