How retrieve an index of an NSArray using a NSPredicate?
Using NSPredicate you can get array of strings that contain your search string (it seems there's no built-in method to get just element indexes):
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF CONTAINS[cd] %@", searchString];
NSArray *filteredArray = [array filteredArrayUsingPredicate: predicate];
You can get only indexes using indexesOfObjectsPassingTest:
method:
NSIndexSet *indexes = [array indexesOfObjectsPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop){
NSString *s = (NSString*)obj;
NSRange range = [s rangeOfString: searchString];
return range.location != NSNotFound;
}];
If you want to get just one element containing your string you can use similar indexOfObjectPassingTest:
method for that.
You should be able to do this with blocks. Below is a snippet (I don't have a compiler handy so pls excuse any typos):
NSArray *array = [NSArray arrayWithObjects:
@"New-York City",
@"Washington DC",
@"Los Angeles",
@"Detroit",
nil];
NSString *matchCity = @"Los";
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF contains[cd] %@", matchCity];
NSUInteger index = [self.array indexOfObjectPassingTest:^(id obj, NSUInteger idx, BOOL *stop) {
return [predicate evaluateWithObject:obj];
}];
Essentially you can use the indexOfObjectPassingTest: method. This takes a block (code following the "^") and returns the index for the first object that matches your predicate (or NSNotFound if no match exists). The block iterates through each object in the array until either a match is found (at which point it returns the index) or no match is found (at which point it returns NSNotFound). Here is a link to block programming that can help you understand the logic within the block:
https://developer.apple.com/library/ios/featuredarticles/Short_Practical_Guide_Blocks/
Found an alternative approach helpful where the search is more complex as it allows predicate to be used to find object then object to find index:
-(NSIndexPath*) indexPathForSelectedCountry{
NSUInteger indexToCountry = 0;
NSPredicate * predicate = [NSPredicate predicateWithFormat:@"isoCode = %@",self.selectedCountry.isoCode];
NSArray * selectedObject = [self.countryList filteredArrayUsingPredicate:predicate];
if (selectedObject){
if (self.searchDisplayController.isActive){
indexToCountry = [self.searchResults indexOfObject:selectedObject[0]];
}else{
indexToCountry = [self.countryList indexOfObject:selectedObject[0]];
}
}
return [NSIndexPath indexPathForRow:indexToCountry inSection:0];
}