Xcode Objective C while loop cannot access global variables - objective-c

Question

I'm very new to Xcode and Objective C. So most probably this is going to be an easy question (:
I'm trying to create an app that would do something if Caps Lock key is pressed.
And I need to see if Caps lock is pressed even if app is not in focus.
I've managed to check Caps Lock state even if my app is not in focus.
But I have an issue with getting out from while loop.
I cannot understand why my app cannot see what is happening to Caps lock key once it gets inside while loop.
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
_spam1 = NO;
[NSEvent addGlobalMonitorForEventsMatchingMask:NSFlagsChangedMask handler:^(NSEvent* event){
[NSThread sleepForTimeInterval:1];
if(event.keyCode == 0x39){ //CAPS LOCK key was pressed
if([event modifierFlags] & NSAlphaShiftKeyMask){
_spam1 = YES;
NSLog(#"caps lock is on");
} else {
_spam1 = NO;
NSLog(#"caps lock is off”);
}
//if I comment this part
//I can see if caps lock is on or off just fine
while(_spam1){
NSLog(#"Spam %#" , event);
NSLog(#"Spam %lu" , [event modifierFlags] & NSAlphaShiftKeyMask);
[NSThread sleepForTimeInterval:1];
if([event modifierFlags] & NSAlphaShiftKeyMask){
//_spam1 = YES;
} else {
_spam1 = NO;
NSLog(#“stop while loop”);
break;
}
}
}
}];
}

Answer 1

Work with framework, not agains:
Create a new subclass of NSView and override one of following methods. Set the new subclassed view in Interface builder. ( read more in Event handling guide )
So your code should look like this:
//multiKey handling
unichar SPACE_CHARACTER = 0x0020;
- (BOOL)performKeyEquivalent:(NSEvent *)theEvent
{
id responder = [[self window] firstResponder];
if (responder != self)
{
return [super performKeyEquivalent:theEvent];
}
NSUInteger numberOfPressedCharacters = [[theEvent charactersIgnoringModifiers] length];
NSEventType eventType = [theEvent type];
if (eventType == NSKeyDown && numberOfPressedCharacters == 1)
{
unichar key = [[theEvent charactersIgnoringModifiers] characterAtIndex:0];
if (key == SPACE_CHARACTER)
{
[self spaceBarPressed];
return YES;
}
}
return NO;
}
or
//single key handling (no modifiers like shift, ctrl...)
- (void)keyDown:(NSEvent *)theEvent
{
// code belongs here
}

Answer 2

Maybe I'm missing something, but why do you have the while loop at all, as your code comment says it works without it?
In outline what is happening is as follows:
Your call to addGlobalMonitorForEventsMatchingMask requests the system to call the block you pass every time an event occurs (that matches). This is done asynchronously, and for this to happen you must be going around your event loop.
The standard application model is event driven, the system sets up the main event loop and calls your code to handle the various events - including any required calls to your event monitoring block. After your code handles the event it returns, the event loop goes around and obtains the next event, calls your code to handle it, etc., etc.
When your block is called it is passed a reference to the event it needs to process. In a single call that event will not be changed asynchronously by the system - the system obtains the event as part of the event loop processing and calls your block, until that call returns the event loop cannot continue.
So after all that preamble what happens with your while loop is the call to sleepForTimeInterval causes your application to pause within the call to the block - the block does not return and so its caller, the event loop, does not continue either. On waking up your loop continues to process exactly the same event it was passed when called, your block then continues around its loop getting nowhere...
HTH