iOS UIButton 显示不同的字体颜色

- (void)viewDidLoad {
    [super viewDidLoad];
    NSString * aStr = @"交流群246807516";
    NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@",aStr]];
    [str addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"Arial-BoldItalicMT" size:16.0] range:NSMakeRange(0,3)];
    [str addAttribute:NSForegroundColorAttributeName value:[UIColor greenColor]range:NSMakeRange(0,3)];
    
    UIButton * butn = [UIButton buttonWithType:UIButtonTypeCustom];
    butn.backgroundColor = [UIColor orangeColor];
    butn.frame = CGRectMake(100, 200, 200, 30);
    [butn setAttributedTitle:str forState:UIControlStateNormal];
    [butn addTarget:self action:@selector(click) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:butn];
}