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So our app now at least has some functionality
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and when we pressed the Roll button, things actually happen on screen.
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Well, at least until it crashes when we run out of images to display.
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So there's a couple of things I want to do here.
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First, I want to simplify the code a little bit because we no longer need anything to happen when the
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view loads up, then we no longer have a need for this block of code. So we can simply go ahead and delete
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it.
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Now, the next thing I want to show you is that while we have this very clear way of writing leftDiceNumber
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equals the current value of leftDiceNumber + 1 is actually a far more efficient way of writing
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this.
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And because in programming, we often need to increase the value of variables by 1 or by 2,
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this is why there's prebuilt ways of making this easier.
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So in Swift, we could simply write += 1, and that will take the current value of leftDiceNumber
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add 1 to it, and then set it to the value of that Variable.
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But if you look at this straight away without the context, then it can be a little bit confusing as to
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what's going on.
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So I'll leave you to be the judge of which version you prefer. And remember that it's not just plus that
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you can do this with, you can do minus or multiply or divide, and it will basically do the calculation
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as if you're taking the current value dividing it by the value after equal sign, and then assigning
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it as the value inside the variable. I'm going to leave that as a += 1
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and I'm going to change this to -= 1. And if you run your app, you'll see that it works exactly
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the same way as before.
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Nothing has changed other than the fact that we've made our code a lot shorter.
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Now, there's gains and other places as well
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and we'll talk about them when we come across them.
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But the main goal right now is to make our app not crash when it gets to the end of the Array and the
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other thing to think about is that it's not really a dice app if it just goes through all the numbers
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in sequence, right?
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That's not random.
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So how do we get some random numbers showing up instead?
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Well, in swift you can generate a random number by simply writing Int.
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So this is the data type that refers to a integer which is also known as a whole number,
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so no decimal places.
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And then if we write a .random, then we can tap into a range of numbers. So we can say give us a random
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whole number from 1 to 10.
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And that's what that three dots do.
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It's specifying a range from 1 until 10.
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And when this line of code runs, it will look at the range and generate a random number between 1 and
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10.
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So inclusive of both 1 and 10.
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Now, if I go ahead and simply wrap a print statement around that and hit run, and when I press the Roll
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button, you can see that we get a bunch of random numbers being printed. Well, at least until our app crashes
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because of this line again.
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So let's put two and two together.
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What we need is a random number here to be able to pick out a random image from our Array.
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So we have six array images and they start counting from zero.
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So this one is at position zero until position 5.
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So we basically need this to be a random number between 0 and 5,
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right?
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So maybe at one point when we press the Roll button, it'll generate 4.
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But the next time, it'll be 2, and then the next time, it'll be zero.
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But it has to be random.
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So let's transplant this code here inside the print statement which we already know can generate us
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random numbers between 1 and 10,
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but let's replace that range and make it between 0 and 5
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and I'm going to do the same for the bottom as well.
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I'm going to delete that print statement and let's run our code again. Now, if I press the Roll button,
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you can see that I'm getting completely random numbers showing up. And there is no end to this app anymore
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because it's just going to stay within the limits of our range here that we've specified between zero
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and 5.
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It's never going to go to 6 or 7 or 8 which does not correspond to an image in our Array.
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We can no longer crash our app which is wonderful.
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So we've made our app behave more like a real dice.
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And in addition, we can now delete this leftDiceNumber and rightDiceNumber both where we are using
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it as well as where we're creating it.
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So our code is now even simpler.
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Now, this is what we call refactoring in programming where we take our code and try to make it simpler
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and make sure that we don't have any code that is repeating or unnecessary. We can take this even further
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because look right here, we have that same Array that's being used in both places.
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So why don't we, instead, just create a reference to it, give it a name and use the name every time, instead
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of having to create this Array. And even though Xcode makes this display really nicely and show us the
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images, as soon as there's some issue in your code, let's say, we commented out this code, you can see what's
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behind the scenes is actually quite complex.
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There's something called an imageLiteral being created from a resourceName,
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and this makes our code quite long and quite wordy. So it'd be great if we didn't have this duplication.
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So what if we could create a variable that holds this Array as the Variable's value and then we can refer
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to that Variable when we need to use this Array. Just above these two lines,
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I'm going to create a new Variable which I'll call diceArray and I'm going to set it to equal this
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array right here,
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so I'm making sure I'm copying in all the square brackets and I'm going to paste it in here.
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Now, in Swift, it's really important to make sure that you have consistent or symmetric amount of space
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on either side of the equal sign.
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So for example, you could have no space, either side of the equal sign, or you could have one space. But
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try to avoid it where you have an asymmetric situation like this because you'll get an error from
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Xcode.
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Now, when you see a warning or a error,
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so the yellow triangles are the warnings which says, "Hey, I think there might be something wrong, but you
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might know better,
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so you can continue," or the red stop signs say, "Stop.
