the final code in the filterContentForSearchText 

[self.filteredstaffList removeAllObjects]; // First clear the filtered array.

NSPredicate *predicate = nil;
if([scope isEqualToString:@"Staff Code"])
{
predicate = [NSPredicate predicateWithFormat:@"(SELF.staffCode contains[cd] %@)”, searchText]; 
}
if([scope isEqualToString:@"Staff FullName"])
{
predicate = [NSPredicate predicateWithFormat:@"(SELF.staffFullName contains[cd] %@)”, searchText]; 
}

NSArray *array = [staffList filteredArrayUsingPredicate:predicate];
self.filteredstaffList = [NSMutableArray arrayWithArray: array];

[product.productID compare:searchText options:NSCaseInsensitiveSearch];

What does that line do?

I also suggest that you consider modifying the predicate you are filtering with, rather than filtering using the if([scope isEqualToString...] bits. For example:

if([scope isEqualToString:@"Product ID"]) {
predicate = [NSPredicate predicateWithFormat:@"(SELF.productID contains[cd] %@)", searchText];
}

then the filtered array is just:

[tableData filteredArrayUsingPredicate:predicate]

so you won't need a loop.

You can even drop an AND or an OR into your predicate or just use NSCompoundPredicate's various class methods to make your filter more dynamic.

See Apple's Predicate Programming Guide for more details