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In this video, we'll review the solution to the second and final challenge.
DisplayText Computed Property
Here's what the Album DisplayText property looks like rewritten as an expression-bodied property before adding the OnLoanDisplayText computed property to the MediaType base class.
public string DisplayText => "Album: " + Title + " by " + Artist + (OnLoan ? !string.IsNullOrEmpty(Loanee) ? " (Currently on loan to " + Loanee + ")" : " (Currently on loan)" : "");
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How did you do?
0:00
Let's take a look at my solution.
0:01
In each media type subclass,
0:03
I replaced the GetDisplayText method
with a DisplayText computed property.
0:05
First, the Album class.
0:10
Like I did in the walk through of my
solution for the first challenge,
0:15
I'll show an example of both the regular
and expression body property syntax.
0:19
I started with defining the computed
property using regular property syntax.
0:24
First, I stubbed out the property and
its getter.
0:33
Remember, we're creating a read-only
property whose value is computed using
0:50
other properties.
0:54
So we only need to define a getter.
0:56
For the properties getter implementation,
I cut and
0:59
pasted the GetDisplayText method
body into the body of the getter.
1:02
I'll select that code and
press Tab to fix the indentation.
1:15
And let's go ahead and remove what's
left of the GetDisplayText method,
1:19
as it's no longer needed.
1:23
And that completed my
DisplayText computed property.
1:30
To convert this property to an expression
body property, we need to rewrite
1:35
the code and the getter as a single
expression or a single line of code.
1:39
While it's possible to do, the resulting
code would not be very readable, so
1:44
I'll hold off on showing that example.
1:48
If you want to see what it'd look like,
see the teacher's notes.
1:50
But while I was working on converting
the GetDisplayText method to a computed
1:55
property, I noticed an opportunity
to improve its implementation.
1:59
This code here related to loading media
library items is repeated in both
2:09
the Book and Movie classes.
2:14
So I move this code into
the MediaType base class.
2:17
To start, I added
2:23
an OnLoanDisplayText
2:27
computed property.
2:32
Then I copied and
pasted the repeated code into the getter.
2:48
At this point, I had a little bit
of clean up to do on this code.
3:01
Instead of impending onto the text
variable, which is no longer defined
3:10
in this code block,
I just returned these string literals.
3:14
And I added an else statement and returned
an empty string if the item isn't online.
3:24
Then I switch back to the Album class and
updated the DisplayText Computed property.
3:41
We can now remove all of this code.
3:56
And we can replace our text
variable with the return keyword.
4:05
And at the end of this line, we can
append the OnLoanDisplayText property.
4:12
Isn't that code easier to read and
understand?
4:22
After that change,
4:26
it was easy to update the property
to an expression body property.
4:27
After the DisplayText
property name I added =>,
4:32
which is known as a fat arrow, and
4:37
then removed everything up
to the Album string literal.
4:40
And after the OnLoanDisplayText
property and the semicolon,
4:52
I removed the last two
closing curly braces.
4:56
The line of code is a little bit long,
so I'm gonna put my
4:58
right before the album string literal and
start a new line.
5:03
And there, that's our completed
expression body property.
5:09
To update the other MediaType subclasses,
5:14
I copied and pasted the expression body
property to the Book and Movie classes.
5:17
We need to change Album,
here, to Book, and
5:29
this Artist property to Author.
5:33
Then we can remove
the GetDisplayText method.
5:37
Then the Movie class,
5:45
Paste from the clipboard,
Change this Album string to Movie.
5:51
And replace the Artist property,
here, with Director, and
5:59
remove the GetDisplayText method.
6:03
For the bonus challenge,
I opened the MediaLibrary class file,
6:12
And I stubbed out a number of items
expression body computed property.
6:18
Public, so
it's accessible from outside of the class.
6:26
Int for its data type.
6:31
Then the name of the property,
NumberOfItems.
6:33
Then an = and a >,
otherwise know as a fat error,
6:39
then I return the length
of the items array.
6:44
So _items.link.
6:48
Moving on to the Program.cs file.
6:54
Scrolling down to the Display method,
I replaced all the calls to
6:59
the GetDisplayText method with
the DisplayText property.
7:03
And I added a call to
the Console.WriteLine
7:20
method in order to test
the MediaLibrary NumberOfItems property.
7:26
And lastly, I compiled and
ran my program in order to test my changes
7:49
Let's make one small change to make
this output a little bit more readable.
8:12
So Console.WriteLine, and
then let's add a string literal here,
8:19
# of items,
followed by a colon and a space.
8:25
I'll save the file,
8:29
Compile and run my program again.
8:37
There, that makes it
a little bit more readable.
8:42
So here's the number of items
in our media library, and
8:44
then here is the rest
of the expected output.
8:48
Congrats on completing
this practice session.
8:52
Be sure to check out the next session
in the series after you've completed
8:54
the six and
final stage in the C# objects course.
8:59
Thanks for practicing with me and
we'll see you next time.
9:02
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