XCode View Controller Not Updating in Do Loop - xcode

Question

I have a do loop that I want to execute a command every 1 second while a SWITCH is on.
The Code works fine ONCE, when I don't have the DO LOOP.
However, as soon as I add the LOOP, none of the labels in the view controller are updated, the back button for the storyboard doesn't work, and the SWITCH will not toggle off. Essentially, the DO LOOP keeps looping, but nothing on the screen will work, nor can I back out.
I know I'm doing it wrong. But, I don't now what. Any thoughts would be appreciated.
I attached the code that gets me in trouble.
Thanks,
- (IBAction)roaming:(id)sender {
UISwitch *roamingswitch = (UISwitch *)sender;
BOOL isOn = roamingswitch.isOn;
if (isOn) {
last=[NSDate date];
while (isOn)
{
current = [NSDate date];
interval = [current timeIntervalSinceDate:last];
if (interval>10) {
TheCommand.text=#"ON";
[self Combo:sendcommand];
last=current;
}
}
}
else
{
TheCommand.text=#"OFF";
}
}

Answer 1

iOS and OSX are event based systems and you cannot use loops like this in the main (UI) thread to do what you want to do, otherwise you don't allow the run loop to run and events stop being processed.
See: Mac App Programming Guide section "The App’s Main Event Loop Drives Interactions".
What you need to do is set-up a timer (NSTimer) which will fire every second:
.h file:
#interface MyClass : NSView // Or whatever the base class is
{
NSTimer *_timer;
}
#end
.m file:
#implementation MyClass
- (id)initWithFrame:(NSRect)frame // Or whatever the designated initializier is for your class
{
self = [super initInitWithFrame:frame];
if (self != nil)
{
_timer = [NSTimer timerWithTimeInterval:1.0
target:self
selector:#selector(timerFired:)
userInfo:nil
repeats:YES];
}
return self;
}
- (void)dealloc
{
[_timer invalidate];
// If using MRR ONLY!
[super dealloc];
}
- (void)timerFired:(NSTimer*)timer
{
if (roamingswitch.isOn)
{
TheCommand.text=#"ON";
[self Combo:sendcommand];
}
}
#end

Answer 2

Give your processor enough time to update your view controller and not be interrupted by other processes. I give it 0.5 second before and after the view controller update signal.
[[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.5]];
self.CrashingTime.text = [NSString stringWithFormat: #"Crash Time = %f ms", outputOfCrashTime];
[[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.5]];