Objective C: A cleaner way to check if a string isn't empty before creating and assigning a string to a dictionary key?

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I am creating an NSMutableDictionary and assigning an NSString (test and test1) to a parameter key.

  NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];

  if (test.length) {
      dictionary[@"test"] = test;
  }

  if (test1.length) {
      dictionary[@"test1"] = test1;
  }

This method does work. However, I am going to eventually have more strings and don't want a bunch of if statements. I don't want the dictionary keys to exist if the string is empty or nil.

Not sure if there is a way around this.

I thought about creating a separate function that accepts an array of key string and array of string values and use a for loop to see if string value is empty. Then, return a dictionary once the for loop ends. However, you can't insert nil into an NSArray

Something like this

- (void)updateDic:(NSMutableDictionary *)dic withString:(NSString *)str {
    if (!str || [str isEqualToString:@""]) {
        return;
    }

    dic[str] = str;
}

And then just iterate over all strings and use that method.

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What I'd do is create a NSMutableDictionary category, something like this:

NSMutableDictionary+CustomMethods.m:

- (void)setStringIfNotNil:(NSString *)string forKey:(id <NSCopying>)key {
    if (!string || !string.length) { return; }
    self[key] = string;
}

Then you can use it like this:

NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init];
[dictionary setStringIfNotNil:test forKey:@"test"]
[dictionary setStringIfNotNil:test1 forKey:@"test1"]

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There are three ways according to me.. The first one use the category in which you have to write if condition only single time and you can use it in any class of your project.

Second one by making a separate method to do that task(to check string nil or not and adding into the dictionary).

And the third one , just add all in an array and and perform the action in a loop.

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The syntax:

dictionary[@"test"] = test

will remove the value from the dictionary if test is nil (it's a difference between the normal -setObject:forKey: method and the -setObject:forKeyedSubcript: which that syntax invokes). However, that will not work for empty strings.

As mentioned in another answer, you could make an NSDictionary category method to check, then call that method instead.

You could also just use the regular dictionary[key] = value syntax, then when you are done, do:

[dictionary removeObjectsForKeys:[dictionary allKeysForObject:@""]];

If it's possible to have the keys repeated, and you don't want an empty string overriding an earlier valid valid, you would have to check each time -- either by the category method, or using a local macro or inline function or local method.

static inline void SetValidVal(NSMutableDictionary *dictionary, NSString *key, NSString *val) {
    if (val.length) { dictionary[key] = val; }
}

or

#define MY_SET_VALID_VAL(dictionary, key, val) if ((val).length) dictionary[key] = (val)

If the key names need to be the same as the name of the local variable, you can play other games with macros (this also assumes the local variable name "dictionary":

#define MY_UPDATE_VAL(val) if (val.length) dictionary[@#val] = (val)

Then MY_UPDATE_VAL(test1); would expand to:

if (test1.length) dictionary[@"test1"] = test1;

That's a bit magic though and probably not recommended.

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Comments
  • How your strings are looks like? Is it array?
  • I've thought about this too, but seems strange I have to keep sending the dictionary over and over. However, this might be the best way.
  • You send reference not all the dictionary. So it is safe to do like this.
  • Okay sounds good. I rewarded you the answer. Also, shouldn't I check length instead? It seems to be working, however after checking stackoverflow it seems people recommended your way.
  • if (str.length > 0) is a bit simpler to write and subjectively easier to read. Anyway, assigning nil to dictionary is ignored.