How to release memory for declared object in iPhone [duplicate] - iphone

Question

This question already has answers here:
app crash in the dealloc
(2 answers)
Closed 9 years ago.
I'm facing small problem,
I declare an array in .h file and allocate it in viewDodLoad method. In dealloc method I check if array not equal to nil then array=nil. But it's crashing in iOS 5.1.1. I can't understand reason for this crash.
My code,
#interface SampleApp : UIViewController
{
NSMutableArray *objArray;
}
#end
#implementation SampleApp
- (void)viewDidLoad
{
[super viewDidLoad];
objArray=[[NSMutableArray alloc]init];
}
-(void)dealloc
{
[super dealloc];
if (objArray!=nil)
{
[objArray removeAllObjects];
[objArray release];objArray=nil;
}
}

Answer 1

Add [super dealloc]; at the end of dealloc method and not at beginning. It is recommended by Apple in its documentation for dealloc method.
When not using ARC, your implementation of dealloc must invoke the superclass’s implementation as its last instruction.
Modify your code as below,
-(void)dealloc
{
if (objArray!=nil)
{
[objArray removeAllObjects];
[objArray release];objArray=nil;
}
[super dealloc];
}
Also, you need not call [objArray removeAllObjects] when you are releasing the entire array. When array is released, internally it will call release on all contained objects.
Hope that helps!

Answer 2

[super dealloc] method must be call in end of this method. Because you can not access variables of the superclass anymore because they are released when you call [super dealloc]. It is always safe to call the superclass in the last line.
-(void)dealloc
{
// ----------- your stuff ------------
[super dealloc];
}

Answer 3

With manual memory management, your -dealloc method looks as follows:
-(void)dealloc
{
[objArray release]; // objArray *may* be nil, and this is
// sufficient to release all elements as well.
// call super at the end
[super dealloc];
}
Additionally, you have a potential memory leak in your method -viewDidLoad. If you do it like your example:
- (void)viewDidLoad
{
[super viewDidLoad];
objArray=[[NSMutableArray alloc]init];
}
you may assign objArray a new pointer even if objArray already holds a valid object. The new pointer value will simply override the old, and thus you cannot release the old anymore.
One way is to check whether objArray is not nil and then release it before assigning it a new value:
- (void)viewDidLoad
{
[super viewDidLoad];
if (objArray) {
[objArray release], objArray = nil;
}
objArray = [[NSMutableArray alloc]init];
}
The better approach however is to employ "lazy initializing properties":
First, define an "internal property" for your array (unless you want the array publicly accessible). In your .m file:
// In your implementation file define a private property in a class extension:
#interface SampleApp ()
#property (nonatomic) NSMutableArray* objArray;
#end
#implementation SampleApp
#synthesize objArray = _objArray; // this will create the setter
-(void)dealloc
{
[_objArray release];
[super dealloc];
}
// Lazy init property: (this is the getter)
- (NSMutableArray*) objArray {
if (_objArray == nil) {
_objArray = [[NSMutableArray alloc] init];
}
return _objArray;
}
- (void) viewDidLoad {
[super viewDidLoad];
// When needing the array, simply *and always* access it
// through the property "self.objArray":
NSUInteger count = [self.objArray count];
}
...
Lazy initialization of properties are quite handy. Basically, you won't worry anymore if they are initialized or not - they simply are, when you use the property accessor.