写入完成块的方法

Question

我刚开始尝试使用块，我对创建自己的完成块的方法很感兴趣。到目前为止，我阅读了 appCoda 的教程和 stackoverflow 的这篇文章： Custom Completion Block For My Own Method

这是我尝试实现它的一个例子：

#import "MainViewController.h"

@interface MainViewController ()
{
    UIImageView *animationView;
}
typedef void(^myCompletion)(BOOL);
@end

@implementation MainViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    //Set the backgroun image
    UIImageView *backgroundImage = [[UIImageView alloc] initWithFrame:CGRectMake(0, 20.0f, [[UIScreen mainScreen] bounds].size.width, [[UIScreen mainScreen] bounds].size.height - 20.f)];
    [backgroundImage setImage:[UIImage imageNamed:@"chalk_board_texture_by_blueamnesiac-d4h76qm.png"]];
    [self.view addSubview:backgroundImage];


    [self myMethod:^(BOOL finished) {
        if(finished){
            [animationView setImage:[UIImage imageNamed:@"Animation60.png"]];
        }
    }];
}

-(void) myMethod:(myCompletion) compblock{
    //do stuff
    //Get the imges name into array
    NSArray *imageNames = @[@"Animation1.png", @"Animation2.png", @"Animation3.png", @"Animation4.png",
                            @"Animation5.png", @"Animation6.png", @"Animation7.png", @"Animation8.png",
                            @"Animation9.png", @"Animation10.png", @"Animation11.png", @"Animation12.png",
                            @"Animation13.png", @"Animation14.png", @"Animation15.png", @"Animation16.png",
                            @"Animation17.png", @"Animation18.png", @"Animation19.png", @"Animation20.png",
                            @"Animation21.png", @"Animation22.png", @"Animation23.png", @"Animation24.png",
                            @"Animation25.png", @"Animation26.png", @"Animation27.png", @"Animation28.png",
                            @"Animation29.png", @"Animation30.png", @"Animation31.png", @"Animation32.png",
                            @"Animation33.png", @"Animation34.png", @"Animation35.png", @"Animation36.png",
                            @"Animation37.png", @"Animation38.png", @"Animation39.png", @"Animation40.png",
                            @"Animation41.png", @"Animation42.png", @"Animation43.png", @"Animation44.png",
                            @"Animation45.png", @"Animation46.png", @"Animation47.png", @"Animation48.png",
                            @"Animation49.png", @"Animation50.png", @"Animation51.png", @"Animation52.png",
                            @"Animation53.png", @"Animation54.png", @"Animation55.png", @"Animation56.png",
                            @"Animation57.png", @"Animation58.png", @"Animation59.png", @"Animation60.png",];

    //move image objects by name to mutable array
    NSMutableArray *images = [[NSMutableArray alloc] init];
    for (int i = 0; i < imageNames.count; i++) {
        [images addObject:[UIImage imageNamed:[imageNames objectAtIndex:i]]];
    }

    //Create the image horlder for the animation using the window size
    int animationViewWidth = [[UIScreen mainScreen] bounds].size.width - 20.0f;
    int animationViewHeight = animationViewWidth * 1.38;
    animationView = [[UIImageView alloc]initWithFrame:CGRectMake(10.0f, 20.0f, animationViewWidth, animationViewHeight)];
    animationView.animationImages = images;
    animationView.animationDuration = 0.5;
    animationView.animationRepeatCount = 1;
    [self.view addSubview:animationView];
    [animationView startAnimating];

    //completion finished set bool to yes
    compblock(YES);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end

完成处理程序中的错误是它在动画完成后没有设置背景图像。 提前致谢！

到目前为止，我找到了两个很好的答案： 来自@Rob 的那个： - 将图像视图的图像属性设置为 startAnimating 之前的第 60 个图像。

还有来自@ian-macdonald 的另一个重定向到我们同时发现的一个很棒的教程： - How to Animate Images in a UIImageView with Completion Handler

但问题仍然存在，为什么不能将块实现为侦听器，而当动画完成时，块会触发背景图像更改？

Answer 1

我认为您根本不需要完成的块。只需致电
[animationView setImage:[UIImage imageNamed:@"Animation60.png"]];
在触发动画之前，它会在动画完成后显示图像。不确定在动画开始之前是否会在很短的时间内显示最后一张图像（但我认为如果你立即开始动画则没有）。

Answer 2

您在告诉动画开始后立即调用compblock。动画还没来得及完成。

您可以监听动画完成，或者您可以假设它需要您请求的确切时间。

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
  compblock(YES);
});

您可能会在使用此方法时遇到一些未对齐的帧，因为动画可能需要更少或更多的时间，但它可能只是几毫秒并且完全不引人注意。

---

您可能对 uiimageview 动画图像补全的first hit on Google 感兴趣。相关代码块：

NSMutableArray *images = [[NSMutableArray alloc] init];
NSInteger animationImageCount = 38;
for (NSInteger i = 0; i < animationImageCount; i++) {
    // Images are numbered IndexedImagesInMyAnimation0, 1, 2, etc...
    [images addObject:(id)[UIImage imageNamed:[NSString stringWithFormat:@"IndexedImagesInMyAnimation%d", i]].CGImage];
}

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"contents"];
animation.calculationMode = kCAAnimationDiscrete;
animation.duration = animationImageCount / 24.0; // 24 frames per second
animation.values = images;
animation.repeatCount = 1;
animation.removedOnCompletion = NO;
animation.fillMode = kCAFillModeForwards;
[self.animationImageView.layer addAnimation:animation forKey:@"animation"];