Objective-C dot syntax or property value?

Question

I keep reading that dot syntax is possible but I keep getting errors that the struct does not contain members I am referencing. Perhaps its not the dot syntax so I have included details of what I am doing in hopes of a solution:

//  MobRec.h - used as the objects in the MobInfo array
#import <Foundation/Foundation.h>

@interface MobRec : NSObject {
@public NSString *mName;        
     @public int mSpeed;
}

@property (nonatomic, retain) NSString *mName; 
@property (nonatomic) int mSpeed;

// MobDefs.h - array of MobRecords
@interface Mobdefs : NSObject {
@public NSMutableArray *mobInfo;
}

@property(assign) NSMutableArray *mobInfo;  // is this the right property?

-(void) initMobTable;

@end

// MobDefs.m
#import "Mobdefs.h"
#import "Mobrec.h"
@implementation Mobdefs
@synthesize mobInfo;

-(void) initMobTable 
{
    // if I use traditional method I get may not respond 
    [mobInfo objectAtIndex:0 setmName: @"doug"];

    // if I use dot syntax I get struct has no member named mName 
    mobInfo[1].MName = @"eric";
}

// main.h
MobDefs *mobdef;

// main.m 
mobdef = [[Mobdefs alloc] init];
[mobdef initMobTable];

although both methods should work I get erros on both. What am I doing wrong? My best thoughts have been that I am using the wrong @property but I think I have tried all. I am performing alloc in main. Ideally I would like to for this use dot syntax and cant see why its not allowing it.

Answer 1

[mobInfo objectAtIndex:0 setmName: @"doug"];

There is no objectAtIndex:setmName method, so you're going to have to explain what you think this is even supposed to do.

mobInfo[1].MName = @"eric";

Use objectAtIndex to look something up in an NSArray object.

Answer 2

A couple of things: (edit: original point #1 removed due to error)

1. Although the dot syntax is supported, the array index syntax for NSArray is not. Thus, your call to mobInfo[1] will not be the same as [mobInfo objectAtIndex:1]; Instead, mobInfo will be treated as a simple C-style array, and that call would be almost guaranteed to result in a crash.

2. You should not define variables in your header file as you do in main.h. The line MobDefs *mobdef; belongs somewhere in main.m.

edit: Here is how it should look:

MobRec.h

@interface MobRec : NSObject {
    NSString *mName;        
    int mSpeed;
}

@property (nonatomic, retain) NSString *mName; 
@property (nonatomic) int mSpeed;

MobRec.m

@implementation MobRec
@synthesize mName;
@synthesize mSpeed;
@end

MobDefs.h

@interface MobDefs : NSObject {
    NSMutableArray *mobInfo;
}
@property(assign) NSMutableArray *mobInfo;
-(void) initMobTable;
@end

MobDefs.m

#import "MobDefs.h"
#import "MobRec.h"

@implementation MobDefs
@synthesize mobInfo;

-(void) initMobTable 
{
    // option 1:
    [(MobRec*)[mobInfo objectAtIndex:0] setMName:@"doug"];

    // option 2:
    (MobRec*)[mobInfo objectAtIndex:0].mName = @"eric";

    // option 3:
    MobRec *mobRec = [mobInfo objectAtIndex:0];
    mobRec.mName = @"eric";
}

main.m

MobDef *mobdef = [[MobDefs alloc] init];
[mobdef initMobTable];
...
[mobdef release]; // don't forget!

Answer 3

You need to either cast the object returned by -objectAtIndex:, or use a method call on it:

[[mobInfo objectAtIndex: 0] setMName: @"doug"];

or

((Mobrec *) [mobInfo objectAtIndex: 0]).MName = @"doug";