Question

I’m new to iOS Dev, I’m following the Stanford CS193P classes for Fall 2010. I’m on assignment 3 and I’m setting my delegate to my view and by using the debugger I’m noticing the call to my delegate method won’t happen, I don’t understand what could be happening. My code is as follows:

GraphViewController.h:

@interface GraphViewController : UIViewController <GraphViewDelegate> {
    GraphView *graphView;
    float scale;
}

@property (retain) IBOutlet GraphView *graphView;
@property float scale;

- (IBAction)zoomIn;
- (IBAction)zoomOut;

@end

GraphViewController.m:

@implementation GraphViewController

@synthesize graphView, scale;

- (NSString *)functionForGraph:(GraphView *)requestor {
    NSLog(@"%@", @"culo peluo");
    return @"lol";
}

- (float)scaleForGraph:(GraphView *)requestor {
    return self.scale;
}

- (IBAction)zoomIn {

}

- (IBAction)zoomOut {

}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

    }
    return self;
}

- (void)dealloc
{
    [super dealloc];
}

- (void)didReceiveMemoryWarning
{
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.graphView.delegate = self;
    self.scale = 20;
    [self.graphView setNeedsDisplay];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

@end

GraphView.h:

@class GraphView;

@protocol GraphViewDelegate 
- (NSString *)functionForGraph:(GraphView *)requestor;
- (float)scaleForGraph:(GraphView *)requestor;
@end

@interface GraphView : UIView {
    id <GraphViewDelegate> delegate;
}

@property (assign) id <GraphViewDelegate> delegate;

@end

GraphView.m:

@implementation GraphView

@synthesize delegate;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
    }
    return self;
}

- (void)drawRect:(CGRect)rect
{
    CGFloat cgScale = [self.delegate scaleForGraph:self];
    [AxesDrawer drawAxesInRect:self.bounds originAtPoint:self.center scale:cgScale]; 
}


- (void)dealloc
{
    [super dealloc];
}

@end

Answer 1

1. Put a break point on the line where you set the graph view’s delegate.
2. Inspect the graphView variable. Is it nil?

This happens to me all the time and it’s always (well nearly always) because I have failed to connect the outlet to the view in interface builder.