archive失败

下面代码运行后SUCCESS为NO，请问什么原因？谢谢

    BOOL success=[NSKeyedArchiver archiveRootObject:object toFile:[Util.applicationDataDirectory URLByAppendingPathComponent:@"haha"].path];

//Util.m
    +(NSURL*)applicationDataDirectory
{
    NSFileManager* sharedFM = [NSFileManager defaultManager];
    NSArray* possibleURLs = [sharedFM URLsForDirectory:NSApplicationSupportDirectory                                             inDomains:NSUserDomainMask];
    NSURL* appSupportDir = nil;
    NSURL* appDirectory = nil;
    if ([possibleURLs count] >= 1) {
        // Use the first directory (if multiple are returned)
        appSupportDir = [possibleURLs objectAtIndex:0];
    }
    // If a valid app support directory exists, add the
    // app's bundle ID to it to specify the final directory.
    if (appSupportDir) {
        NSString* appBundleID = [[NSBundle mainBundle] bundleIdentifier];
        appDirectory = [appSupportDir URLByAppendingPathComponent:appBundleID];
    }
    return appDirectory;
}