UIView动画分析

 1 // UIView动画分析
 2
 3 #import "ViewController.h"
 4
 5 @interface ViewController ()
 6
 7 @property (nonatomic,strong) UIView *myView;
 8
 9 @end
10
11 @implementation ViewController
12
13
14
15 // 懒加载是get方法啊
16 -(UIView *)myView{
17     if (_myView == nil) {
18         _myView = [[UIView alloc]init];
19         _myView.backgroundColor = [UIColor orangeColor];
20         _myView.frame = CGRectMake(100, 100, 100, 100);
21     }
22     return _myView;
23 }
24
25
26
27 -(void)viewDidLoad {
28     [super viewDidLoad];
29     self.myView.center = CGPointMake(self.view.center.x, 0);
30      [self.view addSubview:_myView];
31 }
32
33 -(void)touchesBegan:(nonnull NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event{
34
35     NSLog(@"begin");
36     [UIView animateWithDuration:2.0 delay:0.0 usingSpringWithDamping:0.5 initialSpringVelocity:10.0 options:0 animations:^{
37         NSLog(@"开始动画");
38         self.myView.center = self.view.center;
39     } completion:^(BOOL finished) {
40         NSLog(@"完成动画");
41     }];
42     NSLog(@"over");
43
44 }
45 @end

结论：

block是一个C语言的预先准备好的代码在需要的时候执行。而UIView系统封装的动画是立即执行。所以在回调中写了代码后就立马执行的。一开始是begin，接下来是开始动画，然后异步over，再完成动画。