Question

现在，我正在分配和初始化占据整个屏幕的三个UIImageView，并将它们堆叠在viewDidLoad方法中。它实际上需要一些时间来做到这一点。有没有办法自动执行此操作，以便视图在加载之前只有它们？像一个init方法会加快这个速度？

- (void)viewDidLoad {

[super viewDidLoad];

self.mySubviews = [[NSMutableArray alloc] init];
self.videoCounterTags = [[NSMutableArray alloc] init];

int c = (int)[self.scenes count];
c--;
NSLog(@"int c = %d", c);
self.myCounter = [NSNumber numberWithInt:c];


for (int i=0; i<=c; i++) {

    //create imageView
    UIImageView *imageView =[[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.height)];
    [imageView setUserInteractionEnabled:YES]; // <--- This is very important
    imageView.tag = i;                        // <--- Add tag to track this subview in the view stack
    [self.view addSubview:imageView];
    NSLog(@"added image view %d", i);


    //get scene object
    PFObject *sceneObject = self.scenes[i];


    //get the PFFile and filetype
    PFFile *file = [sceneObject objectForKey:@"file"];
    NSString *fileType = [sceneObject objectForKey:@"fileType"];



    //check the filetype
    if ([fileType  isEqual: @"image"])
    {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
        //get image
        NSURL *imageFileUrl = [[NSURL alloc] initWithString:file.url];
        NSData *imageData = [NSData dataWithContentsOfURL:imageFileUrl];
            dispatch_async(dispatch_get_main_queue(), ^{
        imageView.image = [UIImage imageWithData:imageData];
            });
        });

    }

    //its a video
    else
    {
        // the video player
        NSURL *fileUrl = [NSURL URLWithString:file.url];

        self.avPlayer = [AVPlayer playerWithURL:fileUrl];
        self.avPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;

        self.avPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:self.avPlayer];
        //self.avPlayerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(playerItemDidReachEnd:)
                                                     name:AVPlayerItemDidPlayToEndTimeNotification
                                                   object:[self.avPlayer currentItem]];

        CGRect screenRect = [[UIScreen mainScreen] bounds];

        self.avPlayerLayer.frame = CGRectMake(0, 0, screenRect.size.width, screenRect.size.height);
        [imageView.layer addSublayer:self.avPlayerLayer];

        NSNumber *tag = [NSNumber numberWithInt:i+1];

        NSLog(@"tag = %@", tag);

        [self.videoCounterTags addObject:tag];

    }


}



UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewTapped:)];

// dummyScreen is just a see through view that sits on top of my image stack and holds my tap gesture recognizer
[self.view bringSubviewToFront:self.dummyScreen];

[self.dummyScreen addGestureRecognizer:tapGesture];



}

Answer 1

问题在于这一行：

dispatch_async(dispatch_get_global_queue...

这会让你进入后台线程，因此无法确定何时执行代码。因此延迟。

如果这些是本地文件（即，网址是应用包中图片文件的文件网址），则不需要任何dispatch_async码。删除所有这些并在主线程上执行所有操作。这样，它会尽快发生。
如果这些是远程文件（即你必须要联网才能掌握它们），那么你可能无法做任何事情来加快速度;网络需要时间，viewDidLoad就在您可能被告知是时候抓住图像的时候。{/ p>

比viewDidLoad更快地设置子视图

1 个答案: