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iOS Objective-C Basics (Retired) Introduction to Objective-C From Structs to Objects

Posted by Joseph Lau
Joseph Lau
5,420 Points

Objective-C: Dynamic Memory Allocation?

@7:30 of the video:

http://teamtreehouse.com/library/objectivec-basics/introduction-to-objectivec/from-structs-to-objects

1) He instantiates a "TYPE" Sphere called ball; is this what's called an "instance of a class" also known as "object"? Or is Sphere simply analogous to a data "TYPE" like int, float, and char? Or even perhaps it means both in which a "class" means "a data type which groups together other data types and methods", such as a "struct" in C?

2) Also, at the same time in the video, what does he mean when he says "we need to ALLOCATE it because it's using DYNAMIC MEMORY"? What does allocating an object even mean? Dynamic memory?

1 Answer

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

yes he creates a Sphere object named ball. Sphere is a class, which means that instances of that class are called objects. A Sphere is not a primitive type like int, float etc. It is an object.

From Wikipedia on Dynamic memory in objective-C:

^In Objective-C (unlike in C++), all objects are created dynamically. This means that they continue to exist until they are explicitly destroyed.

To create an object, send its class an alloc message: [aClass alloc];. Note that this returns a new instance of the class but does not initialize its data. Typically you want to immediately send the new object an init message to remedy this. Allocation and initialization are usually combined in one line:

aClass *newobj = [[aClass alloc] init];

http://en.wikibooks.org/wiki/Cocoa_Programming/Memory_management