How to check if a directory exists in Objective-C

问题:

I guess this is a beginner's problem, but I was trying to check if a directory exists in my Documents folder on the iPhone. I read the documentation and came up with this code which unfortunately crashed with EXC_BAD_ACCESS in the BOOL fileExists line:

 -(void)checkIfDirectoryAlreadyExists:(NSString *)name {     NSFileManager *fileManager = [[NSFileManager alloc] init];      NSString *path = [[self documentsDirectory] stringByAppendingPathComponent:name];      BOOL fileExists = [fileManager fileExistsAtPath:path isDirectory:YES];      if (fileExists)     {         NSLog(@"Folder already exists...");     }  } 

I don't understand what I've done wrong? It looks all perfect to me and it certainly complies with the docs, not? Any revelations as to where I went wrong would be highly appreciated! Thanks.

UPDATED:

Still not working...

  -(void)checkIfDirectoryAlreadyExists:(NSString *)name {     NSFileManager *fileManager = [[NSFileManager alloc] init];      NSString *path = [[self documentsDirectory] stringByAppendingPathComponent:name];      BOOL isDir;     BOOL fileExists = [fileManager fileExistsAtPath:path isDirectory:&isDir];      if (fileExists)     {           if (isDir) {              NSLog(@"Folder already exists...");          }      }  } 

回答1:

Take a look in the documentation for this method signature:

- (BOOL)fileExistsAtPath:(NSString *)path isDirectory:(BOOL *)isDirectory 

You need a pointer to a BOOL var as argument, not a BOOL itself. NSFileManager will record if the file is a directory or not in that variable. For example:

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

回答2:

Just in case somebody needs a getter, that creates a folder in Documents, if it doesn't exist:

- (NSString *)folderPath {     if (! _folderPath) {         NSString *folderName = @"YourFolderName";         NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);         NSString *documentsDirectoryPath = [documentPaths objectAtIndex:0];         _folderPath = [documentsDirectoryPath stringByAppendingPathComponent:folderName];          // if folder doesn't exist, create it         NSError *error = nil;         NSFileManager *fileManager = [NSFileManager defaultManager];         BOOL isDir;         if (! [fileManager fileExistsAtPath:_folderPath isDirectory:&isDir]) {             BOOL success = [fileManager createDirectoryAtPath:_folderPath withIntermediateDirectories:NO attributes:nil error:&error];             if (!success || error) {                 NSLog(@"Error: %@", [error localizedDescription]);             }             NSAssert(success, @"Failed to create folder at path:%@", _folderPath);         }     }      return _folderPath; } 

回答3:

I have a Utility singleton class that I use for things like this. Since I can’t update my database if it remains in Documents, I copy my .sqlite files from Documents to /Library/Private Documents using this code. The first method finds the Library. The second creates the Private Documents folder if it doesn’t exist and returns the location as a string. The second method uses the same file manager method that @wzboson used.

+ (NSString *)applicationLibraryDirectory {              return [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject]; }   + (NSString *)applicationLibraryPrivateDocumentsDirectory {      NSError *error;     NSString *PrivateDocumentsDirectory = [[self applicationLibraryDirectory] stringByAppendingPathComponent:@"Private Documents"];      BOOL isDir;     if (! [[NSFileManager defaultManager] fileExistsAtPath:PrivateDocumentsDirectory isDirectory:&isDir]) {          if (![[NSFileManager defaultManager] createDirectoryAtPath:PrivateDocumentsDirectory                                        withIntermediateDirectories:NO                                                         attributes:nil                                                              error:&error]) {             NSLog(@"Create directory error: %@", error);         }     }      return PrivateDocumentsDirectory; } 

I use it like this in my persistent store coordinator initialization. The same principal applies to any files though.

NSString *libraryDirectory = [Utilities applicationLibraryPrivateDocumentsDirectory]; NSString *sourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:sqliteName]; NSString *destinationPath = [libraryDirectory stringByAppendingPathComponent:sqliteName]; 

文章来源: How to check if a directory exists in Objective-C