Question

I did the “Build and analyze” in xCode and get “Dereference of null pointer” . I noted in my code below for which row I get the message. I’m developing for iPhone.

“PDFScrollView.h”

 #import "ENsightAppDelegate.h"
@interface PDFScrollView : UIScrollView <UIScrollViewDelegate> {

ENsightAppDelegate *appDelegate;
}

 @end

“PDFScrollView.m”

 - (id)initWithFrame:(CGRect)frame
{
if ((self = [super initWithFrame:frame])) {

    // Set up the UIScrollView
    self.showsVerticalScrollIndicator = NO;
    self.showsHorizontalScrollIndicator = NO;
    self.bouncesZoom = YES;
    //self.decelerationRate = UIScrollViewDecelerationRateFast;
    self.delegate = self;
    [self setBackgroundColor:[UIColor grayColor]];
    self.maximumZoomScale = 5;//200
    self.minimumZoomScale = 0.5;//.85
    self.userInteractionEnabled = YES;
    self.delaysContentTouches = YES;
    self.canCancelContentTouches = NO;

}
appDelegate =(ENsightAppDelegate *) [[UIApplication sharedApplication] delegate];
pdfView=[appDelegate GetLeaveView];
[self addSubview:pdfView];
return self;

}

It’s not the complete code, pasted what I think is useful.

I find this quite strange. How come I get this message?

Answer 1

If self is nil, then you can’t access instance variables of ‘self’. So you should reference those variables only inside of the if statement. In other words, only if self is not nil.

- (id)initWithFrame:(CGRect)frame {

   if ((self = [super initWithFrame:frame])) {

      // Set up the UIScrollView
      self.showsVerticalScrollIndicator = NO;
      // ... bunch of other properties set...
      // ... btw, better style here would be to set the ivars directly (in an initializer)

      appDelegate =(ENsightAppDelegate *) [[UIApplication sharedApplication] delegate];
      pdfView=[appDelegate GetLeaveView];
      [self addSubview:pdfView];
    }

    return self;
}