Xcode os x : Why drawRect could not access instance data - objective-c

Question

I am trying to draw something in my custom view, but not sure why drawRect could not access its instance data. Here is the steps I tried.
Create a Mac OS X app, with using storyboard checked.
In the storyboard, delete the view, then add a new custom view under the view at the same place. (I tried if the view is not deleted, same).
Assign EEGView class to the newly added custom view.
then run. From the log information, you will notice that the drawRect could not access the instance data although the instance variables get initialized and updated.
In viewCtroller.m
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
myView = [[EEGView alloc] init];
//[self.view addSubview:myView];
//Start Timer in 3 seconds to show the result.
NSTimer* _timerAppStart = [NSTimer scheduledTimerWithTimeInterval:2
target:self
selector:#selector(UpdateEEGData)
userInfo:nil
repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:_timerAppStart forMode:NSDefaultRunLoopMode];
}
- (void)UpdateEEGData
{
// NSLog(#"UpdateEEGData.....1");
// myView.aaa = 200;
// myView.nnn = [NSNumber numberWithInteger:myView.aaa];
// make sure this runs on the main thread
if (![NSThread isMainThread]) {
// NSLog(#"NOT in Main thread!");
[self performSelectorOnMainThread:#selector(updateDisplay) withObject:nil waitUntilDone:TRUE];
}else
{
[self.view setNeedsDisplay:YES];
}
NSLog(#"UpdateEEGData.....2");
[myView setAaa:400];
myView.nnn = [NSNumber numberWithInteger:myView.aaa];
// make sure this runs on the main thread
if (![NSThread isMainThread]) {
// NSLog(#"NOT in Main thread!");
[self performSelectorOnMainThread:#selector(updateDisplay) withObject:nil waitUntilDone:TRUE];
}else
{
[self.view setNeedsDisplay:YES];
}
}
-(void)updateDisplay
{
[self.view setNeedsDisplay:YES];
}
In my custom view class EEGView.m
#implementation EEGView
#synthesize aaa;
#synthesize nnn;
-(id)init{
self = [super init];
if (self) {
aaa = 10;
nnn = [NSNumber numberWithInteger:aaa];
NSLog(#"init aaa: %i", aaa);
NSLog(#"init nnn: %i", [nnn intValue]);
}
return self;
}
- (void)drawRect:(NSRect)dirtyRect {
[super drawRect:dirtyRect];
// Drawing code here.
NSLog(#"drawRect is here");
NSLog(#"drawRect aaa: %i", aaa);
NSLog(#"drawRect nnn: %i", [nnn intValue]);
}
#end
Did I miss anything? Tested in Xcode 7.2 & 7.2. But if I leave the 'using storyboard' unchecked, it works.
Or is it a Xcode bug?
Any advice appreciated.
Thanks in advance.

Answer 1

If you've added EEGView view on storyboard, you shouldn't be also instantiating one in viewDidLoad. You've alloc/init'ed a new one, but it bears no relationship to the one that the storyboard created for you. So, the one created by the storyboard has drawRect called, but you're setting the properties in the separate instance that you created in viewDidLoad which was never added to the view hierarchy (and thus never will have its drawRect called).
When the storyboard instantiates the view controller's view, it will instantiate your EEGView for you. All you need to do is to hook up an IBOutlet for this view in order to get a reference to it from your view controller. (For example, you can control drag from the EEGView in the storyboard scene to the #interface for the view controller that you've pulled up in the assistant editor.)