NSPredicate: problem solved (almost)

It only took me about four hours, but with big help from this post, I solved the problem of filtering a string containing an array of (possibly invalid) filepaths. And, in the meantime, Dave DeLong himself had responded to my question on StackOverflow from yesterday, which if I'd just waited a bit more, would have saved me some time. Thanks, Dave.

As I mentioned (here), we're just wrapping a filtering routine up in a category on NSString. Here is the first part of the code file including the category:

#import <Foundation/Foundation.h> @interface NSString (ValidatingFilepathArray) - (NSNumber *) validate; @end @implementation NSString (ValidatingFilepathArray) - (NSNumber *) validate { NSArray *A = [self componentsSeparatedByString:@":"]; NSString *s, *p; NSFileManager *fm = [NSFileManager defaultManager]; for (p in A) { s = [p stringByExpandingTildeInPath]; if ([fm fileExistsAtPath:s]) { NSLog(@"passed: %@", p); } else { NSLog(@"failed: %@", p); return [NSNumber numberWithBool:NO]; } } return [NSNumber numberWithBool:YES]; } @end

In the code at the bottom of the post, we construct a "function expression" from the new NSString method. Two things really confused me. First, in the method

expressionForFunction:selectorName:arguments:

the "function" is the object itself. And the second thing was figuring out the format string for the predicate that wraps up our expression:

@"FUNCTION(SELF, 'validate') isEqual:YES"

This is the output:

> gcc -o test test.m -framework Foundation > ./test 2011-03-13 16:53:42.974 test[3494:903] passed: ~ 2011-03-13 16:53:42.976 test[3494:903] passed: ~/Desktop 2011-03-13 16:53:42.977 test[3494:903] expression for ~:~/Desktop: YES 2011-03-13 16:53:42.978 test[3494:903] failed: xyz 2011-03-13 16:53:42.978 test[3494:903] expression for xyz: NO ------------------------------------------------- 2011-03-13 16:53:42.979 test[3494:903] passed: ~ 2011-03-13 16:53:42.980 test[3494:903] passed: ~/Desktop 2011-03-13 16:53:42.980 test[3494:903] failed: xyz 2011-03-13 16:53:42.981 test[3494:903] filtered: ~:~/Desktop 2011-03-13 16:53:42.981 test[3494:903] passed: ~/Desktop 2011-03-13 16:53:42.982 test[3494:903] evaluate: YES

First we construct the expression and evaluate it. In the second part, we construct the predicate and use it to filter an array or just "evaluate" a string. Still to do: test it in an app with bindings and an NSTextField or NSTableView.

Code:

int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; NSString *validPathArray = @"~:~/Desktop"; NSExpression *f = [NSExpression expressionForConstantValue:validPathArray]; NSExpression *e = [NSExpression expressionForFunction:f selectorName:@"validate" arguments:nil]; NSNumber *result = [e expressionValueWithObject:nil context:nil]; NSArray *responses = [NSArray arrayWithObjects:@"NO",@"YES",nil]; NSLog(@"expression for %@: %@", validPathArray, [responses objectAtIndex:[result intValue]]); NSString *invalidPathArray = @"xyz"; f = [NSExpression expressionForConstantValue:invalidPathArray]; e = [NSExpression expressionForFunction:f selectorName:@"validate" arguments:nil]; result = [e expressionValueWithObject:nil context:nil]; NSLog(@"expression for %@: %@", invalidPathArray, [responses objectAtIndex:[result intValue]]); printf("-------------------------------------------------\n"); NSPredicate *p; p = [NSPredicate predicateWithFormat:@"FUNCTION(SELF, 'validate') isEqual:YES"]; NSArray *A = [NSArray arrayWithObjects: validPathArray, invalidPathArray, nil]; NSArray *fA = [A filteredArrayUsingPredicate:p]; for (id obj in fA) { NSLog(@"filtered: %@", obj); } BOOL yesorno = [p evaluateWithObject:@"~/Desktop"]; NSLog(@"evaluate: %@", [responses objectAtIndex:(int) yesorno]); [pool drain]; return 0; }