I currently have the following code:

```
class NewPostController: UIViewController {

@IBOutlet weak var MessageField: UITextView!

override func viewDidLoad() {
    super.viewDidLoad()
    MessageField.text = "What's on your mind?"
    MessageField.textColor = UIColor.lightGrayColor()
}

func textViewDidBeginEditing(MessageField: UITextView) {
    if MessageField.textColor == UIColor.lightGrayColor() {
        MessageField.text = ""
        MessageField.textColor = UIColor.blackColor()
    }
}

```

However, whenever I edit `MessageField`, the code within `textViewDidBeginEditing` doesn't run. I suspect this is because of an invalid way of referencing `MessageField` within the function, but I don't know what to do.