#import "ViewController.h"
 
@interface ViewController ()
@property (strong, nonatomic)UILabel *label;
@end
 
@implementation ViewController
 
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    CGRect labelFrame = CGRectMake(100, 100,100, 50);
    self.label = [[UILabel alloc] initWithFrame:labelFrame];
    self.label.font = [UIFont fontWithName:@"Helvetica" size:36];
    self.label.text = @"XxxX";
    self.label.textAlignment = NSTextAlignmentCenter;
    self.label.backgroundColor = [UIColor brownColor];
    [self.view addSubview:self.label];
    [self rotateLabelDown];
}
 
- (void)rotateLabelDown{
    [UIView animateWithDuration:10 animations:^{
        self.label.layer.anchorPoint = CGPointMake(0.5, 0.5);
        //self.label.transform = CGAffineTransformMakeRotation(-90);  //逆时针旋转
        self.label.transform = CGAffineTransformMakeRotation(M_PI);
    } completion:^(BOOL finished) {
        [self rotateLabelUp];
    }];
}
 
- (void)rotateLabelUp{
    [UIView animateWithDuration:10 animations:^{
        self.label.layer.anchorPoint = CGPointMake(0.5, 0.5);
        self.label.transform = CGAffineTransformMakeRotation(0);
    } completion:^(BOOL finished) {
        [self rotateLabelDown];
    }];
}
 
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
 
@end