Ios xCode CGContextSaveGState:无效的上下文0x0错误

我刚刚将xCode更新为7.0。我的代码以前是有效的，但现在我得到了：

CGContextSaveGState:上下文0x0无效。如果要查看回溯，请设置CG_CONTEXT_SHOW_backtrace环境变量

在我的应用程序中，我有一个收件箱，一旦选中消息单元格，它就会显示图像/视频。在消息显示之前，它们显示良好，但在更新后，它们不再显示。这是一个有效的错误还是苹果的错误？下面是相关代码

InboxTableViewController.m

    - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    self.selectedMessage = [self.messages objectAtIndex:indexPath.row];

    // mark message as read
    NSMutableArray *readByIds = [NSMutableArray arrayWithArray:[self.selectedMessage objectForKey:@"readBy"]];

    if ([readByIds containsObject:[[PFUser currentUser] objectId]]) {
        // message has already been read. do nothing
    }else {
        // message was unread. mark it as read now.
        [readByIds addObject:[[PFUser currentUser] objectId]];
        [self.selectedMessage setObject:readByIds forKey:@"readBy"];
        [self.selectedMessage saveInBackground];
    }


    NSString *fileType = [self.selectedMessage objectForKey:@"fileType"];
    if ([fileType isEqualToString:@"image"]) {
        // file type is image
        [self performSegueWithIdentifier:@"showImage" sender:self];
    } else {
        // file type is video
        PFFile *videoFile = [self.selectedMessage objectForKey:@"file"];
        NSURL *fileUrl = [NSURL URLWithString:videoFile.url];
        self.moviePlayer.contentURL = fileUrl;
        [self.moviePlayer prepareToPlay];
        [self.moviePlayer thumbnailImageAtTime:0 timeOption:MPMovieTimeOptionNearestKeyFrame];

        // add it to the view controller so we can see it
        [self.view addSubview:self.moviePlayer.view];
        [self.moviePlayer setFullscreen:YES animated:YES];
    }

}

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *senderName = [self.message objectForKey:@"senderFullName"];
    self.navigationItem.title = senderName;

    // download image from Parse.com
    PFFile *imageFile = [self.message objectForKey:@"file"];
    NSURL *imageFileUrl = [[NSURL alloc] initWithString:imageFile.url];
    NSData *imageData = [NSData dataWithContentsOfURL:imageFileUrl];

    //set the image view to the message image
    self.imageView.image = [UIImage imageWithData:imageData];
}

ImageViewController.m

    - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    self.selectedMessage = [self.messages objectAtIndex:indexPath.row];

    // mark message as read
    NSMutableArray *readByIds = [NSMutableArray arrayWithArray:[self.selectedMessage objectForKey:@"readBy"]];

    if ([readByIds containsObject:[[PFUser currentUser] objectId]]) {
        // message has already been read. do nothing
    }else {
        // message was unread. mark it as read now.
        [readByIds addObject:[[PFUser currentUser] objectId]];
        [self.selectedMessage setObject:readByIds forKey:@"readBy"];
        [self.selectedMessage saveInBackground];
    }


    NSString *fileType = [self.selectedMessage objectForKey:@"fileType"];
    if ([fileType isEqualToString:@"image"]) {
        // file type is image
        [self performSegueWithIdentifier:@"showImage" sender:self];
    } else {
        // file type is video
        PFFile *videoFile = [self.selectedMessage objectForKey:@"file"];
        NSURL *fileUrl = [NSURL URLWithString:videoFile.url];
        self.moviePlayer.contentURL = fileUrl;
        [self.moviePlayer prepareToPlay];
        [self.moviePlayer thumbnailImageAtTime:0 timeOption:MPMovieTimeOptionNearestKeyFrame];

        // add it to the view controller so we can see it
        [self.view addSubview:self.moviePlayer.view];
        [self.moviePlayer setFullscreen:YES animated:YES];
    }

}

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *senderName = [self.message objectForKey:@"senderFullName"];
    self.navigationItem.title = senderName;

    // download image from Parse.com
    PFFile *imageFile = [self.message objectForKey:@"file"];
    NSURL *imageFileUrl = [[NSURL alloc] initWithString:imageFile.url];
    NSData *imageData = [NSData dataWithContentsOfURL:imageFileUrl];

    //set the image view to the message image
    self.imageView.image = [UIImage imageWithData:imageData];
}

随后，我纠正了我的错误

我特别用了这个：

<key>NSAppTransportSecurity</key>
<dict>
  <!--Include to allow all connections (DANGER)-->
  <key>NSAllowsArbitraryLoads</key>
  <true/>
</dict>

NSAppTransportSecurity
NSAllowsArbitraryLoads

---

然后在我的信息中设置这些值。plist

您是否尝试过设置

CG\u CONTEXT\u SHOW\u BACKTRACE

变量？我该怎么做？这也可能是一个bug。好的，谢谢。我报告了错误设置CG\u上下文\u显示\u回溯，转到编辑方案…>运行>参数>环境变量。添加值为1的变量CG_CONTEXT_SHOW_BACKTRACE。这与grapichs CONTEXT有什么关系？这并没有回答实际提出的问题，这是关于图形上下文，而不是传输安全性的问题