- Accessing Views in Code: Declaring Variables 5:20
- Accessing Views in Code: Assigning Variables 6:24
- Initializing a Button 1 objective
- Making a Button Do Something 4:35
- Adding the OnClick Method 2:36
- Android Programming Basics 5 questions
- Generating a Random Number 4:08
- Choosing a Random Fact 4:52
- Using the Random Class 4 objectives
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Generating a Random Number
4:08The heart of the logic behind our Fun Facts app is randomly selecting a fact. In this video we'll learn how to create and use objects of Java's Random class to generate a random number in a given range!
Back in our funfacts activity class,
we've just finished setting it up so
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that when we tap on our button,
this OnClickListener detects that tab.
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And then runs the code we see
here in this onClick method.
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Right now the app is pretty boring.
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It just shows this one fact over and
over each time we hit the button.
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Let's take a look at this code and
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talk about how we can change
it to be more exciting.
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We start with a string variable named
fact, which holds the text of our fact.
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But for now, it's hardcoded as,
Ostriches can run faster than horses.
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To make this dynamic,
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we need to change the fact variable
based on some sort of randomization.
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Let's start by setting our fact variable
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equal to an empty string by deleting
everything between the quotation marks.
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We have to leave our fact
variable equal to something, or
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else we'll get an error when
we try to set the text.
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Then, let's add some comments to give us
an outline of what we hope to accomplish.
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Let's add a line above our fact variable
and say, Randomly select a fact.
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Then let's add two lines below our fact
variable and add a comment that says,
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Update the screen with our new fact.
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And that's all there really
is to the heart of our app.
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We randomly choose a fact, and
then we display it to the user.
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All right, let's start by creating a new
random object named Random Generator.
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Random is a class provided by Java
itself that makes it easy for
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us to generate all sorts
of random numbers.
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Let's add a new line up here and
then type Random, and
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call it randomGenerator, = new Random.
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Then let's create a new
integer named randomNumber,
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to store the number we generate.
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And let's set it to = randomGenerator.
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And then right at the top of autocomplete
is the nextInt method we want.
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Now we're generating a random integer.
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But how do we know what
range it's going to be in?
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What if it's a really high number?
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We were only going to have
ten facts in our app.
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But for right now lets pretend we only
have three facts to keep it simple.
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How can we limit our randomNumber
generator to just three choices?
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Luckily, there's another version of the
nextInt method that takes in a parameter
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that tells it how many
numbers to choose from.
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Lets go back between the parentheses and
type a 3.
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Now seems like a good time to stop and
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make sure we have things
working like we want them to.
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Instead of setting our label to the blank
string stored in the fact variable,
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let's quickly test our randomNumber
generator by setting our fact variable
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equal to our random number.
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And we get an error, if we hover over it,
it says Incompatible types.
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The fact variable is looking for
a string, a randomNumber is an int.
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We need a randomNumber to be a string,
an easy way to do this
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is to force a conversion by adding
an int and a string together.
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Let's add + and then an empty string and
viola, the error disappears.
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The + can be used to add numbers together,
but it can also add strings together.
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And when it's between a number and
a string, the string version wins, and
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the number gets automatically converted.
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Since the string we're adding
to our number is empty,
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this ends up just being the string
representation of randomNumber.
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Which is exactly what we want, all right,
let's run this and see what happens.
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And if we click on our button
we see that our text view
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gets updated with different numbers.
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Cool, and it looks like the list of
numbers starts at 0 instead of 1.
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So we get 0, 1, 2 instead of 1, 2, and 3.
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