objective-c - NSMetadataQuery 找不到 iCloud 文件

Question

我按照 Apple Docs NSMetadataQuery 中的描述使用它来搜索我的 iCloud 文件。我只有一个文件，而且我知道它的名字。我的问题是有时这个文件不存在(我猜是因为它还没有被下载)并且 NSMetadataQuery 无法找到它。

曾经尝试使用 NSFileManager startDownloadingUbiquitousItemAtURL:error: 强制下载，但它返回了一个错误。 (阅读编辑)

我的解决方案是，我第一次创建文件，然后我猜它存在，然后用 UIDocument 打开它。但它可能不存在，或者它可能是用户第一次打开应用程序。我不能确定这些事情。我的第一个问题是:如果 UIDocument 打开文件，则意味着它在某处找到了文件。如果文件不存在，它如何使用该文件？

然后，第二个问题:如果我的应用程序必须管理多个文件或名称未知的文件。如果 NSMetadataQuery 不起作用，我如何找到它们。

编辑:如果应该使用 startDownloadingUbiquitousItemAtURL 开始下载文件，我如何知道文件何时完成下载(可能带有通知)？但是，更重要的是:如果总是说(删除原始名称)，我该如何下载文件？

   Error Domain=NSPOSIXErrorDomain Code=2 "The operation couldn’t be completed.
    No such file or directory" UserInfo=0x166cb0 {
    NSDescription=Unable to get real path for Path
'/private/var/mobile/Library/Mobile Documents/teamid~com~team~app/Documents/file.extension'
    }

Answer 1

我建议对 iCloud 文件执行以下加载例程。它包括 4 个步骤:

1. 首先，测试是否可以访问 iCloud
2. 然后查找您的文件(查找您指定的特定文件或查找具有特定扩展名(如 *.txt)的所有文件，或者如果您真的不知道您要查找的文件扩展名，例如 NSPredicate *pred = [NSPredicate predicateWithFormat:@"NOT %K.pathExtension = '.'", NSMetadataItemFSNameKey]; 将返回所有具有扩展名的文件，如 jpg、txt、dat 等)<
3. 然后检查查询是否完成，并且
4. 最后尝试加载文件。如果该文件不存在，请创建它。如果确实存在，则加载它。

下面是这四个步骤的示例代码:

    - (void)loadData:(NSMetadataQuery *)query {

    // (4) iCloud: the heart of the load mechanism: if texts was found, open it and put it into _document; if not create it an then put it into _document

    if ([query resultCount] == 1) {
        // found the file in iCloud
        NSMetadataItem *item = [query resultAtIndex:0];
        NSURL *url = [item valueForAttribute:NSMetadataItemURLKey];

        MyTextDocument *doc = [[MyTextDocument alloc] initWithFileURL:url];
        //_document = doc;
        doc.delegate = self.viewController;
        self.viewController.document = doc;

        [doc openWithCompletionHandler:^(BOOL success) {
            if (success) {
                NSLog(@"AppDelegate: existing document opened from iCloud");
            } else {
                NSLog(@"AppDelegate: existing document failed to open from iCloud");
            }
        }];
    } else {
        // Nothing in iCloud: create a container for file and give it URL
        NSLog(@"AppDelegate: ocument not found in iCloud.");

        NSURL *ubiq = [[NSFileManager defaultManager] URLForUbiquityContainerIdentifier:nil];
        NSURL *ubiquitousPackage = [[ubiq URLByAppendingPathComponent:@"Documents"] URLByAppendingPathComponent:@"text.txt"];

        MyTextDocument *doc = [[MyTextDocument alloc] initWithFileURL:ubiquitousPackage];
        //_document = doc;
        doc.delegate = self.viewController;
        self.viewController.document = doc;

        [doc saveToURL:[doc fileURL] forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            NSLog(@"AppDelegate: new document save to iCloud");
            [doc openWithCompletionHandler:^(BOOL success) {
                NSLog(@"AppDelegate: new document opened from iCloud");
            }];
        }];
    }
}

- (void)queryDidFinishGathering:(NSNotification *)notification {

    // (3) if Query is finished, this will send the result (i.e. either it found our text.dat or it didn't) to the next function

    NSMetadataQuery *query = [notification object];
    [query disableUpdates];
    [query stopQuery];

    [self loadData:query];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:NSMetadataQueryDidFinishGatheringNotification object:query];
    _query = nil; // we're done with it
}

-(void)loadDocument {

    // (2) iCloud query: Looks if there exists a file called text.txt in the cloud

    NSMetadataQuery *query = [[NSMetadataQuery alloc] init];
    _query = query;
    //SCOPE
    [query setSearchScopes:[NSArray arrayWithObject:NSMetadataQueryUbiquitousDocumentsScope]];
    //PREDICATE
    NSPredicate *pred = [NSPredicate predicateWithFormat: @"%K == %@", NSMetadataItemFSNameKey, @"text.txt"];
    [query setPredicate:pred];
    //FINISHED?
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(queryDidFinishGathering:) name:NSMetadataQueryDidFinishGatheringNotification object:query];
    [query startQuery];

}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    NSLog(@"AppDelegate: app did finish launching");
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];

    // Override point for customization after application launch.
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil] autorelease];
    } else {
        self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController_iPad" bundle:nil] autorelease];
    }

    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    // (1) iCloud: init

    NSURL *ubiq = [[NSFileManager defaultManager] URLForUbiquityContainerIdentifier:nil];
    if (ubiq) {
        NSLog(@"AppDelegate: iCloud access!");
        [self loadDocument];
    } else {
        NSLog(@"AppDelegate: No iCloud access (either you are using simulator or, if you are on your phone, you should check settings");
    }


    return YES;
}