Why I get error when call method from controller?

Question

I create an object of class in current class:

 CustomTableViewController * dController = [[CustomTableViewController init] alloc];

[dController getItemsByCategory:@"3" andCategory:@"4"];

After this I get error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[CustomTableViewController<0x102b35298> init]: cannot init a class object.'

CustomTableViewController is:

    @implementation CustomTableViewController

    - (instancetype)init
    {
        self = [super init];
        if (self) {
            // TODO
        }

        return self;
    }

  - (void) getItemsByCategory: (NSString*) id andCategory:(NSString*)     category {

       // TODO
    }

    }

Also I have declared function getItemsByCategory in .h file

Answer 1

You're calling the methods in the wrong order here:

 CustomTableViewController * dController = [[CustomTableViewController init] alloc]

Change to

 CustomTableViewController * dController = [[CustomTableViewController alloc] init]

Answer 2

As already said, you're simply calling these methods in the wrong order.

However, I think it's worth knowing why what you're doing is fundamentally incorrect.

• [root@data-03] Executing task 'echoing' ['root@data-03'] current host: root@data-03 [root@data-01] Executing task 'echoing' ['root@data-03'] current host: root@data-01 Done. is a static method. It can only be called on a class, not an instance (alloc not CustomTableViewController). What it does is allocate the memory for your instance, and will return a new instance of your class.

• CustomTableViewController * is an instance method. It can only be called on an instance, not a class (init not CustomTableViewController *). What it does is initialise your instance, by performing basic setup, and will return that initialised instance.

Therefore, calling CustomTableViewController on a class makes absolutely no sense fundamentally, as there's no memory to perform the initial setup in to begin with.

It's the programming equivalent of trying to put objects in a box, before the box exists.