Checking to see if ObjectForKey exists [duplicate] - objective-c

Question

Most of the examples I found on the net write this:
if(x != nil)
// ...
Is there any problems with this?
if(x)
// ...
I tried both in a simple program and couldn't found any difference.

Answer 1

In Objective-C, nil is defined as a value called __DARWIN_NULL, which essentially evaluates to 0 or false in if-statements. Therefore, writing
if (x == nil) is the same as writing if (!x) and writing if (x != nil) is equal to if (x) (since comparing to false creates a negation, and comparing to true keeps the condition the same).
You can write your code either way, and it really depends on which you think is more readable. I find if (x) to make more sense, but it depends on your style.
It's like comparing if (someCondition == true) versus if (someCondition).
It all depends on you, and who's going to be reading the code.
Edit: As Yuji correctly mentions, since Objective-C is a superset of C, any condition that evaluates to a value other than 0 is considered to be true, and therefore, if someCondition in the example above were to evaluate to an integer value of, say, -1, comparing it to true would result in false, and the if-statement would not be evaluated. Something to be aware of.

Answer 2

Both
if (x != nil)
and
if ( x )
are equivalent, so pick the variant that in your opinion makes your code more readable for you (and others who will read and support your code)

Answer 3

Both are the same and this is a style question and it boils down to whether you prefer:
if (something) { ... }
versus
if (something != nothing) { ... }
I have always found #1 more clear but #2 is used extensively in documentation and hence the field so it is better to both know both forms and adapt to what a project uses and be stylistically consistent.

Answer 4

The best and safe way to check nil is
Make a common method, and add all these null :
+ (NSString *)trimWhiteSpaceAndNewLine:(NSString *)string {
NSString *stringSource = [NSString stringWithFormat:#"%#",string];
if ([stringSource isEqualToString:#"(null)"]) {
stringSource = #"";
return stringSource;
}
if ([stringSource isEqualToString:#"<null>"]) {
stringSource = #"";
return stringSource;
}
if ([stringSource isEqualToString:#"<nil>"]) {
stringSource = #"";
return stringSource;
}
if ([stringSource isKindOfClass:[NSNull class]]) {
stringSource = #"";
return stringSource;
}
if ([stringSource isEqualToString:#""]) {
stringSource = #"";
return stringSource;
}
if (stringSource == nil) {
stringSource = #"";
return stringSource;
}
NSString *stringFinal = [stringSource stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
return stringFinal;
}
And check
NSString *strUuid = [Common trimWhiteSpaceAndNewLine:[dict valueForKeyPath:#"detail.uuid"]];
if (![strUuid isEqualToString:#""]) {
// do your stuff
}