Passing nil object pointer in Objective-C

Question

I create an object which I set to nil by default before including it in a method as a parameter. I do a check later if the object is still nil or not. The object is set to change in the method but the result is still nil. I'd expect the method to be able to alter the nil object. If I have the code that's inside the method replace the method call, it results in it being NOT nil.

MyObject *objectTemp = nil;

[self methodCallWithObject:objectTemp];

if  (objectTemp == nil) NSLog(@"nil");
else NSLog(@"NOT nil");

// always results in "nil"

method:

-(void) methodCallWithObject:(MyObject)objectTemp {

    objectTemp = [NSValue valueWithCGPoint:CGPointMake(5.3f, 2.6f)];

}

Duplicate of this one: stackoverflow.com/questions/11737505/… — uraimo
– uraimo, Commented Apr 16, 2015 at 20:57

mipadi · Accepted Answer · 2015-04-16 20:57:24Z

4

In order to change objectTemp outside of the method, you have to pass a pointer to objectTemp, which means that methodCallWithObject actually needs to take a pointer to a pointer:

-(void) methodCallWithObject:(MyObject **)objectTemp {
    *objectTemp = [NSValue valueWithCGPoint:CGPointMake(5.3f, 2.6f)];
}

(However, it would probably make more sense to have methodCallWithObject just return a new object.)

answered Apr 16, 2015 at 20:57

mipadi

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1 Comment

matt Over a year ago

What he said! Really the problem is understanding what pointers and objects are...

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