Returning a list of directories with NSMetadataQuery and NSPredicate

问题

I'm trying to get a list of directories in the user's iCloud folder. I worked out how to look for special types of files (such as txt files) and it works fine:

NSMetadataQuery *query = [[NSMetadataQuery alloc] init];
_query = query;

//Search all files in the Documents directories of the application’s iCloud container directories:
[query setSearchScopes:[NSArray arrayWithObject:NSMetadataQueryUbiquitousDocumentsScope]]; 

NSPredicate *pred = [NSPredicate predicateWithFormat:@"%K ENDSWITH '.txt'", NSMetadataItemFSNameKey];

[query setPredicate:pred];
[query startQuery];

However, I'm now trying to get only directories. I've read through the docs concerning NSPredicate, but I have no clue how to go about looking for directories. I guess NSPredicate is not made for this? I can check if something is a directory like this:

    BOOL isDir;
BOOL exists = [fm fileExistsAtPath:path isDirectory:&isDir];
if (exists) {
    /* file exists */
    if (isDir) {
        /* file is a directory */
    }
 }

But how to apply this to a NSMetadataQuery, I have no clue. I'd be grateful for any help I can get.

EDIT:

I changed the predicate to [NSPredicate predicateWithFormat:@"%K.pathExtension = ''", NSMetadataItemFSNameKey];

I then determine when the query is finished like so:

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(queryDidFinishGathering:) name:NSMetadataQueryDidFinishGatheringNotification object:query];
[query startQuery];

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

NSMetadataQuery *query = [notification object];
[query disableUpdates]; // You should invoke this method before iterating over query results that could change due to live updates.
[query stopQuery]; // You would call this function to stop a query that is generating too many results to be useful but still want to access the available results.

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

}

And finally, I do a count, but this will always give me 0 however many directories I have in the cloud (I checked this via Lion and the Mobile Documents folder; e.g. I have Documents/myTXTs etc.). This is very strange. If I do a count on the text files, it will give me 4 as I have 4 txt files. So I guess my directories are not being counted:

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

    NSLog(@"Query count %i", [query resultCount]);

...

回答1:

I've tried EmptyStack's answer without luck....

I've found that NSMetadataQuery does NOT find directories, The problem is not the NSPredicate is filtering directories from the results, the problem is simply the query don't find folders. I've tried with the debugger and found that all LBItems found, are of regular files not directories. I hope Apple improves this in the future. ~~Maybe in MountainLion this is better since they seem to have folder support ... oops off course you didn't read this here because it's still NDA. Forget it~~

However there is at least one way of working-around this:

For example if your file structure is;

|_Folder
| |_file
| |_file2
|_Folder1
| |_file
|_file

and we make a query with predicate:

predicateWithFormat:@"%K LIKE '*'", NSMetadataItemFSNameKey

results will be (use NSMetadataItemURLKey to get the URL)

path/to/iCloud/Documents/Folder/file
path/to/iCloud/Documents/Folder/file2
path/to/iCloud/Documents/Folder1/file
path/to/iCloud/Documents/file

What we need to do is to filter these results by ourselves by looking at the number of components of each URL and chopping URLs as needed. Items at the first level should have numberOfComponentsOfUbiquitousContainer + 1, next level would have even one more and so on. We need to discard repetitions too (or like in this example we will get Folder twice).

Probably not optimal but works for me,

Update:

Better use below predicate, it reduce query results when crawling sub folders.

// dirPath is an NSString path of the directory you want
// to look at. Usually, for the top level directory:
// [NSFileManager URLForUbiquityContainerIdentifier:nil].path;
predicateWithFormat:@"%K BEGINSWITH %@", NSMetadataItemPathKey, dirPath];

回答2:

If you want to get only the directories use the following predicate.

predicateWithFormat:@"%K.pathExtension = ''", NSMetadataItemFSNameKey

Note that, this doesn't guarantee that you will get only the directories by using this method as there are (I've seen some) files which has no extensions. But if you are sure that all your files has extensions then you can very well use this.

If you want to get all the files regardless of their extension, just add the NOT keyword to the above predicate,

predicateWithFormat:@"NOT %K.pathExtension = ''", NSMetadataItemFSNameKey

回答3:

Try this:

[query setPredicate:[NSPredicate predicateWithFormat:@"%K like '*.txt'", NSMetadataItemFSNameKey]];

It works for me.

回答4:

You can do this with MDQuery - which is the 'real' code that NSMetadataquery uses.

In Terminal, type 'mdls' then drag in a folder. Then type mdfind and use the provided example only change the kMDItemContentType type tree to public.folder - you will get lots of results.

Then to do this in code, you need to follow an MDQueryRef example. The code flow is identical to the Cocoa stuff, and I find the queries much easier to create and understand. You can set cocoa callbacks to the MDQuery - so its pretty well drop in compatible with NSMetadataquery.

NSMetadataQuery has some iCloud stuff that I don't think is in MDQuery. So they are not identical, I think.

来源：https://stackoverflow.com/questions/7873974/returning-a-list-of-directories-with-nsmetadataquery-and-nspredicate

标签

iphone

objective-c

ios5

nspredicate

icloud