summaryrefslogtreecommitdiffhomepage
diff options
context:
space:
mode:
authorNami-Doc <vendethiel@hotmail.fr>2013-12-31 13:17:06 -0800
committerNami-Doc <vendethiel@hotmail.fr>2013-12-31 13:17:06 -0800
commite4db90a2f9d56fdda3cc367cbd618dd719ce3f53 (patch)
treec0fc4e4acfcc6924f89d114da09a30f07a04de53
parent8bd91cb6e263e914ec4397f11e753bc4080c55ab (diff)
parent8e04611520cc385ccfd96ca1e8cfd8e30fc2ce40 (diff)
Merge pull request #471 from levibostian/objective-c-memory-management
Objective-C memory management.
-rw-r--r--objective-c.html.markdown47
1 files changed, 47 insertions, 0 deletions
diff --git a/objective-c.html.markdown b/objective-c.html.markdown
index 419c0475..406b2e92 100644
--- a/objective-c.html.markdown
+++ b/objective-c.html.markdown
@@ -146,6 +146,10 @@ int main (int argc, const char * argv[])
[mutableSet addObject:@"Hello"];
NSLog(@"%@", mutableSet); // prints => {(Hello)}
+ // Set object
+ NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil];
+ NSLog(@"%@", set); // prints => {(Hello, World)}
+
///////////////////////////////////////
// Operators
///////////////////////////////////////
@@ -373,6 +377,49 @@ 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).
+
+// Because memory management can be a pain, Xcode 4.2 and iOS 4 introduced Automatic Reference Counting (ARC).
+// ARC is a compiler feature that inserts retain, release, and autorelease automatically for you, so when using ARC,
+// you must not use retain, relase, or autorelease.
+MyClass *arcMyClass = [[MyClass alloc] init]; // Without ARC, you will need to call: [arcMyClass release] after
+// you're done using arcMyClass. But with ARC, there is no need. It will insert this release statement for you.
+
+// As for the "assign" and "retain" @property attributes, with ARC you use "weak" and "strong".
+@property (weak) MyClass *weakVar; // weak does not take ownership of object. If original instance's reference count
+// is set to zero, weakVar will automatically receive value of nil to avoid application crashing.
+@property (strong) MyClass *strongVar; // strong takes ownership of object. Ensures object will stay in memory to use.
+
+// For regular variables (not @property declared variables), use the following:
+__strong NSString *strongString; // Default. Variable is retained in memory until it leaves it's scope.
+__weak NSSet *weakSet; // Weak reference to existing object. When existing object is released, weakSet is set to nil.
+__unsafe_unretained NSArray *unsafeArray; // Like __weak but unsafeArray not set to nil when existing object is released.
```
## Further Reading