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There is an error and you must fix it if you want to run this app."
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And when these symbols have a little white dot in it, it means that Xcode thinks that it knows the solution
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to this problem.
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So if you click on it, you can see a Fix button, and you can see what it's going to try and do when you
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click on this Fix button.
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So in this case, it's going to insert a space after the equals sign.
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Let's click Fix and it automatically fixes that for us.
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Now, it's really important that when you click on the Fix button, you know exactly what it's trying to
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do and why it's doing it,
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so you understand what's going on before you just let Xcode fix everything because Xcode is still
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quite far from Skynet.
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It thinks it's very clever, but it's actually not.
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So there are many cases where it thinks it knows the solution, but actually it just messes up your code.
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You are the human programmer. You are the one telling the computer what to do. Make sure that you know
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exactly what Xcode is trying to fix before you click on it.
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Now, that we've got this dice array here, I'm going to ignore this warning for now and then we'll come
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back to it a little bit later on.
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But the point is we now have a reference to our Array and we can reduce the duplication right here.
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So instead of actually providing the Array, we can simply refer to the Array,
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and if I type in its name down here, then when this line of code runs, it's gonna go and look for
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this diceArray which lives right here,
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and then it's going to try and pull out a random item from it between 0 and 5.
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Now on the next line, I can do exactly the same thing. So use the reference to diceArray,
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and if we run our app right now, you'll see that nothing has changed.
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We still have our dice rolling functionality and it rolls any random dice between 1 and 6.
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Now, let's come back and address this warning from Xcode.
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It says, the variable dice array,
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this one, was never mutated consider changing to a 'let'
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constant.
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What is this trying to tell us?
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Well, here we've created a variable which is created using the var keyword
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and we've basically given this collection of items a name, so that we can refer to it later on.
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But given that it's a variable, surely, we would want to vary it at some point,
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right?
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But at no point in our code do we ever change the value of dice array,
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it's not like right at the end,
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we tap into the diceArray and we set it equal to a different set of image literals.
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So maybe the diceArray is now composed of the logo and the background image.
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In this case, we've created the Variable and then, subsequently, we vary the contents of that Variable,
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so we've changed the values that's held inside.
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Well, this is what a Variable is used for,
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and it's really common. Well, say, if you had a score, right, where the user starts out with a score of
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zero,
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but then, later on, we add one to it, so that we increase their score.
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Well, this is where we're varying the Variable. But in our case, we don't actually need to vary the
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diceArray because that's all the images we have.
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We don't have any other images. So why do we need to change it?
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Well, we don't.
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So that's why Xcode is telling us consider changing it to a 'let'
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constant.
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And, again, this warning here has a white circle in it.
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So it means Xcode thinks it knows how to fix this.
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Let's click on it and see its suggestion.
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It says, "Why don't you replace the 'var' keyword with a 'let' keyword to turn it into a constant.?"
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So let's click on Fix.
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And now all our warnings go away.
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And if we run up again, it will work exactly the same as before.
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But all that we've done is instead of allowing this to be changed,
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this is now a constant.
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So if I decided that diceArray was going to have some other images inside, I don't' know, let's say, if we deleted
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some of these values, then you'll see that it'll actually give us an error.
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You can't assign to this value. diceArray is a constant.
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And it tells us that if you do want to change this Array and you want to change its values, well, then
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you have to change that 'let' back to a 'var,' and that's what it's automatic fix does.
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So we don't want that.
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We're never going to change the Array, so we can keep it as a 'let' constant.
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We've seen that we can generate a random whole number between the range of 0 to 5 and this is a really
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heavily used bit of code.
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Whenever you're programming anything that needs some randomness, say, for example, a game,
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but in our case, if we just wanted a random item out of our diceArray, there's actually an even simpler
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way of doing it.
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We can delete this and simply write .randomElement and that will do exactly the same as this.
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It will look through this Array, see how many items there are inside, and then give us a random element.
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So if you wanted the ultimate succinct code, then it would probably look something like this where you're
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picking a random element for each of these diceImageViews. But if you find it easier to see what's
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going on and the practice using this random generator, then you might want to keep your code like this.
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The choice is yours. But I recommend that at this point, you take a moment to write some comments in the
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code to tell your future self what each of these lines of code that you've written does, so that when
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you come back to it, when you review it, you'll be able to understand quickly at a glance.
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So pause a video and have a think about some of the new things you've learned in this lesson and write
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some notes on those things. In the next lesson,
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we're going to be doing another deep dive into randomization in Swift, as well as the range operator
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in Swift,
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and look at the difference between the 'let' and the 'var' and when you would use each.
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So if you already know about all those topics, then feel free to skip ahead.
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But if you want to learn more, then have a look at the next video.