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You have completed Practice Inheritance in C#!
You have completed Practice Inheritance in C#!
Preview
In this video, we'll review the solution to the third challenge and introduce our fourth and final challenge—throwing and catching exceptions.
Instructions
4th Challenge
-
In the MediaType.cs file...
- Throw an exception in the MediaType class constructor if the
titleparameter is set tonullor an empty string. - Set the exception's message to "A media type must have a title."
- Throw an exception in the MediaType class constructor if the
-
In the Program.cs file...
- Throw an exception in the
DetectMediaType()helper method when an unexpected media subtype is encountered. - Set the exception's message to "Unexpected media subtype encountered."
- Wrap the code in the
Main()method in atry/catchstatement. - Define a parameter in the
catchclause in order to get a reference to the caught exception. - Write the exception's
Messageproperty to the console.
- Throw an exception in the
Help
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How do it go with the third challenge?
0:00
Let's walk through my solution.
0:02
In the Program.cs file, I created a static
method named detect media type and
0:04
to find the parameter of
type media type named item.
0:10
I load the method right
below the main method.
0:14
Static void DetectMediaType.
0:21
And for the parameter, it needs to be of
type MediaType, and I'll name it item.
0:27
In the method body, I use the series
of conditional statements and
0:34
the C# is operator to identify which
particular media type subclass the item
0:38
parameter is an instance of.
0:43
So, if item, and then the is operator,
0:45
and then the type that we're testing for,
Album.
0:49
Then a set of curly braces.
0:54
Then, else if item the is operator,
then the Book type.
0:56
A set of curly braces, and
1:05
then another else if item is Movie.
1:08
And a final set of curly braces.
1:14
This series of conditionals will first
check to see if the item parameter is
1:17
an Album.
1:21
And if that's not true, it'll check
to see if the item is a Book, and
1:22
if that's not true,
it'll check to see if the item is a Movie.
1:26
After determining the MediaType
item subclass type,
1:30
I wrote a message to the console
identifying that type.
1:33
So if the item is an Album,
1:37
I wrote Console.WriteLine item.Title,
1:40
+, and then a string literal is in album.
1:48
Copy that to the clipboard,
then paste and paste.
1:54
All of this can stay the same
here because item.Titles what
2:00
we need to output, but
instead of is an album, say is a book.
2:05
Same thing down here for a movie.
2:11
We just need to change this to a movie.
2:15
And save the file.
2:20
Okay, so that completed my
DetectMediaType method implementation,
2:22
then I needed to test my changes.
2:27
To do that, I passed each of my
media type subclass instances into
2:33
a call to the detect media type method.
2:38
First, album1, so, DetectMediaType,
2:42
Then I pass album1 into the method call.
2:49
Let's copy that line of code and
paste it four more times.
2:53
I'll pass album2 into the second call.
2:57
Album3 into the third,
and then the fourth,
3:01
will get book and
the fifth method call will get movie.
3:05
And lastly, I save the file, and
I complied, and ran my program.
3:12
And here, we can see each MediaType
item subtype written to the console.
3:23
Great work so far.
3:29
Now, let's take a look at a couple
of shortcomings in our program.
3:30
First, let's see what
happens if we pass null, or
3:35
an empty string as the argument for
a media types title parameter.
3:38
Just after album3 here,
I'll create a fourth album.
3:45
So var, album4 = new Album,
and for the title,
3:48
I'll pass null instead of a value,
then for
3:53
the artist name I'll say, Some Artist.
3:57
Then I'll create a fifth album, so album5,
4:04
= new Album, and this time,
I'll pass an empty string.
4:10
And for the artist,
I'll use Some Artist again.
4:16
Let's save the file, and
compile, and run our program.
4:20
Looks like I forgot to call get
display text on album4 and album5.
4:28
The compiler is telling us that we
assigned a value to those variable but
4:34
we never used them.
4:38
So let's fix that problem, Right here.
4:40
Let's copy that line to the clipboard and
paste it twice.
4:44
Then change album3 to album4,
and album3 here to album5.
4:48
Save the file, And compile,
and run the program.
4:53
And right here in the console, we can see
that our program happily allows the null,
5:07
or empty string value in
attempts to write the album's not
5:12
existent title to the console.
5:15
Let's look at another short coming.
5:17
In the detect MediaType method, let's
comment out the last else if statement.
5:19
Then save, and compile,
and run our changes.
5:29
We can see here that the three
albums were identified.
5:37
And the book, but there's nothing
displaying whatsoever for the movie.
5:41
This tells us,
that the detect MediaType methods silently
5:45
fails to detect the media type for
the movie subclass instance.
5:48
Ideally, the program would make it more
apparent when it encounters either of
5:52
these situations, with a fourth and
last challenge in this practice session.
5:56
Let's update our program to handle both
of these unexpected situations in a more
6:01
robust manner.
6:06
In the MediaType.cs file,
throw an exception in the MediaType class
6:11
constructor if the title parameter
is set to null or an empty string.
6:16
Set the exceptions message to,
A media type must have a title.
6:21
In the Program.cs file, throw an exception
in the DetectMediaType helper
6:25
method when an unexpected
media type is encountered.
6:30
Set the exception's message to
Unexpected media subtype encountered.
6:34
Then, to finish this challenge up,
6:39
wrap the code in the Main method
in a try/catch statement.
6:41
Define a parameter in the catch clause,
in order to get a reference to the caught
6:45
exception, write the exception's
Message property to the console.
6:49
And that's it for the fourth challenge.
6:53
See you in a bit.
6:55
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