ios - 返回主线程时异步 UIView 内容不显示

Question

加载我的 UIViewController 时，我基本上是在页面中间放置一个微调器，直到内容加载完毕，然后返回主线程添加 subview :

- (void)viewDidLoad {

    [super viewDidLoad];

    UIActivityIndicatorView *aiv_loading = ... // etc

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Load content
        NSString *s_checkout = [[BRNetwork sharedNetwork] getCheckoutInstructionsForLocation:self.locBooking.location];
        UIView *v_invoice_content = [[BRNetwork sharedNetwork] invoiceViewForBooking:locBooking.objectId];

        // Display the content
        dispatch_sync(dispatch_get_main_queue(), ^{

            if (s_checkout && v_invoice_content) {
                [aiv_loading removeFromSuperview];
                [self showContentWithText:s_checkout AndInvoice:v_invoice_content];
            } else {
                NSLog(@"No data received!"); // is thankfully not called
            }
        });
    });
}

- (void) showContentWithText:(NSString *)s_checkout AndInvoice:(UIView *)v_invoice {

    [self.view addSubview:[self checkoutTextWithText:s_checkout]]; // Most of the time displayed text
    [self.view addSubview:[self completeCheckout]]; // always Displayed UIButton
    [self.view addSubview:[self divider]]; // always displayed UIImageView

    // Summary title
    UILabel *l_summary = [[UILabel alloc] initWithFrame:CGRectMake(0, [self divider].frame.origin.y + 6 + 10, self.view.bounds.size.width, 20)];
    l_summary.text = NSLocalizedString(@"Summary", nil);
    [self.view addSubview:l_summary];

    CGRect totalRect = CGRectMake([self divider].frame.origin.x, [self divider].frame.origin.y + 6 + 30, self.view.bounds.size.width - [self divider].frame.origin.x, 90);
    _v_invoice = v_invoice;
    _v_invoice.frame = totalRect;
    [self.view addSubview:[self v_invoiceWithData:v_invoice]]; // THIS Pretty much never displayed

    UITextView *l_invoice = [[UITextView alloc] initWithFrame:CGRectMake(0, _v_invoice.frame.origin.y + _v_invoice.frame.size.height + offset, 320.0, 50)];
    l_invoice.text = NSLocalizedString(@"summary_emailed", nil);
    [self.view addSubview:l_invoice]; // Always displayed
}

但是，并不是所有的内容都显示出来。发票一开始是不存在的，但会在几分钟后显示出来。另一个异步创建的字符串 s_content 有时不显示。

这似乎是随机的内容创建。最终结果非常简洁，但对于生产版本而言并不可靠。

我使用未记录的 [self.view recursiveDescription] 来检查是否所有内容都在那里，即使我没有看到，它们都在那里，并且似乎是正确的框架。

有什么指点吗？- layoutSubviews 没有帮助!- 将背景颜色添加到发票 View 显示背景颜色

Answer 1

我怀疑这一行是你的问题:

UIView *v_invoice_content = [[BRNetwork sharedNetwork] invoiceViewForBooking:locBooking.objectId];

正如您在后台调度队列中调用它一样。任何涉及 UIKit 的工作都应该在主队列/线程上完成。要么将其移动到主线程 block 中，要么如果构建 View 依赖于来自网络调用的数据，请更改您的 invoiceViewForBooking 方法以首先返回数据，然后在主线程中构建您的 View 数据。

   dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Load content
        NSString *s_checkout = [[BRNetwork sharedNetwork] getCheckoutInstructionsForLocation:self.locBooking.location];
        id someData = [[BRNetwork sharedNetwork] invoiceDataForBooking:locBooking.objectId];

        // Display the content
        dispatch_async(dispatch_get_main_queue(), ^{
            UIView *v_invoice_content = [invoiceViewWithData:someData];
        });
    });

我还建议在主队列上使用 dispatch_async 而不是 dispatch_sync。