We’ve probably all seen the regular NSOpenPanel sample code from AppleComputer - it goes like this:

• (void)openDoc:(id)sender { int result; NSArray *fileTypes = [NSArray arrayWithObject:@”td”]; NSOpenPanel *oPanel = [NSOpenPanel openPanel];

  [oPanel setAllowsMultipleSelection:YES]; result = [oPanel runModalForDirectory:NSHomeDirectory() file:nil types:fileTypes]; if (result == NSOKButton) { NSArray *filesToOpen = [oPanel filenames]; int i, count = [filesToOpen count]; for (i=0; i<count; i++) { NSString *aFile = [filesToOpen objectAtIndex:i]; id currentDoc = [[ToDoDoc alloc] initWithFile:aFile]; } } }

This works only with filename extensions, however. Sometimes it might be desirable to display files that have a certain FileType instead of a filename extension.

To do that, simply change the line

NSArray *fileTypes = [NSArray arrayWithObject:@”td”];

in the above example to something like this:

NSArray* fileTypes = [NSArray arrayWithObjects:NSFileTypeForHFSTypeCode(‘TEXT’), nil];

(Based on a a mailing list post by Brant Vasilieff.)

Question: Does anyone know if the nil object in the last code line is really necessary?

Answer: yes.

You bet your ASCII. Read up on ‘arrayWithObjects’ in NSArray. This is a varargs style list of inputs:

• (id)arrayWithObjects:(id)firstObj, …;

The C spec basically requires variable-length parameter lists to declare their parameters explicitly (as in printf) or for lists to be null terminated. (Hmmm … it’s like the difference between pascal strings and c strings.) If you skip the nil your app will die a horrible death as it chews through your program’s address space looking for a nil word.

If you really hate nils just change ‘arrayWithObjects’ to ‘arrayWithObject’. arrayWithObject takes only one parameter. But ‘arrayWithObjects’ is easier to extend when you copy/paste it into your next project …

– MikeTrent