Question

是否有使用dispatch_sync和dispatch_after混合的最佳方式？

我必须遍历一个Views列表，然后等待加载数据。然后进一步滚动并等待加载数据。等等。

除非此dispatch_sync已完成，否则我不想执行其余的代码行。

参考代码：假设：

“aFinalListToRender”是我已过滤的视图列表，我想在我的上下文中呈现。

我已经确定了上下文的图像大小。

        UIGraphicsBeginImageContextWithOptions ? UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0):UIGraphicsBeginImageContext(imageSize);

        CGContextRef context = UIGraphicsGetCurrentContext();
        // Render the layer for the image.

        for (UIView *view in aFinalListToRender) {
            if ([view isKindOfClass:[UIScrollView class]]) {
                UIScrollView *aView = (UIScrollView *)view;
                for (int i = 0; i < ceil(aView.contentSize.height/aView.frame.size.height); i++) {
                    for (int j = 0; j <= ceil(aView.contentSize.width/aView.frame.size.width); j++) {
                        // Scroll smartly for retina and non-retina devices
                        [aView scrollRectToVisible:CGRectMake(aView.frame.size.width * j, aView.frame.size.height * i - (isRetina ? kRetinaValue: 0), aView.frame.size.width, aView.frame.size.height) animated:NO];

                        // TODO: Need to apply a synchronous-yet-asynchronous wait such that, 
                        // the current execution of the method pauses here, 
                        // yet allowing main thread to complete the execution, like rendering images etc,.
                        [aView.layer renderInContext:context];
                    }
                }
            } else {
                [view.layer renderInContext:context];
            }
        }

        aReturnVal = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

有没有办法使用dispatch_sync和dispatch_after

0 个答案: