iOS problems viewing contents of array

blue-lion · May 17, 2012

hello again, i am experimenting with the addobject method ,and previously i have managed to interrogate the contains of the nsmutablearray within the debugger, but this time although no error or warning message is being displayed i can't seem to do it. The array variable is there, but shows no contents?

the array is declared as part of a class in the usual way

with

Code:

NSMutableArray *scoreLog;

@property(nonatomic,strong) NSMutableArray *scoreLog;

in the header

and in the implementation file

@synthesize scoreLog;

later in the implementation file , i have the following line

Code:

[scoreLog addObject:[NSNumber numberWithInt:10]];

just after this command i set up a break point and look at the scoreLog
but there nothing inside it?

any ideas?

robbieduncan · May 17, 2012

No where are you actually creating an NSMutableArray instance and assigning it to the property. All you have declared is a variable to store the instance and that it's a property with synthesized accessors. This does not magically create an array instance assigned to that property.

blue-lion · May 17, 2012

viewing arrays

sorry , I'm still a relative newbie

whats the difference between creating an instance, and declaring a variable to store an instance?

robbieduncan · May 17, 2012

blue-lion said:
sorry , I'm still a relative newbie

whats the difference between creating an instance, and declaring a variable to store an instance?

If you don't know that the best thing to do is stop writing code and go and read up on the very basics of programming. Essentially what is the difference between having a space to park a car and actually having a car?

ArtOfWarfare · May 17, 2012

blue-lion said:
whats the difference between creating an instance, and declaring a variable to store an instance?

Declaring a variable:

Code:

NSMutableArray *scoreLog;

Creating an instance (and calling init on it since those tend to go together...)

Code:

[[NSMutableArray alloc] init];

Doing both in one line:

Code:

NSMutableArray *scoreLog = [[NSMutableArray alloc] init];

Methods that create an instance are class methods that return an id or pointer to the instance that was created.

Class methods are the ones prefixed with a + (rather than a - ) in their declaration.

blue-lion · May 17, 2012

brilliant

thanks.

blue-lion · May 17, 2012

problems viewing contents of array

sorry, one further thought...

i assume i don't have to alloc-init on instance variables?, only arbitrary variables not part of any class?

robbieduncan · May 17, 2012

No object will exist unless you alloc/init it somewhere

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iOS problems viewing contents of array

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