为什么人们倾向于将NSURL存储为NSString

Question

All over the internet as well as here on SO, I see code similar to this

NSString *imageUrl = [NSString stringWithFormat:@"%@",[info valueForKey:UIImagePickerControllerReferenceURL]];

and then

NSURL *url = [[NSURL alloc] initWithString:imageUrl];

Why not just store the NSURL? is it because of optimization? Is NSString that less expensive to store?

Answer 1

A lot of the time, it doesn't seem to be an issue of space (storing an NSString would be more efficient if the NSURL wouldn't contain any other specific data, but not to the point of making a difference in most applications).

Really, the most common reason for storing a URL as string is that it's the way we think of URLs ourselves—simply strings.

In the end, the most applicable/specific choice is generally best— NSURL represents "a URL that can potentially contain the location of a resource on a remote server, the path of a local file on disk, or even an arbitrary piece of encoded data" ( source ), while an NSString simply represents a string of text—if a URL is what you're going for, use NSURL .

(One clear upside to NSString 's is that they're more portable—but NSURL can be serialized and moved about if needed, too!).

Answer 2

NSString is more universally used. For example, AFNetworking uses strings instead of NSURLs. Also, if you need to send this URL to a web server as a parameter you will need it in string format as well.

Lazy instantiation is just a good practice in Obj-C. Create the objects only when you need them.