Passing over Object between Classes not working - objective-c

Question

hey guys,
i'm new to objective-c and i'm having trouble with the memory management. i declared 3 classes, Table, Dataset and my Main class. In my mainclass, i created an Dataset Object and now im trying to pass this Object over to a Tableobject, where i want to store it permanently. but it seems to me that the garbage collector kills the reference before i can use it.
heres some code:
Dataset:
//Dataset.h
#interface Dataset : NSObject {
NSMutableArray* daten;
}
#end
//Dataset.m
#import "Dataset.h"
#import "Datensatz.h"
#implementation Dataset
- (id) init
{
self=[super init];
daten=[[NSMutableArray alloc] init];
return self;
}
Table:
//Table.h
#class Dataset;
#interface Table : NSObject {
Dataset* daten;
}
-(id)init:(NSTableView *)aTableView;
-(id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex;
- (NSInteger)numberOfRowsInTableView:(NSTableView *)aTableView;
#property (retain) Dataset* daten;
#end
//Table.m
#import "Table.h"
#import "Dataset.h"
#impl
ementation Table
#synthesize daten;
-(id)init:(NSTableView*)aTableView
{
self=[super init];
[self setDaten:[Datenmenge alloc]];
return self;
}
- (NSInteger)numberOfRowsInTableView:(NSTableView *)aTableView
{
NSLog(#"anzahl: %d %#",[self.daten anzahl], self.daten);//This is always 0 null
return [daten anzahl];
}
-(void)setDaten:(Dataset *)a
{
NSLog(#"setter: anzahl: %d %#",[a anzahl], a);
[daten release];
daten=[a retain];
NSLog(#"setter: anzahl: %d %#",[daten anzahl], daten);
}
#end
In my mainclass i do the following:
//init method
[self setDaten:[[[Dataset alloc]init]autorelease]];
tabelle=[[Table alloc] init:tableview];
[tabelle setDaten:[self daten]];
Mainclass:
//code.h
//
// MalWiederWasNeuesAppDelegate.h
// MalWiederWasNeues
//
// Copyright 2011 __MyCompanyName__. All rights reserved.
//
#import <Cocoa/Cocoa.h>
#class Datenmenge,Graph,Tabelle;
#interface MalWiederWasNeuesAppDelegate : NSObject <NSApplicationDelegate> {
NSWindow *window;
NSToolbarItem *datenKnopf;
NSToolbarItem *speichernKnopf;
NSSlider *scaleSlider;
NSScroller *moveSlider;
NSTableView* tableview;
Graph* graph;
Tabelle* tabelle;
Datenmenge* daten;
}
-(void)tuWas;
- (IBAction)datenHinzufuegen:(id)sender;
- (IBAction)speichern:(id)sender;
#property (assign) IBOutlet NSWindow *window;
#property (assign) IBOutlet NSToolbarItem *datenKnopf;
#property (assign) IBOutlet NSToolbarItem *speichernKnopf;
#property (assign) IBOutlet NSSlider *scaleSlider;
#property (assign) IBOutlet NSScroller *moveSlider;
#property (assign) IBOutlet Graph *graph;
#property (assign) IBOutlet Tabelle *tabelle;
#property (assign) IBOutlet NSTableView* tableview;
#property (retain) Datenmenge* daten;
#end
//code.m
//
// MalWiederWasNeuesAppDelegate.m
// MalWiederWasNeues
//
// Copyright 2011 __MyCompanyName__. All rights reserved.
//
#import "MalWiederWasNeuesAppDelegate.h"
#import "Datenmenge.h"
#import "Graph.h"
#import "Tabelle.h"
#implementation MalWiederWasNeuesAppDelegate
#synthesize window;
#synthesize daten;
-(id) init
{
self.daten=[[Datenmenge alloc]init];
[self.daten datenHinzufuegen:nil];
tabelle=[[Tabelle alloc] init:tableview];
tabelle.daten=daten;
NSLog(#"konstruktor: %f %d",[daten maximum],[daten anzahl]);
//graph.daten=daten;
return self;
}
-(void)tuWas{
}
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Insert code here to initialize your application
}
- (IBAction)datenHinzufuegen:(id)sender
{
NSLog(#"%f %d",[daten maximum],[daten anzahl]);
NSLog(#"daten hinzufügen");
}
- (IBAction) speichern:(id)sender
{
NSLog(#"%# %#",daten,[tabelle daten]);
NSLog(#"speichern");
}
#end
I hope this wasnt too much code for you.
when i call a method of "tabelle", my Table object, "daten" does not refer to an Dataset Object. But the NSLogs in "setDaten" show me valid references.
so, what am i doing wrong?
have a good evening,
lukas

Answer 1

You define Daten as a retain type
#property (retain) Dataset* daten; and #synthesize daten;
theres no need to then implement the method
-(void)setDaten:(Dataset *)a thats what #synthesize daten; does
I think theres a lost in translation moment here so ill assume Table == Tabelle and Dataset == Datmenge and I dont see the implementation for your main class.
cast your eye over this too.
http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProperties.html

Answer 2

Maybe, the daten property of your main class is declared as assign? In that case daten is correct when you call setDaten:, but might have been already autoreleased when you try to access it afterwards.
Also,
-(void)setDaten:(Dataset *)a
{
NSLog(#"setter: anzahl: %d %#",[a anzahl], a);
[daten release];
daten=[a retain];
NSLog(#"setter: anzahl: %d %#",[daten anzahl], daten);
}
is not a good implementation of a setter. If a == daten, then this object will be released (and maybe dealloc'd). You need to check identity of objects when implementing your own setter.