Ios - Introduction to memory management

Ios - Introduction to memory management

• 1.
  1/82
• 2.
  2/82 Memory Management IniOS
• 3.
  3/82 Objective-C Memory management Memory managementis semi-automatic: The programmer must allocate memory for objects either a) explicitly (alloc) or b) indirectly using a convenience constructor No need to de-allocate
• 4.
  4/82 Allocation Allocation happens throughthe class method alloc. The message ‘alloc’ is sent to the class of the requested object. Alloc is inherited from NSObject. Every alloc creates a new instance (=object) [HelloWorld alloc]; The class creates the object with all zeros in it and returns a pointer to it. HelloWorld *p = [HelloWorld alloc]; The pointer p now points to the new instance. Now we send messages to the instance through p.
• 5.
  5/82 The reference counter •Every instance has a reference counter. It counts how many references are retaining the object. The counter is 1 after allocation. It does not count how many references exist to the object • Sending the retain message to the object increases the reference counter by 1. • Sending the release message decreases the reference counter by 1. • No need to do either if using ARC.
• 6.
  6/82 reference counter =retain counter • When the reference counter reaches zero, the object is automatically de-allocated. The programmer does not de-allocate. • The programmer only does: alloc retain release
• 7.
  7/82 Rules for memorymanagement • With no ARC: The method that does an alloc or a retain must also do a release, it must maintain the balance between: (alloc or retain) and (release) • If a method does alloc and returns a pointer to the created object then the method must do an autorelease instead of release.
• 8.
  8/82 Autorelease pool • Withno ARC: For outorelease to work the programmer must create an autorelease pool, using: NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; • When Cocoa is used then the autorelease pool is created automatically – the programmer does not need to do it. • To release the pool and all objects in it, do: [pool release];
• 9.
  9/82 Convenience Constructors • Thisis a class method that allocates and initializes an object. The programmer is neither doing alloc nor init. • Example: +(id)studentWithName :(NSString*)name AndGpa:(float)gpa { id newInst = [[self alloc]initStudent:name :gpa]; return [newInst autorelease]; }
• 10.
  10/82 Convenience Constructors • Essential:the method sends alloc to self which is the Student class object • Essential: the method autoreleases the instance, because it returns a pointer to the created instance • Not essential: This example uses an existing initializer, it could use something else or initialize the Student data directly
• 11.
  11/82 Convenience Constructors Calling theconvenience constructor: id stud = [Student studentWithName:@"Johnnie" AndGpa: 3.8]; The message is sent to the Student class object and returns a pointer to it, the pointer is assigned to stud The calling code does neither alloc nor init An autorelease pool must be in place
• 12.
  12/82 End of MemoryEndof Memory • With newer versions of Xcode, the memory management is becoming more and more automatic. • Use Automatic Reference Counting ARC to take advantage of the latest changes and improvements with memory management!
• 13.
  13/82 ThankThank You !!!You!!! For More Information click below link: Follow Us on: http://vibranttechnologies.co.in/ios-classes-in-mumbai.html