iOS實現旋轉

#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);  //逆時針旋轉
  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</pre>