Testing If an object is nil or not - objective-c

Question

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
CGPoint location = [touch locationInNode:self];
SKNode *node = [self nodeAtPoint:location];
if ([node.name isEqualToString:#"play"]){
NSLog(#"play was touched");
SKScene *mainGameScene = [[MainGame alloc] initWithSize:self.size];
if (!mainGameScene){
SKTransition *transition = [SKTransition fadeWithColor:[UIColor blackColor] duration:0.5];
[self.view presentScene:mainGameScene transition:transition];
}
}
}
From my understanding the code above checks if mainGameScene is nil and if it is it then goes through the if statement.
Is this beneficial at all or is it just a waste of code because if the method that this code is in is called multiple times won't it create new objects of SKScene?

Answer 1

It is used to check if mainGameScene is initialized, because you can't presentScene if it is nil.
if you want only to check if object is initialized, then
SKScene *mainGameScene;
//creates new variable - place it at the beginning of the code, before #implementation and #interface
if(mainGameScene){
// it is already inited (you have already tapped once), it will be called always, since it is inited at else
//it is called when you tap the second, the third time, etcetera
SKTransition *transition = [SKTransition fadeWithColor:[UIColor blackColor] duration:0.5];
[self.view presentScene:mainGameScene transition:transition];
}else
{
//Calls only once, when you first touching the screen, and initing mainGameScene.
//It won't be called ANYMORE, since it is inited.
mainGameScene = [[MainGame alloc] initWithSize:self.size];
}
The code you have now is useless, as it is trying to do something with object, that isn't initialized.In my case, your mainGameScene won't be reinitialized, once it is inited.