iOS 限制UITextField输入文本长度

• (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
  if ([textField isEqual:alcoholConsumptionTF] ) {
  if (textField.text.length>=5) {
  NSString *string = [textField.text substringToIndex:5];//截取范围内的字符串
  textField.text=string;
  return NO;
  }
  }
  }