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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 |