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Now, if you manage to complete the challenge from the last lesson, then this should be the effect that
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you now have. When you press on one of these buttons,
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so the Soft button, the countdown timer should start from 300,
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Medium starts from 420, and Hard starts from 720.
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So now if I press on the Soft button, you'll see that I'm getting a countdown timer that fires every
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second
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counting down the amount of time that my egg still has to cook.
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Now, if you haven't got this effect or you don't know what I'm talking about, then you might have missed
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out on the last lesson which was a challenge
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lesson. So be sure to complete the challenge, so that we can actually move on. Now, if you have completed
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the challenge, then I want to go through the code that I've got and you can compare it to yours as well.
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So the first thing that we did was we converted our minutes to seconds because we're going to be counting
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down every second. And then we created a variable code secondsRemaining to keep track of how many
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seconds there are.
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And then when the user selected the hardness that they wanted, we assigned the value in our eggTimes
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dictionary, so be it 300, 420, or 720 to the variable secondsRemaining.
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So at this point, secondsRemaining now equals one of these values.
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The next thing we do is we create a Timer.
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So this timer code you would have found probably from StackOverflow or Googling around,
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but, essentially, it has a bunch of parameters in it.
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So it asks you for "How often do you want the timer to fire?"
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So in our case, because we want our timer to update every second, then we've set that as 1.0,
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so 1.0 seconds. And then we've got a parameter for whether if we want our timer to repeat,
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so we do, we don't want it just to stop after the first second.
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So we've set that as "true."
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And then we've got this parameter code selector. And the selector is a bit of a remnant from the olden
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days where we used to create things using objective c.
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So the way that we use it is we provide a name of a function.
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So it's almost like it calls this function that we put in here every single second every time the timer
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fires.
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Now, when you created this function code updateTimer, you might have gotten an error that has a little white
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dot in it, and it says that selectors come from Objective-C. So in order to expose this method or make
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this method work with Objective-C timers, then you have to add that little annotation, the @objc
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in front.
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So that's all it is.
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And we don't really need to understand how the timer works or how a selector works.
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The goal of the challenge was to get you just comfortable with finding out how to do things through
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searching and through using the five-step method to just make it do what you wanted to do.
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And in later lessons as we get better at Swift and as we learn more programming, then these small things
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will become more and more clear to us.
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So here we have a function called updateTimer which we know will fire every second. In here, we're
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checking to make sure that we've still got time on the clock,
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So seconds remaining is larger than zero.
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And if so, we're going to print the number of seconds that we currently have remaining, and then we're
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going to minus one from it, so that the next time our timer fires, it will be printing a second
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that's one lower from before.
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So this is, essentially, how we've achieved this timer mechanism.
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But if you've been testing it carefully, you'll notice that if you start out pressing one button,
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so the one that should start at 300, and then midway, you change your mind and you press a different button,
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now our timer seems to have sped up. It's actually running down the seconds, almost two seconds in one
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go.
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So it's doubling its speed.
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And if we press another one, then it's going to speed up even more.
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It's now three times as fast as before.
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So what's going on here?
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Well, the reason is because we create this timer, but we never actually cancel it.
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We never stop it.
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So it's the same timer that's running. And every time we press one of the button, we create a new timer
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and we call this method every second.
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So now we're calling this method twice a second or three times a second depending on how many times
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we've pressed this hardness selected IBAction.
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So how can we prevent this from happening?
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Well, we could create a variable code timer and set it equal to a Timer. And then down here, we assign
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that timer variable a new piece of data which is the actual scheduledTimer. But every single time that
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the button, the Soft, Medium, or Hard buttons get pressed, we actually invalidate our timer.
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So we stop it and cancel it, so that the next time we create a timer, we actually create a brand new one.
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So now if we run our app and we press one of the buttons, you can see it's counting down one second every
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second of the clock.
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And if I change to a different button, it will still count down once per second, instead of speeding up
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like before.
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Now, here's another challenge for you.
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How can we change the label that's currently on our Main.storyboard?
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So the one here where it says, "How do you like your eggs?"
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How can we make it say done once our timer is up?
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So in order to make it easier to test your code, I recommend changing these eggTimes from 300 seconds
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where you have to wait a whole 5 minutes back down to 3, and 4, and 7. This way when you're
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testing it,
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it's much, much faster.
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Pause the video and try to see if you can make the code change the title label to make it say "Done"
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once our timer is up?
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All right, first things first, we need an outlet to be able to change this label. So right up here,
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let's control, drag it over, and I'm going to call it just a titleLabel, and hit enter.
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So now we're actually able to change our title label and we're gonna do it right here.
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So here we have an "if" statement that checks if the secondsRemaining is greater than zero,
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then continue taking along.
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But if the secondsRemaining was, in fact, equal to zero, so not greater than zero,
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well, then we could capture that with an "else" statement.
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So we add the "else" statement.
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And when this happens, we first invalidate our timer,
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so we run our timer.invalidate again to stop the timer from continuing to tick every second.
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And plus on top of that, we tap into our titleLabel.text property,
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and we make it say "DONE!"
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So now if we run our app and I'm going to select the Soft button and you'll see my timer goes 3,2, 1, DONE!
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So that's exactly what we wanted.
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All right.
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So now that we've got our timer functionality down, the next step is to add a progress bar.
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So that's what we're gonna do in the next lesson.
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So I'll see you there.