iOS 截图的那些事儿

- (void)snapshotForScrollView:(UIScrollView *)scrollView
{
    // 1. 记录当前 scrollView 的偏移和位置
    CGPoint currentOffset = scrollView.contentOffset;
    CGRect currentFrame = scrollView.frame;

    scrollView.contentOffset = CGPointZero;
    // 2. 将 scrollView 展开为其实际内容的大小
    scrollView.frame = CGRectMake(0, 0, scrollView.contentSize.width, scrollView.contentSize.height);

    // 3. 第三个参数设置为 0 表示设置为屏幕的默认缩放因子
    UIGraphicsBeginImageContextWithOptions(scrollView.contentSize, YES, 0);
    [scrollView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    // 4. 重新设置 scrollView 的偏移和位置，还原现场
    scrollView.contentOffset = currentOffset;
    scrollView.frame = currentFrame;
}

- (void)snapshotForWKWebView:(WKWebView *)webView
{
    // 1
    UIView *snapshotView = [webView snapshotViewAfterScreenUpdates:YES];
    [webView.superview addSubview:snapshotView];

    // 2
    CGPoint currentOffset = webView.scrollView.contentOffset;
    ...

    // 3
    UIView *containerView = [[UIView alloc] initWithFrame:webView.bounds];
    [webView removeFromSuperview];
    [containerView addSubview:webView];

    // 4
    CGSize totalSize = webView.scrollView.contentSize;
    NSInteger page = ceil(totalSize.height / containerView.bounds.size.height);

    webView.scrollView.contentOffset = CGPointZero;
    webView.frame = CGRectMake(0, 0, containerView.bounds.size.width, webView.scrollView.contentSize.height);

    UIGraphicsBeginImageContextWithOptions(totalSize, YES, UIScreen.mainScreen.scale);
    [self drawContentPage:0 maxIndex:page completion:^{
        UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        // 8
        [webView removeFromSuperview];
        ...
    }];
}

- (void)drawContentPage(NSInteger)index maxIndex:(NSInteger)maxIndex completion:(dispatch_block_t)completion
{
    // 5
    CGRect splitFrame = CGRectMake(0, index * CGRectGetHeight(containerView.bounds), containerView.bounds.size.width, containerView.frame.size.height);
    CGRect myFrame = webView.frame;
    myFrame.origin.y = -(index * containerView.frame.size.height);
    webView.frame = myFrame;

    // 6
    [targetView drawViewHierarchyInRect:splitFrame afterScreenUpdates:YES];

    // 7
    if (index < maxIndex) {
        [self drawContentPage:index + 1 maxIndex:maxIndex completion:completion];
    } else {
        completion();
    }
}

- (void)layoutWebView
{
    if (!_isCapturing) {
        self.wkWebView.frame = [self frameForWebView];
    }
}