小编wjh*_*wjh的帖子

我目前正在通过调用在后台线程中将一些文件写入磁盘

dispatch_async(my_queue,^{
   [self writeToRoot:filename data:data];
};

- (BOOL)writeToRoot:(NSString *)path data:(NSData *)content
{
    NSString *fullPath = [[self rootPath] stringByAppendingPathComponent:path];

    NSString *pathWithoutFile = [fullPath stringByDeletingLastPathComponent];

    BOOL directoryExists = [[NSFileManager defaultManager] fileExistsAtPath:pathWithoutFile];

    if (!directoryExists) {
        NSError *error = nil;
        [[NSFileManager defaultManager] createDirectoryAtPath:pathWithoutFile
                                  withIntermediateDirectories:YES
                                                   attributes:nil error:&error];
        NSParameterAssert(error == nil);
    }

    return [content writeToFile:fullPath atomically:NO];
}

我这样做,因为它不会阻止主线程.我的问题是如何确保线程安全.在执行此后台操作时,当我尝试通过调用从磁盘读取文件时会发生什么:

[NSData dataWithContentsOfFile:fullPath];

内容会被破坏吗？或者写操作会锁定文件,读操作会等到写完成吗？

我的相册里有一张gif图片.当我使用它UIImagePickerController来选择该图像时,我需要将图像转换NSData为存储.

早些时候,我用过

NSData *thumbData = UIImageJPEGRepresentation(thumbnail, 0.5);

但它不适用于gif图像.thumbData将是零.

1. 我如何NSData从gif图像中获取？

2. 我怎么知道它是一个需要特殊处理的gif图像？

我试图在用户选择图像后从UIImagePickerController推送视图控制器(用于额外编辑).
它被成功推动了.但是当弹出该视图控制器并且用户返回编辑屏幕时,编辑屏幕不再可交互.有谁知道这是什么问题.

    -(void)didTapBtn:(id)sender
        {
            self.picker = [[UIImagePickerController alloc] init];
            self.picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
            self.picker.delegate = self;
            self.picker.allowsEditing = YES;

            [self presentViewController:self.picker animated:YES completion:nil];
        }

        -(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
        {
            UIImage *image = [info objectForKey:UIImagePickerControllerEditedImage];

            if (image == nil) {
                image = [info objectForKey:UIImagePickerControllerOriginalImage];
            }

            if (image == nil) {
                return;
            }



           self.test = [[BTTestViewController alloc] init];
            self.test.delegate = self;

            [self.picker pushViewController:self.test animated:YES];
        }

//Called by BTTestViewController
        -(void)didCancel
        {
            [self.picker popViewControllerAnimated:YES];
        }