如何获取目录os x中的文件列表？

Question

I'm developing an application in Objective-C. The user selects a directory (using NSOpenPanel ) and then in the application displays a list of the files in this directory. This is working without a problem.

However, if the application is open anew and without selecting a directory through NSOpenPanel , just want to get a list of files in the selected directory in the past startup error occurs

NSCocoaErrorDomain Code = 257.

I suspect that if the user selects the directory manually via NSOpenPanel , the system somehow remembers it and give read access to this directory and getting her files (using the method contentsOfDirectoryAtPath ), and if the user does not select via NSOpenPanel directory and tries to get a list of its files error is generated access.

How can that be in this case?

Answer 1

If your app is sandboxed and you want to have access to files/directories between runs, then you need to store a security-scoped bookmark to the directory, rather than the directory itself.

This means that you need to add the boolean property com.apple.security.files.bookmarks.app-scope set to YES to the entitlements of the application, as well as com.apple.security.files.user-selected.read-write to allow file selection.

When you select the directory, you need to make a bookmark to it:

NSOpenPanel *panel = [[NSOpenPanel alloc] init];
panel.canChooseDirectories = YES;
NSInteger ret = [panel runModal];
if (ret == NSFileHandlingPanelOKButton) {
    NSURL *anUrl = [[panel URLs] lastObject];
    NSError *err;
    NSData *data = [anUrl bookmarkDataWithOptions:NSURLBookmarkCreationWithSecurityScope
                   includingResourceValuesForKeys:nil
                                    relativeToURL:nil
                                            error:&err];
    if (!data) {
        NSLog(@"%@", err);
        return NO;
    }

Now that you've got the bookmark, you need to persist it eg by doing:

    NSUserDefaults *def = [NSUserDefaults standardUserDefaults];
    [def setObject:data forKey:@"bookmark"];
    [def synchronize];

On restart of the application, you need to convert the bookmark from NSData back into an URL, this is done by doing:

BOOL stale = NO;
NSError *anError;
NSURL *url = [NSURL URLByResolvingBookmarkData:data
                                       options:NSURLBookmarkResolutionWithSecurityScope
                                 relativeToURL:nil
                           bookmarkDataIsStale:&stale
                                         error:&anError];
if (url && !stale) {
    [anURL startAccessingSecurityScopedResource];
    // Do something with URL
    [anURL stopAccessingSecurityScopedResource];
} else if (anError) {
    NSLog(@"%@", anError);
    return NO;
}

and if you had used the defaults persistence of the bookmark data, you would use:

NSUserDefaults *def = [NSUserDefaults standardUserDefaults];
NSData *data = [def objectForKey:@"bookmark"];

to restore the bookmark data from the userdefaults.