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304 lines
11 KiB
Markdown
304 lines
11 KiB
Markdown
# 终极截屏
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- **-(void)snapshotForView:(__kindof UIView *)view;**
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今天新学到这种写法，__kindof 是苹果声明的一个特性，是 Xcode7 出现的新特性。
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- 假如我们想声明一个方法，这个方法的参数必须是一个 UIView 类型的对象，那么我们应该可以写成下面这个样子
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```
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-(void)snapshotForView:(UIView *)view;
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```
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- 那么我们想声明一个方法，这个方法的参数必须是 UIView 及其 UIView 的子类，那么前一种写法就满足不了我们的需求了，这时候引入了 __kindof 方法
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```
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-(void)snapshotForView:(__kindof UIView *)view;
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```
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**UIWebView 截图**
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对 UIWebView 截图比较简单，renderInContext 这个方法相信大家都不会陌生，这个方法是 CALayer 的一个实例方法，可以用来对大部分 View 进行截图。我们知道，UIWebView 承载内容的其实是作为其子 View 的 UIScrollView，所以对 UIWebView 截图应该对其 scrollView 进行截图。具体的截图方法如下：
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```
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- (void)snapshotForScrollView:(UIScrollView *)scrollView
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{
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// 1. 记录当前 scrollView 的偏移和位置
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CGPoint currentOffset = scrollView.contentOffset;
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CGRect currentFrame = scrollView.frame;
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scrollView.contentOffset = CGPointZero;
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// 2. 将 scrollView 展开为其实际内容的大小
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scrollView.frame = CGRectMake(0, 0, scrollView.contentSize.width, scrollView.contentSize.height);
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// 3. 第三个参数设置为 0 表示设置为屏幕的默认缩放因子
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UIGraphicsBeginImageContextWithOptions(scrollView.contentSize, YES, 0);
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[scrollView.layer renderInContext:UIGraphicsGetCurrentContext()];
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UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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// 4. 重新设置 scrollView 的偏移和位置，还原现场
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scrollView.contentOffset = currentOffset;
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scrollView.frame = currentFrame;
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}
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```
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**WKWebView 截图**
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虽然 WKWebView 里也有 scrollView，但是直接对这个 scrollView 截图得到的是一片空白的，具体原因不明。一番 Google 之后可以看到好些人提到 drawViewHierarchyInRect 方法， 可以看到这个方法是 iOS 7.0 开始引入的。官方文档中描述为：
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> Renders a snapshot of the complete view hierarchy as visible onscreen into the current context.
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注意其中的 **visible onscreen**，也就是将屏幕中可见部分渲染到上下文中，这也解释了为什么对 WKWebView 中的 scrollView 展开为实际内容大小，再调用 drawViewHierarchyInRect 方法总是得到一张不完整的截图（只有屏幕可见区域被正确截到，其他区域为空白）。
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不过，这样倒是给我们提供了一个思路，可以将 WKWebView 按屏幕高度裁成 n 页，然后将 WKWebView 一页一页的往上推，每推一页就调用一次 drawViewHierarchyInRect 将当前屏幕的截图渲染到上下文中，最后调用 UIGraphicsGetImageFromCurrentImageContext 从上下文中获取的图片即为完整截图。
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核心代码如下：
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```
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- (void)snapshotForWKWebView:(WKWebView *)webView
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{
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// 1
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UIView *snapshotView = [webView snapshotViewAfterScreenUpdates:YES];
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[webView.superview addSubview:snapshotView];
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// 2
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CGPoint currentOffset = webView.scrollView.contentOffset;
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...
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// 3
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UIView *containerView = [[UIView alloc] initWithFrame:webView.bounds];
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[webView removeFromSuperview];
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[containerView addSubview:webView];
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// 4
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CGSize totalSize = webView.scrollView.contentSize;
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NSInteger page = ceil(totalSize.height / containerView.bounds.size.height);
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webView.scrollView.contentOffset = CGPointZero;
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webView.frame = CGRectMake(0, 0, containerView.bounds.size.width, webView.scrollView.contentSize.height);
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UIGraphicsBeginImageContextWithOptions(totalSize, YES, UIScreen.mainScreen.scale);
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[self drawContentPage:0 maxIndex:page completion:^{
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UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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// 8
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[webView removeFromSuperview];
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...
