Why can't I append a String to a NSURL?

Question

Appending the .txt file component to the URL path doesn't work:

var error:NSError?
let manager = NSFileManager.defaultManager()
let docURL = manager.URLForDirectory(.DocumentDirectory, inDomain:.UserDomainMask, appropriateForURL:nil, create:true, error:&error)
docURL.URLByAppendingPathComponent("/RicFile.txt") <-- doesn't work

via debugger:

file:///Users/Ric/Library/Developer/CoreSimulator/Devices/
<device id>/data/Containers/Data/Application/<app id>/Documents/

Writing a String using docURL to a file doesn't work because of the missing file name.

Reason (via error):

"The operation couldn’t be completed. Is a directory"

So Question: Why doesn't the following work?

docURL.URLByAppendingPathComponent("/RicFile.txt")

score 19 · Answer 1 · edited Aug 18 '14 at 21:29

19

URLByAppendingPathComponent: doesn't mutate the existing NSURL, it creates a new one. From the documentation:

URLByAppendingPathComponent: Returns a new URL made by appending a path component to the original URL.

You'll need to assign the return value of the method to something. For example:

let directoryURL = manager.URLForDirectory(.DocumentDirectory, inDomain:.UserDomainMask, appropriateForURL:nil, create:true, error:&error)
let docURL = directoryURL.URLByAppendingPathComponent("/RicFile.txt")

Even better would be to use NSURL(string:String, relativeTo:NSURL):

let docURL = NSURL(string:"RicFile.txt", relativeTo:directoryURL)

edited Aug 18 '14 at 21:29

David Berry

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answered Aug 18 '14 at 00:58

BergQuester

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1

`NSURL(string:String, relativeTo:NSURL)` will also work. It is even arguably more correct if your appended URL string may not be a relative path. as it will correctly deal with the stringUrl being interpreted relative to the base url instead of just appending it. – David Berry Aug 18 '14 at 07:22
Hmm, I overlooked that one. I'll update the question, thanks! – BergQuester Aug 18 '14 at 14:50
You're actually changing the url to be absolute (starting it with /) where the original question seems to be relative. I've edited your answer to be more inline with that. – David Berry Aug 18 '14 at 21:28

score 0 · Answer 2 · edited Aug 04 '16 at 14:46

With the update to the Swift language, the suggested call to manager.URLForDirectory(...) no longer works because the call can throw (an exception). The specific error is "Call can throw, but it is not marked with 'try' and the error is not handled". The throw can be handled with the following code:

    let directoryURL: NSURL?
    do
    {
        directoryURL = try manager.URLForDirectory(.DocumentationDirectory,
                            inDomain: .UserDomainMask, appropriateForURL: nil, create: true)
    }
    catch _
    {
        print("Error: call to manager.URLForDirectory(...) threw an exception")
    }

Why can't I append a String to a NSURL?

2 Answers2