NSString to class instance variable

Question

I am looking for a way to convert from NSString to a class instance variable. For sample code below, say filter is "colorFilter". I want filternameclassinstancegohere to be replaced with colorFilter.

- (void)filterSelected:(NSString *)filter
{
    self.filternameclassinstancegohere = ….;
}

Does this class have a specific range of filters, and you are setting it by using a string? Have you looked at an enum instead? — jrturton, Nov 27 '11 at 18:27
Currently filter can be any of 40 NSString names. The reason why I am looking to do this way so I do have to use the switch statement. — user523234, Nov 27 '11 at 18:34
What is supposed to go after the =? i.e your ideal method is self.ColorFilter = _what_? — jrturton, Nov 28 '11 at 14:21
Oh! Now I see that, and re-look at your question, it all makes sense! Well done! — jrturton, Nov 29 '11 at 15:52

score 5 · Accepted Answer · answered Nov 29 '11 at 15:36

While there were good suggested solutions given for this question, I discovered what I needed is the NSClassFromString method. Here is a final implementation:

- (void)filterSelected:(NSString *)filter
{
    //self.filternameclassinstancegohere = ….;
    self.myViewController = [[NSClassFromString(filter) alloc] initWithNibName:filter bundle:nil];

}

score 4 · Answer 2 · answered Nov 27 '11 at 18:38

4

Consider using one NSMutableDictionary instance variable with string keys rather than 40 instance variables.

answered Nov 27 '11 at 18:38

Jakob Egger

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This is another good suggestion for another case. But in my case, it can't be applied. – user523234 Nov 28 '11 at 14:16
Key/Value coding like `[self setValue:@"SomeValue" forKey:filter]` might work. But this might cause security problems... – Jakob Egger Nov 28 '11 at 20:20

score 2 · Answer 3 · answered Nov 27 '11 at 18:43

2

You can create an arbitrary selector using NSSelectorFromString():

SEL methodName = NSSelectorFromString(filter);
[self performSelector:methodName];

This will call a method colorFilter in your example above.

Would be wise to check with respondsToSelector before calling, too.

answered Nov 27 '11 at 18:43

jrturton

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This is good suggestion for another case. But in my case, I can't apply it. – user523234 Nov 28 '11 at 14:15
If you could extend your question with exactly what it is you want to do, I'm sure we can get a solution for you :) – jrturton Nov 28 '11 at 14:22

score 1 · Answer 4 · answered Nov 27 '11 at 18:33

If the filter value can only be a small, constant number of things, just use an enumeration and a switch statement:

enum Filter
{
  ColorFilter,
  FooFilter,
  BarFilter
};

- (void)filterSelected:(Filter)filter
{
  switch(filter)
  {
  case ColorFilter:
    self.colorFilter = ...;
    break;
  case FooFilter:
    self.fooFilter = ...;
    break;
  case BarFilter:
    self.barFilter = ...;
    break;
  }
}

If the set of filter values is large and could change frequently, then you could also use Key-Value Coding. It's more complicated but more flexible.

Good idea. Unfortunately, as I just explained it to jrturton. I don't want to use the switch statement. — user523234, Nov 27 '11 at 18:36

NSString to class instance variable

4 Answers4