iOS如何将字符串中特定后的字变成红色

- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
  UILabel *testLabel=[[UILabel alloc]initWithFrame:CGRectMake(10, 100, 100, 50)];
  testLabel.text=@"1234567890";
  testLabel.backgroundColor=[UIColor orangeColor];
  [self.view addSubview:testLabel];
  [self redXingWithLabel:testLabel atIndex:2];
}
//将字符串特定的1个字变成红色
- (void)redXingWithLabel:(UILabel *)tempLabel atIndex:(NSInteger)tempIndex {
  NSMutableAttributedString * tempString = [[NSMutableAttributedString alloc] initWithString: tempLabel.text];
  [tempString addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(tempIndex, 1)];
  tempLabel.attributedText = tempString;
}