iOS best practices - check some conditions before running methods [closed] - ios

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I need some best pratices advice when checking conditions before running some methods.
Let's consider the following implementation :
#interface Foo : NSObject {
NSObject *_anObject;
}
#end
#implementation Foo
- (id)aMethod
{
if (!_anObject) return nil;
// do something
return obj;
}
- (id)aMethod2
{
if (!_anObject) return nil;
// do something
return obj;
}
Even if this implementation works well, I find pretty ugly to have these redundant checking codes if (!_anObject) return nil;.
So do you have some best pratices to avoid this ? (other than creating a macro to replace the line of code, which is pretty the same ugliness)
Thx in advance for your help.

Answer 1

Hmm, a few thoughts. I think it will depend a lot on what your // do something does.
If this is just a few methods, I think what you are doing is perfectly readable. And I agree a macro would only add confusing when reading the code.
Another thing to remember is in Objective-C you can call methods on a nil object safely, so maybe the check isn't necessary? Or you could try a null object-ish pattern. Usually used to prevent null pointer references which isn't a problem here, but maybe you could have a blank object that returns the correct thing if _anObject that makes sense in aMethod1 and aMethod2.
Another thought, if you are really checking for nil before all of your functions, perhaps you need to move up a level instead? It sounds like to me you have two classes. What about subclassing Foo with NilObjectFoo that just returns nil for all methods (or whatever)? Then when creating Foo, check if you have a _myObject and if you don't, create a NilObjectFoo instead. Then the rest of the code using that object doesn't care, and you are not cluttering up you Foo object with a bunch of nil checks.
Maybe a more concrete example would be helpful?

Answer 2

If I read you correctly (and I might not have), I would think that check of your belongs somewhere else. e. g.:
- (void)fooMethod{
if (_anObject){
// do whatever you need to do to the object, then:
NSObject *foo = [self aMethod];
}
}
- (id)aMethod{
// prepare the object you want
return obj;
}
This seems sturdier as you might need to have the result of aMethod used elsewhere even when _anObject is nil giving each fewer responsibilities. If you want a method to create several objects from different methods all depending on the state of _anObject you only need one outer if rather than the pattern you describe above:
- (void)fooMethod{
if (_anObject){
NSObject *foo = [self aMethod];
NSObject *bar = [self anotherMethod];
}
}