UIScrollView setNeedsDisplay 不起作用，还是其他什么？

Question

此问题的最终解决方案在问题下方给出

我的目标是创建一个图像选择器，该图像选择器最初在滚动视图内创建每个图像视图，然后将该图像视图的引用传递给一种使用适当图像异步更新 imageview.image 的方法。

这很好用。

我遇到的问题是滚动视图仅显示图像视图在方法结束时批量处理，而我希望它们在创建时一张一张地打印（图像是否可用）。

如果我触摸滚动视图进行滚动，它会按照我想要的方式工作，但如果我根本不触摸，屏幕将保持白色，直到所有图像（而不仅仅是图像视图）都显示出来。加载完成。

我尝试将 setNeedsDisplay 放置在每个视图的任何地方，包括 self.view、scrollview 和每个单独的 imageview。这是怎么回事？

- (void)viewDidLoad {
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
     dispatch_async(queue, ^{
          [self setGridView];
     });
}

- (void)setGridView {
    // begin loading images
    NSString * retina = ([[MVProject sharedInstance] settings_retina]) ? @"2" : @"";

    CGRect scrollframe = CGRectMake(0, 0, 300, 275);
    UIScrollView * newscrollview;
    newscrollview = [[UIScrollView alloc] initWithFrame:scrollframe];
    newscrollview.scrollEnabled = YES;
    newscrollview.delegate = self;
    [newscrollview setContentSize:CGSizeMake(300, (((ceilf([[NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"Flickr_Dictionary"]] count]/4)) * (58+15)) + 15 + 58 + 15))];
    [picsMVContentCell.contentView addSubview:newscrollview];

    float currentx = 11;
    float currenty = 17;
    NSInteger index = 0;

    for (NSDictionary * d in [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"Flickr_Dictionary"]]) {

        // create button
        UIButton * button = [UIButton buttonWithType:UIButtonTypeCustom];
        button.frame = CGRectMake(currentx, currenty, 58, 58);
        button.imageView.backgroundColor = [UIColor colorWithRed:(241/255.0) green:(241/255.0) blue:(241/255.0) alpha:1];
        button.imageView.contentMode = UIViewContentModeScaleAspectFit;
        button.imageView.layer.cornerRadius = 6;
        button.imageView.layer.masksToBounds = YES;
        button.imageView.accessibilityLabel = [d objectForKey:@"id"];
        button.imageView.accessibilityValue = [d objectForKey:@"full"];
        button.imageView.tag = index++;
        [button addTarget:self action:@selector(imageClick:) forControlEvents:UIControlEventTouchUpInside];

        UIImage * image = [MVImage imageWithImage:[UIImage imageNamed:@""] covertToWidth:58.0f covertToHeight:58.0f];
        [button setImage:image forState:UIControlStateNormal];

        [newscrollview addSubview:button];
        [newscrollview bringSubviewToFront:button];
        [newscrollview setNeedsDisplay];

        // calculate next image view position
        currentx += (button.imageView.frame.size.width+15);
        if (currentx >= 289) {
            currentx = 11;
            currenty += (button.imageView.frame.size.height+15);
        }

        // set image
        NSString * nsuserdefault = [NSString stringWithFormat:@"Settings_SFThumbs%@_%@", retina, [d objectForKey:@"id"]];
        if ([NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]]) {
            MVImage * thumb = [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]];
            [button setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f] forState:UIControlStateNormal];
        } else {
            [MVProject asynchronousImageLoad:button.imageView urlpath:[d objectForKey:@"thumb"] nsuserdefaultpath:nsuserdefault];
        }
    }
}

于 2012 年 2 月 7 日下午 3:26 编辑

这些更改解决了与问题中给出的代码相关的所有问题，

感谢 @Eugene 为我指明了正确的方向

/* ---------- ---------- ---------- ---------- ---------- */

- (void)viewDidLoad {
     [super viewDidLoad];

     [[MVProject sharedInstance] syncLoadSF:0];

    self.newscrollview = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 300, 275)];
    self.newscrollview.scrollEnabled = YES;
    self.newscrollview.delegate = self;
    [self.newscrollview setContentSize:CGSizeMake(300, (((ceilf(([[NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"Flickr_Dictionary"]] count]-1)/4)) * (58+15)) + 15 + 58 + 15))];
    [picsMVContentCell.contentView addSubview:self.newscrollview];

