Obj-C: Delegate method not getting called - objective-c

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

Put a break point on the line where you set the graph view's delegate.
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.

Answer 2

Let's say class YourClass is a delegate for some other class. And delegate methods are not called, despite that delegate property is set up.
Most probably the problem is that your class instance, that is a delegate for your other class is released before the delegate method is called on it. Make it more persistent by making this class a property or instance variable of other class or by using dispatch_once. For example,
Change
YourClass *instance = [[YourClass alloc] init];
by
#property(nonatomic, strong) YourClass *instance;
self.instance = [[YourClass alloc] init];
This problem occurs because in ARC everything that is created inside a method (and is not an instance variable) is released, when method finishes. And delegate methods cannot be called, that are invoked by some background process.
I've written a big blog post on this problem. This is pretty common situation.
http://alwawee.com/wordpress/2013/07/31/on-xmppframework-delegate-method-not-being-called/

Answer 3

Ive got a few pointers for ya on this one:
You don't need an iVar (internal Variable) if you have the variable as a property, it will still work, I've never know it not to.
GraphView
#interface GraphView : UIView {
}
#property (assign) id <GraphViewDelegate> delegate;
#end
GraphViewController
#interface GraphViewController : UIViewController <GraphViewDelegate> {
}
#property (retain) IBOutlet GraphView *graphView;
#property float scale;
- (IBAction)zoomIn;
- (IBAction)zoomOut;
#end
You need to set your delegate in your view to be able to use it.
GraphViewController
#implementation GraphViewController
( ... )
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
self.delegate = self;
}
return self;
}
( ... )
#end

Answer 4

You are not calling the delegate functions anywhere in your GraphView.m. Try testing it out by placing this piece of code in your - (id)initWithFrame:(CGRect)frame method, right before you return.
[self.delegate functionForGraph:nil];
and see if it logs any message to the console.
Of course this is just to test the delegate implementation, you should actually be using this delegate call in some other method in your GraphView.m which is able to process your requestor