Constructors, Static Methods and Class variables in Objective C

Question

Just trying to convert some Java code into Objective-C.

Here is a snippet of the code for the constructor of a class called 'bone' written in Java.

public class Bone {

public static double            RADS_TO_DEGS =
                                Quaternion.RADS_TO_DEGS;
public static double            DEGS_TO_RADS =
                                Quaternion.DEGS_TO_RADS;

public static int               LUPA_4CC =
                                FourCCUtil.fourCCInt("LUPA");
public static int               RUPA_4CC =
                                FourCCUtil.fourCCInt("RUPA");
public static int               LLRA_4CC =
                                FourCCUtil.fourCCInt("LLRA");
public static int               RLRA_4CC =
                                FourCCUtil.fourCCInt("RLRA");

protected float                 length;
protected Bone                  parent;
protected Bone[]                childBones;
protected int                   fourCCName;
protected int                   parentFourCCName;
protected float[]               translation;

Here is my attempt at rewriting this code in objective-c:

bone.h

@interface Bone : NSObject{

@property static double         RADS_TO_DEGS;
@property static double         DEGS_TO_RADS;

@property static int                LUPA_4CC;
@property static int                RUPA_4CC;
@property static int                LLRA_4CC;
@property static int                RLRA_4CC;


@protected {
    @property float length;
    @property Bone parent;
    @property Bone[] childBones ;
    @property int fourCCName;
    @property int parentFourCCName;
    @property float[] translation;

bone.m

@implementation VA_Bone

-(id)init{

    self=[super init];
    if(self){

        VA_4ccUtil       *FCC       = [[VA_4ccUtil alloc] init];
        VA_Bone          *Bone      = [[VA_Bone alloc] init];
        VA_TRTransform   *TRTform   = [[VA_TRTransform alloc] init];
        VA_TRUtil        *TRUtil    = [[VA_TRUtil alloc] init];
        VA_Quaternion    *Quat      = [[VA_Quaternion alloc] init]];           

       [Bone setDEGS_TO_RADS: [Quat DEGS_TO_RADS]];
       [Bone setRADS_TO_DEGS: [Quat RADS_TO_DEGS]];

       [Bone setLUPA_4CC: [TRUtil fourCCInt:"LUPA"]];
       [Bone setRUPA_4CC: [TRUtil fourCCInt:"RUPA"]];
       [Bone setLLRA_4CC: [TRUtil fourCCInt:"LLRA"]];
       [Bone setRLRA_4CC: [TRUtil fourCCInt:"RLRA"]];

        [self setParent:NULL];
        [self setFourCCName:0];
        [self setParentFourCCName:0];
        [self setTranslation:NULL];
        [self setLength:0];

    }
    return self;
}

My questions are:

1) Have I declared the static methods correctly?

2) Is it possible to assign class types or is it better to use an array such as NSMutableArray instead of Bone[]?

I am still trying to get my head around how to construct a class in objective-c since I am currently converting some Java code into objective c.

Kind Regards, Sam

I suggest you to read an Objective-C introduction before attempting to write any code. Clearly you miss the basics. — Gabriele Petronella
– Gabriele Petronella, Commented Jan 27, 2013 at 21:42

Sergey Kalinichenko · Accepted Answer · 2013-01-27 21:49:05Z

4

Have I declared the static methods correctly?

No. There is no such thing as @property static in Objective C. You need to declare them as class methods:

+(double)RADS_TO_DEGS; // This is a getter

If you need a setter, write one more method:

+(void)setRADS_TO_DEGS:(double)val; // This is a setter

Is it possible to assign class types or is it better to use an array such as NSMutableArray instead of Bone[]?

Plain C arrays are problematic because of the ownership problem. You will be better served with a NSArray property: it would give you the same flexibility, provide your clients with fast enumeration, and deal with resource cleanup in ways idiomatic to Objective C.

answered Jan 27, 2013 at 21:49

Sergey Kalinichenko

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4 Comments

samb90 Over a year ago

Ok thank you very much for your help, I will have another look at my code and make the changes

samb90 Over a year ago

Am I able to use this property "@property Bone[] childBones;" or do i need to make "Bone[]" type "NSArray"?

Sergey Kalinichenko Over a year ago

@samb90 No, you need to use @property (readonly) Bone *childBones;, and publish the length of childBones array separately, for example @property (readonly) int childBoneCount;

Jonathan Grynspan Over a year ago

That won't work. Bone * is already a pointer to a Bone object, but objects are dynamically allocated one-by-one, so it will never be an array of Bone objects. You can either have a C array of Bone * (Bone **) or an NSArray. Cocoa style generally strongly prefers the latter.

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