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iOS Objective-C Basics (Retired) Introduction to Objective-C Syntax Overview

Posted by bronnyreinhardt
bronnyreinhardt
1,007 Points

The particulars of syntax

I have a few questions after watching the syntax overview lesson.

First, the instructor notes that 'all of our instances are pointers' – so *ball. In main.m, why do you use star notation for the instance method in the first function call, but not in the second, or in the NSLog statement?:

int main()
{
    Sphere *ball = [[Sphere alloc] init];

    [ball setRadius:25];
    NSLog(@"ball radius %f", [ball radius]);

    return 0;
}

Second, the slide at the end provides the following breakdown of the Objective-C function-call syntax:

type foo = [classinstance instanceMethodwithParam1:param1 andParam2:param2];

which alludes to the second function call in main.m:

[ball setRadius:25];

So how does andParam2:param2]; figure into this code? Or does it not refer to the example from the lesson?

5 Answers

bronnyreinhardt
bronnyreinhardt
1,007 Points

Update: in case anyone else finds it useful, I got a really good answer for my pointers question here

Gregory Serfaty
Gregory Serfaty
37,140 Points
Gregory Serfaty
Gregory Serfaty
37,140 Points

Hi When you declare a pointer you need to do with a star * but after when you call you object you did not call it with the star

For the second question it is a example of method with 2 parameters but it is just a example. Your method could have 0 or more parameters.

A illite advise make this great tuto http://teamtreehouse.com/library/objectivec-basics

Sorry for my English ;)

I hope that help you

Good luck the next

bronnyreinhardt
bronnyreinhardt
1,007 Points
bronnyreinhardt
bronnyreinhardt
1,007 Points

Thanks for your response Gregory.

I suppose my question is, to clarify: all instances of an object are pointers. Why?

Patrick Serrano
Patrick Serrano
13,834 Points
Patrick Serrano
Patrick Serrano
13,834 Points

Because Objective-C is an extension of C, and C uses pointers. The pointers allows you to reference an object in more then one place without needing to allocate memory for each instance.

bronnyreinhardt
bronnyreinhardt
1,007 Points
bronnyreinhardt
bronnyreinhardt
1,007 Points

Thanks Patrick. So in this example, *ball is being declared as a pointer to the object Sphere? :)

Patrick Serrano
Patrick Serrano
13,834 Points
Patrick Serrano
Patrick Serrano
13,834 Points

Not exactly. The ball object is an instance of sphere, sphere is the class of the object.

The ball pointer points to the memory that is allocated for the ball object.

bronnyreinhardt
bronnyreinhardt
1,007 Points
bronnyreinhardt
bronnyreinhardt
1,007 Points

Right, so below an object is created that is an instance of Sphere. And an instance is always a pointer.

Sphere *ball = [[Sphere alloc] init];

You said, 'the ball pointer points to the memory that is allocated for the ball object.'

So an object and its pointer are being created at the same time?

I'm kind of having trouble digesting this (and it may be because I haven't fully wrapped my head around memory allocation in Objective-C).