iOS can we reuse a NSTimer - ios

Question

I want to use an NSTimer (or if you have a better suggestion) to play a sound when the device is unplugged, or unknown. However if the user plugs the device back in, the sound should immediately stop.
Here's my code but it doesn't seem to behave as I am describing it,
- (void)currentBatteryState
{
UIDevice *device = [UIDevice currentDevice];
switch(device.batteryState) {
case UIDeviceBatteryStateUnknown:
currentBatteryStatusLabel.text = #"Unknown";
if ([batteryControlTimer isValid]) {
[batteryControlTimer invalidate];
batteryControlTimer = [NSTimer scheduledTimerWithTimeInterval:2.5 target:self selector:#selector(playSound) userInfo:nil repeats:YES];
} else {
batteryControlTimer = [NSTimer scheduledTimerWithTimeInterval:2.5 target:self selector:#selector(playSound) userInfo:nil repeats:YES];
}
break;
case UIDeviceBatteryStateUnplugged:
currentBatteryStatusLabel.text = #"Unplugged";
if ([batteryControlTimer isValid]) {
[batteryControlTimer invalidate];
batteryControlTimer = [NSTimer scheduledTimerWithTimeInterval:2.5 target:self selector:#selector(playSound) userInfo:nil repeats:YES];
} else {
batteryControlTimer = [NSTimer scheduledTimerWithTimeInterval:2.5 target:self selector:#selector(playSound) userInfo:nil repeats:YES];
}
break;
case UIDeviceBatteryStateCharging:
currentBatteryStatusLabel.text = #"Charging";
[batteryControlTimer invalidate];
break;
case UIDeviceBatteryStateFull:
currentBatteryStatusLabel.text = #"Full";
[batteryControlTimer invalidate];
break;
}
}
- (void) playSound
{
CFBundleRef mainBundle = CFBundleGetMainBundle();
CFURLRef soundFileURLRef;
soundFileURLRef = CFBundleCopyResourceURL(mainBundle, (CFStringRef) #"siren_1", CFSTR ("mp3"), NULL);
UInt32 soundID;
AudioServicesCreateSystemSoundID(soundFileURLRef, &soundID);
AudioServicesPlaySystemSound(soundID);
}
Thank you

Answer 1

If the condition isn't met, don't play any sound, but don't invalidate the timer. That way it will keep firing at the interval even if the condition isn't met once.
So:
- (void)playSound {
if(conditionIsMet) {
//code to play your sound
}
}
Edit:
If you want to make the interval at which the sound can stop because the condition isn't met, then you just need to make the timer's time interval and the duration of the sound smaller.