解决NSArray和NSDictionary中含有null时 writeToFile 失败的问题

由于dic中value有null，所以无法直接执行writeToFile，需要先进行归档才可以操作。

- (BOOL)storageAreasFileWith:(NSDictionary *)dict {

NSString *areasPath = [[NSFileManager documentsPath] stringByAppendingPathComponent:@"areas.plist"]；

NSData * data = [NSKeyedArchiver archivedDataWithRootObject:dict];

return [data writeToFile:areasPath atomically:YES];

}

- (NSArray *)outPutAreasDictionary {

NSString *areasPath = [[NSFileManager documentsPath] stringByAppendingPathComponent:@"areas.plist"]；

NSData * data = [NSData dataWithContentsOfFile:areasPath];

return  [NSKeyedUnarchiver unarchiveObjectWithData:data];

}