CODEWITHSUNDEEP
ios
Lochana Ragupathy
Lochana Ragupathy

Reputation: 4320

NSString on switch case

Instead of using else if like this

            if([screen isEqualToString :@"A"]){

               }
             else if(screen isEqualToString:@"B"){

               }

Will it work like this

          switch ([string isEqualToString:screen]){
          case ISA:
          break;

          case ISB:
          break;

          default:
          break;
       }

where ISA and ISB is defined like

       #define ISA [screen isEqualToString:A] and **will it be efficient**

Upvotes: 0

Views: 6598

Answers (2)

Tommy
Tommy

Reputation: 100662

The literal answer is, as per ATaylor and ACB, no. Switches require integers and at best you'd end up doing a pointer comparison, which isn't the same as isEqualToString:.

Options for cutting down the syntactic heft and processing cost of cascading if tests are dictionary based — you could in principle fill a dictionary with blocks keyed on strings but then for most practical purposes you'd need to create the dictionary rather too often so I tend to fill with selectors. E.g.

NSDictionary *stringsToSelectors =
    @{
          @"A" : [NSValue valueWithPointer:@selector(doTaskA)],
          @"B" : [NSValue valueWithPointer:@selector(doTaskA)],
    };

SEL selector = [[stringsToSelectors objectForKey:string] pointerValue];
[self performSelector:selector];

...

- (void)doTaskA
{
    // etc, etc
}

If you wanted to be even more naturally dynamic than that you could even go with:

NSString *selectorName = [NSString stringWithFormat:@"doTask%@", string];
SEL selector = NSSelectorFromString(selectorName);
if([self respondsToSelector:selector]) [self performSelector:selector];

...

- (void)doTaskA /* etc, etc */

Upvotes: 1

ATaylor
ATaylor

Reputation: 2598

No, I most certainly don't think so. switch/case is all about numeric if/then/else cases.

However what you COULD do is the following:

Write a function and pass it a variable number of arguments (since objective-c implements C look up va_args for the syntax). Pass it the original string and the strings you want to compare to.

Inside that function, use a 'for' loop, which compares the strings one by one until it either reaches the end or finds a match according to your criteria.

Once either is met, return the index. And that index you can use in switch case. A little example:

switch([self compareStrings:@"FirstString" Options:"@FirstString", @"SecondString"]) {
    case 0: //FirstString
    break;

    case 1: //SecondString
    break;

    default: //Not found
    break;
}

That should work. Regarding your function: Be sure to either incorporate an Optioncount, or make the options 'nil' terminated, because otherwise the function won't know when the end is actually reached.

Upvotes: 2

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