- 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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Choosing a Random Fact
4:52It's often helpful to group items together into an array. In this video, we'll create an array of facts. Then we'll use our randomNumber to help us pick a random fact!
We just programmed the heart of our app,
the random number generator.
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Now we need to use that generator
to help us pick a random fact
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on each button click.
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But before we can do that,
we'll need a pool of facts to choose from.
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Let's start by creating
an array to hold our facts.
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Remember, an array is just a container
that holds values of a specific type.
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Let's add two lines to the top
of the onClick method.
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And then type String, facts.
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We now have a new variable called facts,
and
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we've declared it to be an array
of strings, or a string array.
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You can make an array out
of any type of object.
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All you need to do is add square
brackets after the data tag.
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All right, now for
the assignment side of things.
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For the sake of time,
I'm going to paste in the ten facts and
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then we'll go over the syntax.
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You can type these out if you want, but
I've put this code in the teacher's notes
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so you can just copy and
paste as well, let's do it.
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I'll select everything after
the word facts, up to but
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not including the semicolon.
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Then I'll copy this and
paste it between facts and
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the semicolon back in the onClick method.
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And now we can see that one
way to initialize an array
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is with an comma-delimited list
between two curly brackets.
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Now that we have an array
of strings to select from,
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let's use our random number generator
to help us pick one at random.
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Our array has ten elements in it.
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Let's start by changing our
random number generator
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to have a range of 10 instead of 3.
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If we clicked on our button now, we'd
see random numbers ranging from 0 to 9.
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And what else do we have
that ranges from 0 to 9?
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That's right,
the indices of our facts array.
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This first fact about ants is at index 0.
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And this last fact about
mammoths is at index 9.
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So if we want to select a random fact,
we just need to select the fact
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from our facts array that's at the index
of the random number we generated.
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It seems easy enough.
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Let's start by getting rid of what we're
currently setting our fact to, And
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then type facts,
in square brackets, randomNumber,
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to select the fact at
the index of our randomNumber.
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All right, that should do it.
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But before we test our app, there's
a potential bug we should fix first.
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What happens if we add a new
fun fact to the array?
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Can you tell where the code will break?
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I'll add another fact and
then let's talk about it.
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I'll say,
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Treehouse is not actually in a tree.
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Now that we have 11 elements in our array,
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we need to change 10 to 11 down
here in our call to nextInt.
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But if we forget to change it, we'll
never see our new fun fact in the app.
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Wouldn't it be nice if we could somehow
use the number of elements in the array
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as our parameter instead of
a hard-coded number like this?
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Then we wouldn't have to change
it every time that we add or
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remove elements in our array.
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Sure enough, Java has a way for
us to do this.
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Let's delete the number 10 here and
type facts.length.
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This gives us the length
of the facts array,
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which is another way to say
the total number of elements.
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By using this property of the array,
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we will always pass in
the right number of elements.
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This saves us the work of having
to manually change numbers and
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it also protects us from errors.
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For example, if we had deleted an element,
I'll delete this one that I just added,
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But we left this number as 11, then our
app may try to reference an element that
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doesn't exist and it would crash.
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Looks good to me, let's click on
the run button to test our app.
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And then we can tap the button and
we should see some of the new facts.
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And there we go,
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mammoths still walked the earth when
the Great Pyramid was being built.
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And if we keep clicking,
we should eventually see all of our facts,
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very cool.
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Awesome work, don't worry if all these
new Android words aren't sticking yet.
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We've done a lot and
we still have a lot to do.
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But if you stick with it,
I'll explain everything you need to know.
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And if you want to talk about
anything you're stuck on,
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head over to the community for
questions or discussions.
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It's easy to feel
overwhelmed with this stuff.
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But trust me, things will start to
make more sense the more you practice.
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On that note,
why don't you try some more practice?
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