代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    //把<br!>换成\n
    NSString *string=@"123<br!>456<br!>789";
    NSString *newStr=[string stringByReplacingOccurrencesOfString:@"<br!>" withString:@"\n"];
    NSString *newNewStr=[newStr stringByReplacingOccurrencesOfString:@"\n" withString:@"<br!>"];
    
    UILabel *label=[[UILabel alloc]initWithFrame:CGRectMake(10, 100, 100, 200)];
    label.backgroundColor=[UIColor redColor];
    label.text=newNewStr;
    //下面这个代码很重要，很重要的
    label.numberOfLines=0;
    [self.view addSubview:label];
}