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Intents can also carry data! In this video we will see how to put "extra" data in an Intent that can be retrieved by whatever receives the Intent.
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We have the user's name here in main
activity but it's stuck in there.
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We can't access it yet
in our new story activity.
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If you are relatively new to programming
you might think we can add some sort of
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member variable up here and
share it somehow.
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But that would create a type
coupling between two activities that
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should not exist.
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Such type integrations like that
cause problems down the road
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as systems grow in complexity.
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Our best solution is to pass
the data along somehow.
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This functionality is provided in
the intent object we are using to start
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the new activity.
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The actual intent object gets
passed to the new activity.
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So if we attach data to it, we can
then access that data in the activity,
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where the intent ends up.
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Intents can hold all sorts of data,
called extras.
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We put them into the intent using
one of its many put methods.
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Here, let's try it.
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Let's go back to our
new start story method.
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And before we call start activity,
let's add a new line and
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type intent dot and start typing put,
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and we can see all of the different
methods here available to us.
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We attach data to an intent as a key value
pair which is very common in programming.
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The key is a string name so you can see
that as the first parameter here, and
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we use that name to reference the data
that we attach as the second parameter.
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So with that key we can then pull
out the data in the other activity.
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We're going to pass in the name
variable which is a string, so
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we want the put extra that takes a string
key and attaches a string value like this.
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You don't have to select that one,
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it will get selected automatically
based on the parameters we pass in.
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For the key, let's call this name.
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And then for the value,
we can use the name variable, but wait,
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our name variable is out of scope.
1:30
Now, it's not giving us an error here, but
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we need to pass in the name that we're
setting up here in the onClick method.
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You're hopefully familiar with
variable scope from Java basics or
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other programming.
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But, if not,
you need to know that variables only exist
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within the blocks of code
where they are defined.
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That's the scope of the variable.
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So because the name variable is declared
up here inside the onClick method,
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it's only available in these lines of code
here unless we pass it out somewhere else.
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So to make it available in this new
method down here, this new block of code,
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we need to either pass it as a parameter
to the startStory method, or we could make
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it a class level member variable that's
available anywhere inside this class.
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That's fine, but it's usually better to
constrain the scope where we need it.
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So let's pass it as a parameter.
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Member variables should ideally be
the properties of the object and
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the name here isn't really
a property of this activity.
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It's going to be part of our story and we
are just passing it along via the intent.
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So let's add a new parameter here.
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In our definition we'll say, String name,
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and now we can add the name variable
here in the parentheses above.
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If you're wondering why we can use
the same name for the variable here and
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in the parameter down here,
that's again because of the scope.
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These are two totally different scopes so
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the variables have nothing
to do with each other.
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They can thus be named the same because
once we're out of this method up here,
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this variable will cease to exist.
2:51
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