iCloud:NSFileManager的startDownloadingUbiquitousItemAtURL的回调? [英] iCloud: Callback for NSFileManager's startDownloadingUbiquitousItemAtURL?

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问题描述

我正在使用 NSFileManager startDownloadingUbiquitousItemAtURL 将文件从iCloud下载到本地副本(本地还没有在这种情况下拥有该文件的副本)。我似乎找不到这个过程的回调。我需要回调告诉我的应用程序所请求的文件已完成下载(到本地副本),因此其他任务可以开始读取文件的内容并执行操作。

I am using NSFileManager's startDownloadingUbiquitousItemAtURL to download file from iCloud to local copy (the local does not yet have the copy of the file in this case). I can't seem to find the callback for this process. I need the callback to tell my app that the requested file is finished downloaded (to local copy) so other task can start reading the content of the file and does stuff.

我可以检查文件是否已下载。但它会不断涉及民意调查。有没有办法在没有设置计时器的情况下对此进行轮询?

I can check to see if the file is downloaded. But it would involve in polling constantly. Is there a way to do this without setting a timer to poll for this?

推荐答案

我相信这种方法的目的是与基于 Apple的文档。所以你需要像这样使用文件协调器:

I believe that this method is intended to be used in conjunction with file coordinators based on Apple's documentation. So you would need to use a file coordinator like so:

NSURL *itemURL = nil; // this is the URL you want to read from

__block NSData *data = nil;
NSError *error = nil;
NSFileCoordinator *coordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];
[coordinator coordinateReadingItemAtURL:itemURL options:0 error:&error byAccessor:^(NSURL *newURL) {
    data = [NSData dataWithContentsOfURL:newURL];
}];

然而,这将是同步的,所以如果你想异步做某事,你可以使用块作为所以:

This will be synchronous, however, so if you wanted to do something asynchronously, you could use blocks as so:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // read info from the URL using the code above
    dispatch_async(dispatch_get_main_queue(), ^{
        // handle data read from the URL
    });
});

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