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Accessor Access Modifiers
5:57Property accessors can also be protected.
Let's create one more new
type of invader together.
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The invader class has another property
that we haven't made overridable yet,
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the health property.
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Let's do that now by adding
the virtual keyword here.
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Now, we can have different
types of invaders
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that have different
levels of initial health.
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Let's create a StrongInvader
class in StrongInvader.cs.
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To save on typing, I'm going to copy and
paste FastInvader and make changes to it.
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We'll replace fast with strong.
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And delete the StepSize property.
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Let's copy the health
property from invader.
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And we'll need to change
this virtual to override.
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Now that we have a StrongInvader,
let's add it to the level.
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The invaders in this level are shaping
up to be quite formidable.
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We'd better make some enhanced
towers to combat them.
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Let's make sure everything
compiles first though.
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Oh-oh, we got a compiler error.
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It says,
TreehouseDefense.StrongInvader.Health
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is marked as an override, but no
accessible set accessor found to override.
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I think I know what happened.
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You see, the setter of
the health property is private.
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This means we can't access
it from strong invader.
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Getters and setters of properties can
have their own access modifiers, so
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long as they are more restrictive than
the accessibility of the property they
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belong to.
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In invader.cs, we can change
private here to protected and
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this will give StrongInvader
access to health property setter.
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Health is a public property.
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So, by default, its getter and
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setter are both public unless
we change their accessibility.
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If health was a protected property, we
wouldn't need to have the protected access
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modifier here, because both the getter and
the setter would already be protected.
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We want health to be public,
but we still don't want classes
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other than sub classes to be able
to change the health directly.
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So we want the setter to be protected.
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Let's compile again to
see if this fix things.
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They have another compiler error.
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TreehouseDefense.StrongInvader.Health.set
cannot
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change access modifier when
overriding protected inherited
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member
TreehouseDefense.Invader.Health.set.
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I think I know what happened here, too.
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I changed the setter to
protected in invader, but
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I didn't change it in StrongInvader.
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The access modifiers of
overridden properties
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must match the property of the override,
so this setter must also be protected.
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Let's compile again to
see if this fix things.
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All good.
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All is well.
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We just learned that sub classes can't
change the interface to the properties and
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methods they override.
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If we further sub classed StrongInvader,
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the accessibility of the members of
that class would have to match these.
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Meaning, the health property would need
to be public and its setter, protected.
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We can't change it in sub classes.
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We've got lots of types of invaders now,
let's make some more types of towers, too.
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We can make towers that have
different ranges, power and accuracy.
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Right now range, power and
accuracy are private constant fields.
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So, we want to change these two
protected virtual properties so
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they can be overridden in sub classes.
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Let's go ahead and do that right now.
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So change this to protected and
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virtual, and
get rid of the const modifier.
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And because it's a property and
it's protected, the common convention
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is to start protected member
names with an uppercase letter.
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And we'll make it a read only property
by just giving it a getter, and
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it's initialized to one.
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Let's do this with the rest of the fields.
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We changed the names of these members.
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So, we'll also need to fix the names
where these properties are used.
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So we'll change this underscore our range
to capital our range, underscore A,
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accuracy to capital A, Accuracy, and
underscore P, power, to capital P, Power.
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Just make sure that we've got everything.
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All right, that looks good.
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Now, we can create new types of towers.
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We can make new types of towers that
have more power, longer ranges,
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or different accuracies.
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But by now,
you already know how to do this.
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Why don't you go ahead and
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create some sub classes of tower on
your own that override these properties.
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I suggest making a powerful
tower with more power,
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a sniper tower with higher accuracy, and
a long range tower with a longer range.
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You can even make a super tower
with more than one enhancement.
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I won't walk through creating
these new tower types here,
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because you know everything you
need to know to make them yourself.
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I've included the code for
sniper tower, powerful tower, and
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long-range tower in the download for
this video.
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I encourage you to try to create at least
one new type of tower before moving on.
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