iOS中如何獲取某個視圖的截圖詳析

/**
 普通的截圖
 該API僅可以在未使用layer和OpenGL渲染的視圖上使用
 
 @return 截取的圖片
 */
- (UIImage *)nomalSnapshotImage
{
 UIGraphicsBeginImageContextWithOptions(self.frame.size, NO, [UIScreen mainScreen].scale);
 [self.layer renderInContext:UIGraphicsGetCurrentContext()];
 UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 
 return snapshotImage;
}

/**
 針對有用過OpenGL渲染過的視圖截圖
 
 @return 截取的圖片
 */
- (UIImage *)openglSnapshotImage
{
 CGSize size = self.bounds.size;
 UIGraphicsBeginImageContextWithOptions(size, NO, [UIScreen mainScreen].scale);
 CGRect rect = self.frame;
 [self drawViewHierarchyInRect:rect afterScreenUpdates:YES];
 UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 
 return snapshotImage;
}

/**
 截圖
 以UIView 的形式返回(_UIReplicantView)
 
 @return 截取出來的圖片轉(zhuǎn)換的視圖
 */
- (UIView *)snapshotView
{
 UIView *snapView = [self snapshotViewAfterScreenUpdates:YES];
 return snapView;
}

- (UIImage *)imageForWebView
{
 // 1.獲取WebView的寬高
 CGSize boundsSize = self.bounds.size;
 CGFloat boundsWidth = boundsSize.width;
 CGFloat boundsHeight = boundsSize.height;

 // 2.獲取contentSize
 CGSize contentSize = self.scrollView.contentSize;
 CGFloat contentHeight = contentSize.height;
 // 3.保存原始偏移量，便于截圖后復(fù)位
 CGPoint offset = self.scrollView.contentOffset;
 // 4.設(shè)置最初的偏移量為(0,0);
 [self.scrollView setContentOffset:CGPointMake(0, 0)];

 NSMutableArray *images = [NSMutableArray array];
 while (contentHeight > 0) {
  // 5.獲取CGContext 5.獲取CGContext
  UIGraphicsBeginImageContextWithOptions(boundsSize, NO, 0.0);
  CGContextRef ctx = UIGraphicsGetCurrentContext();
  // 6.渲染要截取的區(qū)域
  [self.layer renderInContext:ctx];
  UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  // 7.截取的圖片保存起來
  [images addObject:image];

  CGFloat offsetY = self.scrollView.contentOffset.y;
  [self.scrollView setContentOffset:CGPointMake(0, offsetY + boundsHeight)];
  contentHeight -= boundsHeight;
 }
 // 8 webView 恢復(fù)到之前的顯示區(qū)域
 [self.scrollView setContentOffset:offset];
 CGFloat scale = [UIScreen mainScreen].scale;
 CGSize imageSize = CGSizeMake(contentSize.width * scale,
         contentSize.height * scale);
 // 9.根據(jù)設(shè)備的分辨率重新繪制、拼接成完整清晰圖片
 UIGraphicsBeginImageContext(imageSize);
 [images enumerateObjectsUsingBlock:^(UIImage *image, NSUInteger idx, BOOL *stop) {
  [image drawInRect:CGRectMake(0,scale * boundsHeight * idx,scale * boundsWidth,scale * boundsHeight)];
 }];
 UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();
 
 return fullImage;
}