Start an action after timer - ios

Question

In my iOS app I've to do an action after a delay. I will explain it better: my app can recognize some audio frequency:
18100 Hz
18200 Hz
18300 Hz
18500 Hz
To do that I've modified the pitch detector. I want to start a timer when the device doesn't recognize one of the frequency that I've setter up in my app.
I made so:
- (void)frequencyChangedWithValue:(float)newFrequency {
frequencyRecived = newFrequency;
watermarkReceived = YES;
if (frequencyRecived > 18000) {
if (frequencyRecived >= 18000 && frequencyRecived <= 18110 && !water1) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"1"];
water2 = water3 = water4 = NO;
water1 = YES;
}
if (frequencyRecived >= 18115 && frequencyRecived <= 18250 && !water2) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"2"];
water1 = water3 = water4 = NO;
water2 = YES;
}
if (frequencyRecived >= 18255 && frequencyRecived <= 18440 && !water3) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"3"];
water1 = water2 = water4 = NO;
water3 = YES;
}
if (frequencyRecived >= 18450 && !water4) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"4"];
water1 = water2 = water3 = NO;
water4 = YES;
}
} else {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"Nessuna postazione"];
water1 = water2 = water3 = water4 = NO;
}
}
In the else section I've to start a timer that it count for 10 seconds, after this time I've to write a label. I tried to use the following solution:
[self performSelector:<#(SEL)#> withObject:<#(id)#> afterDelay:<#(NSTimeInterval)#> inModes:<#(NSArray *)#>]
, but it never call the selector method because every time the app execute the code in else it restart the timer.
Can you suggest me a solution to solve this issue?
Thanks
UPDATE
I follow the answer, but it doesn't work. I post here the code updated:
#interface ViewController () {
BOOL watermarkReceived;
float frequencyRecived;
CABasicAnimation *theAnimation;
BOOL water1, water2, water3, water4;
}
#property(nonatomic,strong)NSTimer *timer;
#end
- (void)frequencyChangedWithValue:(float)newFrequency {
frequencyRecived = newFrequency;
watermarkReceived = YES;
if (frequencyRecived > 18000) {
[self.timer invalidate];
self.timer = nil;
if (frequencyRecived >= 18000 && frequencyRecived <= 18110 && !water1) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"1"];
water2 = water3 = water4 = NO;
water1 = YES;
}
if (frequencyRecived >= 18115 && frequencyRecived <= 18250 && !water2) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"2"];
water1 = water3 = water4 = NO;
water2 = YES;
}
if (frequencyRecived >= 18255 && frequencyRecived <= 18440 && !water3) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"3"];
water1 = water2 = water4 = NO;
water3 = YES;
}
if (frequencyRecived >= 18450 && !water4) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"4"];
water1 = water2 = water3 = NO;
water4 = YES;
}
} else {
self.timer = [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:#selector(noPosition) userInfo:nil repeats:NO];
// [self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"Nessuna postazione"];
water1 = water2 = water3 = water4 = NO;
}
}
- (void)noPosition {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"Nessuna postazione"];
}
PS: I understood the other problems you told me and I will solve in the future, for now I need to fix the timer issue. :)

Answer 1

Use an NSTimer. In the else branch, check if the timer already exists and, if not, create and schedule it. In the main branch of the if, invalidate and destroy the timer.
Also, your if statement has a number of holes and is overly complex. You have already checked that the frequency is > 18000 so you don't need to check it again. You are also using if, else if to simplify because each is a distinct range, and if one range is detected then none of the other ranges can be. In this way you can just check that the upper range bound is not exceeded in the inner if.
Also, setting the text in the background looks wrong. UI updates need to be made from the main thread
Something like:
- (void)frequencyChangedWithValue:(float)newFrequency {
frequencyRecived = newFrequency;
watermarkReceived = YES;
if (frequencyRecived > 18000) {
[self.timer invalidate];
self.timer = nil;
if (frequencyRecived <= 18110) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"1"];
water2 = water3 = water4 = NO;
water1 = YES;
}
else if (frequencyRecived <= 18250) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"2"];
water1 = water3 = water4 = NO;
water2 = YES;
}
else if (frequencyRecived <= 18440) {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"3"];
water1 = water2 = water4 = NO;
water3 = YES;
}
else {
[self performSelectorInBackground:#selector(setTextInLabel:) withObject:#"4"];
water1 = water2 = water3 = NO;
water4 = YES;
}
} else {
if (self.timer == nil) {
self.timer = [NSTimer scheduledTimerWithTimeInterval:... target:self selector:... userInfo:nil repeats:NO];
}
water1 = water2 = water3 = water4 = NO;
}
}