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

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:

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