    [self setGridView];
}

/* ---------- ---------- ---------- ---------- ---------- */

- (void)setGridView {
    NSString * retina = ([[MVProject sharedInstance] settings_retina]) ? @"2" : @"";
    [self.newscrollview setNeedsDisplay];
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul);
    dispatch_async(queue, ^{
        NSInteger index = 0;
        for (NSDictionary * d in [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:@"Flickr_Dictionary"]]) {
            // create button
            UIButton * button = [UIButton buttonWithType:UIButtonTypeCustom];               
            button.frame = CGRectMake((11 + ((index%4)*(58+15))), (17 + ((floorf(index/4))*(58+15))), 58, 58);
            button.imageView.backgroundColor = [UIColor colorWithRed:(241/255.0) green:(241/255.0) blue:(241/255.0) alpha:1];
            button.imageView.contentMode = UIViewContentModeScaleAspectFit;
            button.imageView.layer.cornerRadius = 3;
            button.imageView.layer.masksToBounds = YES;
            button.imageView.accessibilityLabel = [d objectForKey:@"id"];
            button.imageView.accessibilityValue = [d objectForKey:@"full"];
            button.imageView.tag = index++;
            [button addTarget:self action:@selector(imageClick:) forControlEvents:UIControlEventTouchUpInside];

            dispatch_sync(dispatch_get_main_queue(), ^ {
                [button setImage:[MVImage imageWithImage:[UIImage imageNamed:@""] covertToWidth:58.0f covertToHeight:58.0f] forState:UIControlStateNormal];
                [self.newscrollview addSubview:button];
                [self.newscrollview bringSubviewToFront:button];
                [self.newscrollview setNeedsDisplay];

                // set image
                NSString * nsuserdefault = [NSString stringWithFormat:@"Settings_SFThumbs%@_%@", retina, [d objectForKey:@"id"]];
                if ([NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]]) {
                    MVImage * thumb = [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]];
                    [button setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f] forState:UIControlStateNormal];
                } else {
                    [MVProject asynchronousImageLoad:button.imageView urlpath:[d objectForKey:@"thumb"] nsuserdefaultpath:nsuserdefault];
                }
            });
        }
    });
    [self.newscrollview setNeedsDisplay];
}

Answer 1

您无法在后台线程上进行绘图。每次添加子视图时，您都应该在主线程中执行此操作。因此，对您的救赎是在同步块中使用绘图代码，该代码在主队列上运行

  dispatch_sync(dispatch_get_main_queue(), ^ {
    [newscrollview addSubview:button];
    [newscrollview bringSubviewToFront:button];
    [newscrollview setNeedsDisplay];

    // calculate next image view position
    currentx += (button.imageView.frame.size.width+15);
    if (currentx >= 289) {
      currentx = 11;
      currenty += (button.imageView.frame.size.height+15);
    }

    // set image
    NSString * nsuserdefault = [NSString stringWithFormat:@"Settings_SFThumbs%@_%@", retina, [d objectForKey:@"id"]];
    if ([NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]]) {
      MVImage * thumb = [NSKeyedUnarchiver unarchiveObjectWithData:[[NSUserDefaults standardUserDefaults] objectForKey:nsuserdefault]];
      [button setImage:[MVImage imageWithImage:[[UIImage alloc] initWithData:thumb.data] covertToWidth:58.0f covertToHeight:58.0f] forState:UIControlStateNormal];
    } else {
      [MVProject asynchronousImageLoad:button.imageView urlpath:[d objectForKey:@"thumb"] nsuserdefaultpath:nsuserdefault];
    }
  });

Answer 2

您遇到的问题是设置图像。您想要做的是将所有图像容器添加到滚动视图中。然后，当图像准备好时，将它们加载到容器中。有两种方法可以做到这一点。

首先将所有容器添加到滚动视图中。 （您可能需要一些加载指示器或默认图像来显示其加载）

1) 创建一个后台线程来准备图像。当图像准备好后，将其添加到其容器中。 （我发现这种方式需要更多工作，而且有点痛苦）

2）创建一个自定义容器，并让自定义容器在其图像准备好时添加自己的图像。

例如，我正在从服务器加载图像。所以我创建了 AsyncImage 类，它是 UIImageView 的自定义类。我创建了一个函数，将图像 url 发送到其中，它会处理其余的事情。它创建一个 NSURLConnection，并在加载数据时调用 self.image = [UIImage imageWithData:data];