Uploading Files to a Custom Object?

Question

iOS

Hello,
I use Quickblox. In the admin panel, in the Custom Object module, I created a table and added a field of the File type there. Then I try to save the file there and it doesn't work for me.
Tried like this:

[post.fields setObject:UIImagePNGRepresentation([UIImage imageNamed:@"profile"]) forKey:@"fileField"];

so

[post.fields setObject:[UIImage imageNamed:@"profile"] forKey:@"fileField"];

The result is the same. Nothing comes out.
Thank you!