From dff26a28afbdc138cd21154e733839f52afaaab9 Mon Sep 17 00:00:00 2001 From: Levi Bostian Date: Tue, 31 Dec 2013 13:50:37 -0600 Subject: [PATCH] Add memory management examples. --- objective-c.html.markdown | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/objective-c.html.markdown b/objective-c.html.markdown index 98019404..9a11ebc8 100644 --- a/objective-c.html.markdown +++ b/objective-c.html.markdown @@ -377,6 +377,34 @@ NSLog(@"%i", myClass.count); // prints => 45 @end +/////////////////////////////////////// +// Memory Management +/////////////////////////////////////// +/* +For each object used in an application, memory must be allocated for that object. When the application +is done using that object, memory must be deallocated to ensure application efficiency. +Objective-C does not use garbage collection and instead uses reference counting. As long as +there is at least one reference to an object (also called "owning" an object), then the object +will be available to use (known as "ownership"). + +When an instance owns an object, its reference counter is increments by one. When the +object is released, the reference counter decrements by one. When reference count is zero, +the object is removed from memory. + +With all object interactions, follow the pattern of: +(1) create the object, (2) use the object, (3) then free the object from memory. +*/ + +MyClass *classVar = [MyClass alloc]; // alloc sets classVar's reference count to one. Returns pointer to object. +[classVar release]; // Decrements classVar's reference count. +// retain claims ownership of existing object instance and increments reference count. Returns pointer to object. +MyClass *newVar = [classVar retain]; // If classVar is released, object is still in memory because newVar is owner. +[classVar autorelease]; // Removes ownership of object at end of @autoreleasepool block. Returns pointer to object. + +// @property can use retain or assign as well for small convenient definitions. +@property (retain) MyClass *instance; // Release old value and retain a new one (strong reference). +@property (assign) NSSet *set; // Pointer to new value without retaining/releasing old (weak reference). + ``` ## Further Reading