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}];
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}
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- (void)drawContentPage(NSInteger)index maxIndex:(NSInteger)maxIndex completion:(dispatch_block_t)completion
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{
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// 5
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CGRect splitFrame = CGRectMake(0, index * CGRectGetHeight(containerView.bounds), containerView.bounds.size.width, containerView.frame.size.height);
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CGRect myFrame = webView.frame;
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myFrame.origin.y = -(index * containerView.frame.size.height);
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webView.frame = myFrame;
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// 6
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[targetView drawViewHierarchyInRect:splitFrame afterScreenUpdates:YES];
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// 7
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if (index < maxIndex) {
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[self drawContentPage:index + 1 maxIndex:maxIndex completion:completion];
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} else {
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completion();
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}
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}
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```
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代码注意项如下（对应代码注释中的序号）：
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1. 为了截图时对 frame 进行操作不会出现闪屏等现象，我们需要盖一个“假”的 webView 到现在的位置上，并将真正的 webView “摘下来”。调用 snapshotViewAfterScreenUpdates 即可得到这样一个“假”的 webView
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2. 保存真正的 webView 的偏移、位置等信息，以便截图完成之后“还原现场”
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3. 用一个新的视图承载“真正的” webView，这个视图也是绘图所用到的上下文
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4. 将 webView 按照实际内容高度和屏幕高度分成 page 页
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5. 得到每一页的实际位置，并将 webView 往上推到该位置
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6. 调用 drawViewHierarchyInRect 将当前位置的 webView 渲染到上下文中
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7. 如果还未到达最后一页，则递归调用 drawViewHierarchyInRect 方法进行渲染；如果已经渲染完了全部页，则回调通知截图完成
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8. 调用 UIGraphicsGetImageFromCurrentImageContext 方法从当前上下文中获取到完整截图，将第 2 步中保存的信息重新赋予到 webView 上，“还原现场”
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注意：我们的截图方法中有对 webView 的 frame 进行操作，如果其他地方如果有对 frame 进行操作的话，是会影响我们截图的。所以在截图时应该禁用掉其他地方对 frame 的改变，就像这样：
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```
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- (void)layoutWebView
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{
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if (!_isCapturing) {
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self.wkWebView.frame = [self frameForWebView];
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}
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}
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```
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```
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#import <UIKit/UIKit.h>
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@class PPSnapshotHandler;
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@protocol PPSnapshotHandlerDelegate <NSObject>
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@optional
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- (void)snapshotHandler:(PPSnapshotHandler *)snapshotHandler didFinish:(UIImage *)captureImage forView:(UIView *)view;
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@end
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@interface PPSnapshotHandler : NSObject
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+ (instancetype)defaultHandler;
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@property (nonatomic, weak) id<PPSnapshotHandlerDelegate> delegate;
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- (void)snapshotForView:(__kindof UIView *)view;
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@end
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#import "PPSnapshotHandler.h"
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#import <WebKit/WebKit.h>
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#define DELAY_TIME_DRAW 0.1
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@interface PPSnapshotHandler () {
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BOOL _isCapturing;
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UIView *_captureView;
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}
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@end
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@implementation PPSnapshotHandler
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+ (instancetype)defaultHandler
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{
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static dispatch_once_t onceToken;
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static PPSnapshotHandler *defaultHandler = nil;
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dispatch_once(&onceToken, ^{
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defaultHandler = [[PPSnapshotHandler alloc] init];
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});
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return defaultHandler;
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}
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#pragma mark - public method
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- (void)snapshotForView:(__kindof UIView *)view
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{
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if (!view || _isCapturing) {
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return;
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}
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_captureView = view;
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if ([view isKindOfClass:[UIScrollView class]]) {
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[self snapshotForScrollView:(UIScrollView *)view];
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} else if ([view isKindOfClass:[UIWebView class]]) {
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UIWebView *webView = (UIWebView *)view;
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[self snapshotForScrollView:webView.scrollView];
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} else if ([view isKindOfClass:[WKWebView class]]) {
