ios - 如何优化具有大量图像的 UIScrollView

Question

我一次加载了 UIScrollView 中的所有图像，我知道这是不好的方法，那么有没有更好的方法来优化它？

Answer 1

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    int currentPage = (scrollView.contentOffset.x / scrollView.frame.size.width);

    // display the image and maybe +/-1 for a smoother scrolling
    // but be sure to check if the image already exists, you can
    // do this very easily using tags
    if ([scrollView viewWithTag:(currentPage + 1)]) {
        return;
    } else {
        // view is missing, create it and set its tag to currentPage+1
        UIImageView *iv = [[UIImageView alloc] initWithFrame:
            CGRectMake((currentPage + 1) * scrollView.frame.size.width,
                       0,
                       scrollView.frame.size.width,
                       scrollView.frame.size.height)];
        iv.image = [UIImage imageNamed:[NSString stringWithFormat:@"%i.jpg",
                                                                  currentPage + 1]];
        iv.tag = currentPage + 1;
        [sv addSubview:iv];
    }

    /**
     * using your paging numbers as tag, you can also clean the UIScrollView
     * from no longer needed views to get your memory back
     * remove all image views except -1 and +1 of the currently drawn page
     */
    for (int i = 0; i < 50; i++) {
        if ((i < (currentPage - 1) || i > (currentPage + 1)) &&
            [scrollView viewWithTag:(i + 1)]) {
            [[scrollView viewWithTag:(i + 1)] removeFromSuperview];
        }
    }
}