Initialize the UITextField with a CGRect as a frame:

Swift

let textfield = UITextField(frame: CGRect(x: 0, y: 0, width: 200, height: 21))

Objective-C

UITextField *textField = [[UITextField alloc] initWithFrame:CGRectMake(0, 0, 200, 21)];

You can also create a UITextField in Interface Builder:

http://i.stack.imgur.com/gWMCT.png