[__NSArrayM getFileSystemRepresentation：maxLength：]：发送到实例的无法识别的选择器

Question

I have the following code to load some files and save them to disk:

NSDictionary *dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:[NSData dataWithContentsOfURL:url]];
// THE LINE BELOW IS WHERE THE EXCEPTION OCCURS
NSMutableArray *paths = [[NSMutableArray alloc] initWithArray:[NSKeyedUnarchiver unarchiveObjectWithFile:[dictionary objectForKey:@"paths"]]];

if(dictionary)
{

    dispatch_async(dispatch_get_main_queue(), ^{

    NSLog(@"DOWNLOADED PATHS: %@", paths);

    NSFileManager *filemgr;
    NSString *docsDir;
    NSArray *dirPaths;

    filemgr = [NSFileManager defaultManager];

    dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    docsDir = [dirPaths objectAtIndex:0];

    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    for(NSObject *obj in paths)
    {

        NSString *identification = [defaults objectForKey:@"LatestID"];

        NSString *pageno = [NSString stringWithFormat:@"%i", [paths indexOfObject:obj]];
        NSString *name = [NSString stringWithFormat:@"%@paths%@.archive", identification, pageno];

        NSString *dataFilePath = [[NSString alloc] initWithString: [docsDir
                                                                    stringByAppendingPathComponent:name]];

        [NSKeyedArchiver archiveRootObject:paths toFile:dataFilePath];

    }

    });

}

However, when I run this code, the following exception appears:

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM getFileSystemRepresentation:maxLength:]: unrecognized selector sent to instance 0xc8809e0' * First throw call stack: (0x3623012 0x3448e7e 0x36ae4bd 0x3612bbc 0x361294e 0x2e2d7b4 0x2e2d762 0x2e5bc85 0x2e83c7a 0x8d98 0x406053f 0x4072014 0x40632e8 0x4063450 0x95336e12 0x9531ecca) libc++abi.dylib: terminate called throwing an exception (lldb)

Why is this happening?

Answer 1

It seems that [dictionary objectForKey:@"paths"] on the suspicious line contains an NSMutableArray instead of an NSString . Perhaps you meant [[dictionary objectForKey:@"paths"] objectAtIndex:0] instead.