App gets gets crash on release on array object in xcode - iphone

Question

I am facing strange issue, which is very common and may float at many sites, but this is bit strange. I am allocating mutable array object use object and then release as i did and doing every time of allocating and releasing object. It works fine when i comment release line and just use nil. Below is my code please see and suggest me better way.
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
NSMutableArray * array = [[NSMutableArray alloc] init];
array= [[dbSingleton sharedInstance] getAll_Players];
NSMutableDictionary * dict = [array objectAtIndex:row];
NSString * autoID = [dict objectForKey:#"autoId"];
NSLog(#"%#",[NSString stringWithFormat:#"%# %#",[dict valueForKey:#"fName"],[dict valueForKey:#"lName"]]);
[array release];
}
Please do not decrease my point because this is very common and people can't like these question to b ask. Thanks in advance.

Answer 1

No need to alloc-init and release your array.
I guess you do not require a new array with the same content, whereas only reference of your sharedInstance array is required.
For that, remove those lines and only decalre your array:
NSMutableArray *array = [[dbSingleton sharedInstance] getAll_Players];
As you have not alloc-init any array here, no need to release the same. Hence, no memory concerns required.
For the max, to reduce reference count what you can do is, immediately when its done with the reference, nullify that one:
NSMutableArray * array= [[dbSingleton sharedInstance] getAll_Players];
NSMutableDictionary * dict = [array objectAtIndex:row];
NSString * autoID = [dict objectForKey:#"autoId"];
NSLog(#"%#",[NSString stringWithFormat:#"%# %#",[dict valueForKey:#"fName"],[dict valueForKey:#"lName"]]);
array = nil; // not mandatory, it will work without this line as well
This methodology will work for both, ARC or Non-ARC.
Hope this helps.

Answer 2

First you initialize the array variable
NSMutableArray * array = [[NSMutableArray alloc] init];
And correctly at this point, you should release this variable at some point.
But, when you write
array= [[dbSingleton sharedInstance] getAll_Players];
You overwrite the array variable you just allocated, and array is now not something you should release here, unless you also call retain on the array you get from getAll_Players.
To fix the issue you should do it like this:
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
NSMutableArray * array = [[dbSingleton sharedInstance] getAll_Players];
NSMutableDictionary * dict = [array objectAtIndex:row];
NSString * autoID = [dict objectForKey:#"autoId"];
NSLog(#"%#",[NSString stringWithFormat:#"%# %#",[dict valueForKey:#"fName"],[dict valueForKey:#"lName"]]);
}
EDIT: (As answer to the question in the comment)
NSMutableArray * array = [[dbSingleton sharedInstance] getAll_Players];
The above line simply sets the variable 'array' as a pointer to whatever '[[dbSingleton sharedInstance] getAll_Players]' returns. The reference count is not increased nor decreased in that line, and you should therefore not decrease it either. (And NEVER trust the retain count value of any object, as objects are not always released when you expect them too).
The reference count is only increased when calling alloc, new, copy and mutableCopy when creating an object and calling retain on and object, and only when you yourself have used these keywords, should you ever release or autorelease an object. Note that this keywords increase the RF count. Where release and autorelease decrease the RF count.
It is expected objective-c practice to make sure that any function that returns an object, returns an object with the retain count of 0, unless the function name has one of the above keywords in its name. (and you should of course call 'autorelease' and not 'release' on the object before returning it)
When you use one of those keywords, the receiver should expect an rf count of 1, and that the receiver will make sure to release the object when he or she is done with it.
This is also what you should expect from any built-in functions.
That is why you should not release the object 'array' from the above line.