Slow down NSTimer with a for loop in Objective-C - ios

Question

I have a button that when pressed generates random numbers triggered by NSTimer at a certain frequency, and when released I would like it to keep generating them, just more slower and slower until it stops.
- (void)buttonPressed {
_timer = [NSTimer scheduledTimerWithTimeInterval:0.2 target:self selector:#selector(generateNumber) userInfo:nil repeats:YES];
}
- (void)buttonReleased {
if ([_timer isValid]) {
[_timer invalidate];
}
_timer = nil;
for (float i=0.20; i<1; i += 0.1) {
_timer = [NSTimer scheduledTimerWithTimeInterval:i target:self selector:#selector(generateNumber) userInfo:nil repeats:NO];
}
}
It works fine while the button is pressed, but once I release it actually accelerate and then stops all in a sudden. Any idea why it wouldn't be working or any alternative way I can reach the wanted result?

Answer 1

Once your button is released, generation accelerates because at that moment you schedule 8 timers with intervals 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 starting at the time of button release, which means each will execute 0.1s after the other, which is a smaller interval than your original timer (0.2s).
This is an alternative
#interface ViewController ()
#property (nonatomic, retain) NSTimer *timer;
#property (nonatomic) float curInterval;
#end
#implementation ViewController
- (IBAction)buttonDown {
self.curInterval = 0.1;
[self updatePressed];
}
- (void)updatePressed {
[self generateNumber];
self.timer = [NSTimer scheduledTimerWithTimeInterval:self.curInterval target:self selector:#selector(updatePressed) userInfo:nil repeats:NO];
}
- (IBAction)buttonUp {
[self.timer invalidate];
[self updateUp];
}
- (void)updateUp {
[self generateNumber];
self.curInterval += 0.1;
if (self.curInterval < 1.0f) {
self.timer = [NSTimer scheduledTimerWithTimeInterval:self.curInterval target:self selector:#selector(updateUp) userInfo:nil repeats:NO];
}
}
#end

Answer 2

In Button release method you are using for loop which keeps on executing untill it reaches interval of 1. What you need to do is take a global float value and initialize it to 0.20 at start. On button pressed pass that value. On button release increment the global variable and pass that value to NSTimer instead of for loop
float numTimer = 0.20f;
- (void)buttonPressed {
_timer = [NSTimer scheduledTimerWithTimeInterval:numTimer target:self selector:#selector(generateNumber) userInfo:nil repeats:YES];
}
- (void)buttonReleased {
if ([_timer isValid]) {
[_timer invalidate];
}
_timer = nil;
numTimer = numTimer + 0.1f;
_timer = [NSTimer scheduledTimerWithTimeInterval:numTimer target:self selector:#selector(reGenerateNumber) userInfo:nil repeats:NO]; }
}
-(void) reGenerateNumber {
[self generateNumber];
if ([_timer isValid]) {
[_timer invalidate];
}
_timer = nil;
numTimer = numTimer + 0.1f;
_timer = [NSTimer scheduledTimerWithTimeInterval:numTimer target:self selector:#selector(reGenerateNumber) userInfo:nil repeats:NO];
}