initialize instance variables on Objective-C

Question

I'm developing an iPhone 3.1.3 application and I have the following header file:

#import <UIKit/UIKit.h>

@interface VoiceTest01ViewController : UIViewController {
    IBOutlet UITextView *volumeTextView;
    BOOL isListening;
    NSTimer *soundTimer;
}

@property (nonatomic, retain) IBOutlet UITextView *volumeTextView;
@property (nonatomic, retain) NSTimer *soundTimer;

- (IBAction)btnStartClicked:(id)sender;

@end

And .m file is:

#import "VoiceTest01ViewController.h"

@implementation VoiceTest01ViewController

@synthesize volumeTextView;
@synthesize soundTimer;

...

How can I set isListening up to false at start?

DarkDust · Accepted Answer · 2011-03-02 14:19:37Z

6

All instance variables are set to 0/NULL/nil by default, which in the case of a BOOL means NO. So it already is NO (or false) by default.

If you need any other value then you need to override the designated initializer(s), most of the time init, and set the default value there.

answered Mar 2, 2011 at 14:19

DarkDust

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Comments

smorgan · Accepted Answer · 2011-03-02 14:31:04Z

3

Set the boolean value in your viewDidLoad

- (void)viewDidLoad {
  isListening = NO;
  //Something
}

edited Mar 2, 2011 at 14:31

smorgan

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answered Mar 2, 2011 at 14:17

ipraba

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2 Comments

James Bedford Over a year ago

Yea - @VansFannel, be sure to check out the UIViewController documentation for this as to why this is the case for this type of class. :)

GaryO Over a year ago

This is so lame -- not your answer, @iPrabu, which is correct, but the fact that the objective-c language doesn't let you specify initializers for instance variables. The fact that you have to do it in some OS- and app-specific way is just sad (or override the designated initializer as @DarkDust says, but that's even more of a pain just to add what should be a simple = 1).

xlarsx · Accepted Answer · 2011-03-02 14:23:06Z

2

The default value for a BOOL field is False, but it's a good place set it in the "viewDidLoad" just as @BuildSucceeded sugest

Greetings

answered Mar 2, 2011 at 14:23

xlarsx

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Comments

William Hu · Accepted Answer · 2015-11-22 10:59:17Z

1) init is a good place, like below, but if you are using story board this init method won't be called.

- (id) init {
    self = [super init];
    if (self) {
        isListening = NO;
    }
    return self;
}

2) initWithCoder is a good place for your code if you are using storyboard of course your sdk is 3.0, i believe it has not storyboard at that time, but just in case anyone need it:

- (id) initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        isListening = NO;
    }
    return self;
}

3) If your viewcontroller will be init from nib file:

- (id) initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
         isListening = NO;
    }
}

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