stringByReplacingOccurenceOfString fails - macos

Question

I'm trying to make a Mac OS X application that asks the user for a directory. I'm using an NSOpenPanel that gets triggered when the user presses a "Browse" button.
The problem is, [NSOpenPanel filenames] was deprecated, so now I'm using the URLs function. I want to parse out the stuff that's url related to just get a normal file path. So I tried fileName = [fileName stringByReplacingOccurrencesOfString:#"%%20" withString:#" "];, but that gave me an error:
-[NSURL stringByReplacingOccurrencesOfString:withString:]: unrecognized selector sent to instance 0x100521fa0
Here's the entire method:
- (void) browse:(id)sender
{
int i; // Loop counter.
// Create the File Open Dialog class.
NSOpenPanel* openDlg = [NSOpenPanel openPanel];
// Enable the selection of files in the dialog.
[openDlg setCanChooseFiles:NO];
// Enable the selection of directories in the dialog.
[openDlg setCanChooseDirectories:YES];
// Display the dialog. If the OK button was pressed,
// process the files.
if ( [openDlg runModal] == NSOKButton )
{
// Get an array containing the full filenames of all
// files and directories selected.
NSArray* files = [openDlg URLs];
// Loop through all the files and process them.
for( i = 0; i < [files count]; i++ )
{
NSString* fileName = (NSString*)[files objectAtIndex:i];
NSLog(#"%#", fileName);
// Do something with the filename.
fileName = [fileName stringByReplacingOccurrencesOfString:#"%%20" withString:#" "];
NSLog(#"%#", fileName);
NSLog(#"Foo");
[oldJarLocation setStringValue:fileName];
[self preparePopUpButton];
}
}
}
Interestingly enough, "Foo" never gets outputted to that console. It's like the method aborts at the stringByReplacigOccurencesOfString line.
If I remove that one line, the app will run and fill my text box with the string, just in URL form, which I don't want.

Answer 1

Your problem is that the NSArray returned by [NSOpenPanel URLs] contains NSURL objects, not NSString objects. You're doing the following cast:
NSString* fileName = (NSString*)[files objectAtIndex:i];
Since NSArray returns an id, there isn't any compile-time checking to make sure your cast makes sense, but you do get a runtime error when you try to send an NSString selector to what is actually an NSURL.
You could convert the NSURL objects to NSString and use your code mostly as-is, but there's no need for you to handle the URL decoding yourself. NSURL already has a method for retrieving the path portion which also undoes percent-encoding: path.
NSString *filePath = [yourUrl path];
Even if your code was dealing with just a percent-encoded NSString, theres stringByReplacingPercentEscapesUsingEncoding:.