Question

I’m just starting out in Objective-C, and have created an iOS program that I’d like to improve upon. In it, I’ve got two code blocks:

if ([stringTest isEqualToString:@"apple"]){
    numTest=0;
}else if (([stringTest isEqualToString:@"orange"])||([stringTest isEqualToString:@"lemon"])){
    numTest=1;
}else if ([stringTest isEqualToString:@"pumpkin"]){
    numTest=2;   // and so on...

And then the reverse:

  if (numTest==0){
        stringTest=@"apple";
    } else if (numTest==1){
        stringTest=@"orange/lemon";
    } else if (numTest==2){
        stringTest=@"pumpkin";  // and so on...

As these lists actually involve many more items, I’m sure there’s a much better way to do this. Any suggestions would be very much appreciated. Thanks for reading.

Answer 1

I would suggest setting up NSDictionaries that map the strings to numbers and numbers to strings. With the new object literal syntax:

NSDictionary* numberLookup = @{@"apple": @0, @"orange", @1, @"lemon", @2, @"pumpkin": @3};
numTest = [numberLookup objectForKey:stringTest];

NSDictionary* stringLookup = @{@0, @"apple", @1, "orange/lemon", .....
stringTest = [stringLookup objectForKey:numTest];

The literal syntax for NSDictionary is @{key: value, ...}. Note the use of @ symbols preceeding the numeric values; NSDictionary expects all keys and values to be objects. @1 is equivalent to [NSNumber numberWithInt:1]. And The dictionary literal syntax is similar to [NSDictionary dictionaryWithObjectsAndKeys:@0, @"apple", ..., nil].

Edit: generating the second dictionary from the first

// Map strings to numbers
NSDictionary* numberLookup = @{@"apple": @0, ...};

// Map numbers to strings
NSMutableDictionary* stringLookup = [NSMutableDictionary dictionaryWithCapacity:numberLookup.count];
for (str in numberLookup) {
    id num = [numberLookup objectForKey:str];
    if ([stringLookup objectForKey:num]) {
        NSString* currentStr = [stringLookup objectForKey:num];
        [stringLookup setObject:[NSString stringWithFormat:@"%@/%@", currentStr, str] forKey:num]
    } else {
        [stringLookup setObject:str forKey:num];
    }
}