Text misbehaving in UITextView - ios

Question

I have a UIView subclass in which I have a UITextView. The view and the text view grow in width according to the text in the text view. When the width of the view reaches the width of the superview, the view stops growing, and the font of the text gets smaller inside the text view. Everything seems to work fine until the text starts to get smaller. The text (which is centred both horizontally and vertically) starts to lose its position and jump around after each letter I type in. Here's a visual demonstration:
https://gyazo.com/b2027ab0fa7956244842736868dbd87e.
Here are the code parts:
The delegate methods:
// After text was typed in
func textViewDidChange(textView: UITextView) {
if shouldUpdate {
updateTextFont(textView)
self.centerText()
shouldUpdate = false
}
self.centerText()
}
// Before text was typed in
func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool {
if text == "\n" {
textView.resignFirstResponder()
}
let textSize = (text as NSString).sizeWithAttributes([NSFontAttributeName: textView.font!]) // Size of only ONE letter
if frame.width+textSize.width > superview!.bounds.width {
shouldUpdate = true
}
else {
updateFrames(textSize.width)
}
//centerText()
return true
}
Font size&position methods + frame resizing method:
func updateTextFont(textView: UITextView) {
if (textView.text.isEmpty || CGSizeEqualToSize(textView.bounds.size, CGSizeZero)) {
return;
}
let textViewSize = textView.bounds.size;
let fixedWidth = textView.bounds.width;
let expectSize = textView.sizeThatFits(CGSizeMake(fixedWidth, CGFloat(MAXFLOAT)));
var expectFont = textView.font;
if (expectSize.height > textViewSize.height) {
while (textView.sizeThatFits(CGSizeMake(fixedWidth, CGFloat(MAXFLOAT))).height > textViewSize.height) {
expectFont = textView.font!.fontWithSize(textView.font!.pointSize-1)
textView.font = expectFont
}
}
else {
while (textView.sizeThatFits(CGSizeMake(fixedWidth, CGFloat(MAXFLOAT))).height < textViewSize.height) {
print(expectFont!.pointSize)
expectFont = textView.font;
textView.font = textView.font!.fontWithSize(textView.font!.pointSize+1)
}
textView.font = expectFont;
}
}
func centerText() {
self.layoutIfNeeded()
let size = self.mainTextView.sizeThatFits(CGSizeMake(CGRectGetWidth(self.mainTextView.bounds), CGFloat(MAXFLOAT)))
var topoffset = (self.mainTextView.bounds.size.height - size.height * self.mainTextView.zoomScale) / 2.0
topoffset = topoffset < 0.0 ? 0.0 : topoffset
self.mainTextView.contentOffset = CGPointMake(0, -topoffset)
}
func updateFrames(param: CGFloat) {
bounds.size.width += param
mainTextView.center = CGPoint(x: bounds.width/2, y: bounds.height/2)
centerText()
}
Please notify me if I forgot to include any part of the code.
An interesting thing I found is that if I call centerText() after a delay in textViewDidChange the text does go back to place, but by default it doesn't.
What could be the problem?
Thanks in advance!