1. 场景： 在需要执行一个图片组动画时，如何保证动画结束后，图片从内存中消失

    2. 涉及到的核心方法：

      1. imageWithContentsOfFile:
      2. imageNamed:

    1. 总结：

      // 设置animationImages为空后： // 通过imageWithContentsOfFile:加载的图片数组会从内存中消失 - 适用于使用频次较低、大量的图片 // 通过imageNamed:方式加载的图片会持续保留在内存中（使用后在内存中有缓存） - 适用于经常使用，内存占用较小的图片的加载方式；放到Assets.xcassets的图片,默认就有缓存。

    Demo：

    1. #import "ViewController.h"
    3. @interface ViewController ()
    4. @property (nonatomic, strong) UIImageView *imageView;
    5. @end
    7. @implementation ViewController
    9. - (UIImageView *)imageView{
    10.     if (!_imageView) {
    11.         _imageView = [UIImageView new];
    12.         _imageView.backgroundColor = [UIColor darkGrayColor];
    13.         _imageView.contentMode = UIViewContentModeScaleAspectFit;
    14.     }
    15.     return _imageView;
    16. }
    19. - (void)viewDidLoad {
    20.     [super viewDidLoad];
    21.     // Do any additional setup after loading the view.
    23.     [self.view addSubview:self.imageView];
    24.     self.imageView.frame = CGRectInset(self.view.bounds, 10, 80);
    28.     UIStackView *stackView = [[UIStackView alloc] initWithFrame:CGRectMake(0, 40, 300, 40)];
    29.     stackView.axis = UILayoutConstraintAxisHorizontal;
    30.     stackView.distribution = UIStackViewDistributionFillEqually;
    31.     [self.view addSubview:stackView];
    32.     stackView.backgroundColor = [UIColor grayColor];
    34.     {
    35.         UIButton *btn1 = [UIButton new];
    36.         [btn1 setTitle:@"开始1" forState:UIControlStateNormal];
    37.         [btn1 addTarget:self action:@selector(start:) forControlEvents:UIControlEventTouchUpInside];
    38.         [stackView addArrangedSubview:btn1];
    39.     }
    40.     {
    41.         UIButton *btn1 = [UIButton new];
    42.         [btn1 setTitle:@"开始2" forState:UIControlStateNormal];
    43.         [btn1 addTarget:self action:@selector(start2:) forControlEvents:UIControlEventTouchUpInside];
    44.         [stackView addArrangedSubview:btn1];
    45.     }
    46.     {
    47.         UIButton *btn1 = [UIButton new];
    48.         [btn1 setTitle:@"结束" forState:UIControlStateNormal];
    49.         [btn1 addTarget:self action:@selector(end:) forControlEvents:UIControlEventTouchUpInside];
    50.         [stackView addArrangedSubview:btn1];
    51.     }
    52. }
    55. - (void)start:(UIButton *)sender{
    56.     NSMutableArray *images = [NSMutableArray array];
    57.     for (NSInteger i = 0; i<8; i++) {
    58.         NSString *fileName = [NSString stringWithFormat:@"moto_%03ld",i];
    59.         NSString *filePath = [[NSBundle mainBundle] pathForResource:fileName ofType:@"jpeg"];
    60.         [images addObject:[UIImage imageWithContentsOfFile:filePath]];
    61.     }
    63.     self.imageView.animationImages = images;
    64.     self.imageView.animationDuration = 8;
    65.     self.imageView.animationRepeatCount = 2;
    66.     [self.imageView startAnimating];
    67. }
    69. - (void)start2:(UIButton *)sender{
    71.     NSMutableArray *images = [NSMutableArray array];
    72.     for (NSInteger i = 0; i<8; i++) {
    73.         NSString *fileName = [NSString stringWithFormat:@"moto_%03ld",i];
    74.         [images addObject:[UIImage imageNamed:fileName]];
    75.     }
    77.     self.imageView.animationImages = images;
    78.     self.imageView.animationDuration = 8;
    79.     self.imageView.animationRepeatCount = 2;
    80.     [self.imageView startAnimating];
    81. }
    84. - (void)end:(UIButton *)sender{
    85.     [self.imageView stopAnimating];
    86.     // 设置animationImages为空后：
    87.     // 通过imageWithContentsOfFile:加载的图片数组会从内存中消失 - 适用于使用频次较低、大量的图片
    88.     // 通过imageNamed:方式加载的图片会持续保留在内存中（使用后在内存中有缓存） - 适用于经常使用，内存占用较小的图片的加载方式；放到Assets.xcassets的图片,默认就有缓存。
    89.     self.imageView.animationImages = nil;
    90. }
    94. @end