Calculate NSString size to adjust UITextField frame - ios

Question

I have issues calculating the accurate size of a NSString displayed in a UITextField.
My goal is to update the textfield frame size according to the string size programmatically (without using sizeToFit). I am using the sizeWithFont function.
-(void)resizeTextFieldAccordingToText:(NSString*)textFieldString {
CGPoint originalCenter = self.textField.center;
UIFont* currentFont = [textField font];
CGSize newSize = [textFieldString sizeWithFont:currentFont];
//Same incorrect results with the extended version of sizeWithFont, e.g.
//[textFieldString sizeWithFont:currentFont constrainedToSize:CGSizeMake(300.0, 100.0) lineBreakMode:NSLineBreakByClipping];
[self.textField setFrame:(CGRectMake(self.textField.frame.origin.x, self.textField.frame.origin.y, newSize.width, newSize.height))];
[self.textField setCenter:originalCenter];
}
Problem: While this return correct size results at first its becomes more and more unprecise by adding characters therefore finally starts clipping the string (as seen in the right screenshot).
How do I get the accurate size of the textField string for correctly adjusting its size?

Answer 1

UITextField has it's own layout inside if you use borderStyle != UITextBorderStyleNone. In this case you have to increase text size dimensions by some constants.
With UITextBorderStyleNone you don't have this problem, and code below works like a charm (iOS 7 introduced new method to get text size, -sizeWithFont: is deprecated)
- (IBAction)textChanged:(UITextField *)field
{
UIFont *font = field.font;
NSString *string = field.text;
CGSize size = [string sizeWithAttributes:
[NSDictionary dictionaryWithObject:font forKey:NSFontAttributeName]];
CGPoint center = field.center;
CGRect frame = field.frame;
frame.size = size; // or CGSizeMake(size.width + WIDTH_PADDING * 2, size.height + HEIGHT_PADDING * 2)
field.frame = frame;
field.center = center;
}

Answer 2

the problem is that you don't take into account the contentInset of the UITextField. Your code would be fine for a label not for a textfield.
for example: one way could be:
CGPoint originalCenter = self.textField.center;
UIFont* currentFont = [textField font];
CGSize oldSize = [self.textField.text sizeWithFont:currentFont];
CGSize newSize = [textFieldString sizeWithFont:currentFont];
CGRect finalFrame = self.textField.frame
finalFrame.size.width -= oldSize.width;
finalFrame.size.width += newSize.width;
finalFrame.size.height -= oldSize.height;
finalFrame.size.height += newSize.height;
[self.textField setFrame:finalFrame];
[self.textField setCenter:originalCenter];
ios7 deprecates sizeWithFont:currentFont so it is sizeWithAttributes:#{NSFontAttributeName:currentFont}