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[self snapshotForWKWebView:(WKWebView *)view];
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}
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}
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#pragma mark - WKWebView
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- (void)snapshotForWKWebView:(WKWebView *)webView
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{
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UIView *snapshotView = [webView snapshotViewAfterScreenUpdates:YES];
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snapshotView.frame = webView.frame;
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[webView.superview addSubview:snapshotView];
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CGPoint currentOffset = webView.scrollView.contentOffset;
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CGRect currentFrame = webView.frame;
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UIView *currentSuperView = webView.superview;
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NSUInteger currentIndex = [webView.superview.subviews indexOfObject:webView];
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UIView *containerView = [[UIView alloc] initWithFrame:webView.bounds];
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[webView removeFromSuperview];
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[containerView addSubview:webView];
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CGSize totalSize = webView.scrollView.contentSize;
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NSInteger page = ceil(totalSize.height / containerView.bounds.size.height);
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webView.scrollView.contentOffset = CGPointZero;
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webView.frame = CGRectMake(0, 0, containerView.bounds.size.width, webView.scrollView.contentSize.height);
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UIGraphicsBeginImageContextWithOptions(totalSize, YES, UIScreen.mainScreen.scale);
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[self drawContentPage:containerView webView:webView index:0 maxIndex:page completion:^{
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UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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[webView removeFromSuperview];
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[currentSuperView insertSubview:webView atIndex:currentIndex];
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webView.frame = currentFrame;
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webView.scrollView.contentOffset = currentOffset;
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[snapshotView removeFromSuperview];
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self->_isCapturing = NO;
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if (self.delegate && [self.delegate respondsToSelector:@selector(snapshotHandler:didFinish:forView:)]) {
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[self.delegate snapshotHandler:self didFinish:snapshotImage forView:self->_captureView];
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}
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}];
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}
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- (void)drawContentPage:(UIView *)targetView webView:(WKWebView *)webView index:(NSInteger)index maxIndex:(NSInteger)maxIndex completion:(dispatch_block_t)completion
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{
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CGRect splitFrame = CGRectMake(0, index * CGRectGetHeight(targetView.bounds), targetView.bounds.size.width, targetView.frame.size.height);
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CGRect myFrame = webView.frame;
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myFrame.origin.y = -(index * targetView.frame.size.height);
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webView.frame = myFrame;
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dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(DELAY_TIME_DRAW * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
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[targetView drawViewHierarchyInRect:splitFrame afterScreenUpdates:YES];
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if (index < maxIndex) {
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[self drawContentPage:targetView webView:webView index:index + 1 maxIndex:maxIndex completion:completion];
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} else {
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completion();
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}
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});
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}
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#pragma mark - UIScrollView
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- (void)snapshotForScrollView:(UIScrollView *)scrollView
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{
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CGPoint currentOffset = scrollView.contentOffset;
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CGRect currentFrame = scrollView.frame;
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scrollView.contentOffset = CGPointZero;
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scrollView.frame = CGRectMake(0, 0, scrollView.contentSize.width, scrollView.contentSize.height);
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UIGraphicsBeginImageContextWithOptions(scrollView.contentSize, YES, UIScreen.mainScreen.scale);
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[scrollView.layer renderInContext:UIGraphicsGetCurrentContext()];
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UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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scrollView.contentOffset = currentOffset;
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scrollView.frame = currentFrame;
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if (self.delegate && [self.delegate respondsToSelector:@selector(snapshotHandler:didFinish:forView:)]) {
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[self.delegate snapshotHandler:self didFinish:snapshotImage forView:_captureView];
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}
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}
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@end
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```
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