限制textField长度

(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

if (textField == self.liveThemeTextField) {
//这里的if时候为了获取删除操作,如果没有次if会造成当达到字数限制后删除键也不能使用的后果.
if (range.length == 1 && string.length == 0) {
return YES;
}
//so easy
else if (self.liveThemeTextField.text.length >= 30) {
self.liveThemeTextField.text = [textField.text substringToIndex:30];
return NO;
}
}
return YES;
}