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Returning a string literal from a controller action method is unusual. An action method typically returns one of the MVC action result types. Let’s see how to do that.
Follow Along
To follow along commiting your changes to this course, you'll need to fork the aspnet-comic-book-gallery repo. Then you can clone, commit, and push your changes to your fork like this:
git clone <your-fork>
cd aspnet-comic-book-gallery
git checkout tags/v2.4 -b using-action-result-types
Additional Learning
For more information on the .NET types used in this video, see these MSDN pages:
-
ActionResult class (from which both
ContentResultandRedirectResultderive) - DateTime Structure
This Stack Overflow question will show you how to disable the Diagnostic Tools in Visual Studio.
Keyboard Shortcuts
-
F12- Go To Definition -
ALT+F12- Peek Definition
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Returning a string literal from
a controller action method is unusual.
0:00
An action method typically returns
one of the Mvc action result types.
0:05
Let's start by replacing our string
literal with a content result object.
0:10
Content result is an action
result type provided by Mvc.
0:15
Just above our existing return statement,
0:19
let's return an instance of
the content result class.
0:22
Since we're no longer returning a string,
0:29
we'll need to change our methods
return type to content result.
0:31
We can use the ContentResult content
property to set our content.
0:37
To do that,
let's add a set of curly braces
0:41
to the right of the ContentResult
constructor call.
0:45
In between the curly braces,
type the property name Content
0:49
followed by an equal
sign in a pair of quotes.
0:53
Then let's cut and
paste our string literal from here
0:57
to there and
remove the extra return statement.
1:03
Let's run our website by pressing F5 and
1:08
verify that everything is
still working correctly.
1:10
Remember even though we replaced our
string literal with a content result
1:13
object, we still expect our detail action
method to return the same content.
1:17
Don't forget we need to browse
to the URL ComicBooks/Detail.
1:23
Great, we [LAUGH] didn't break anything.
1:27
Go ahead and close Chrome.
1:31
Stop the website and
hide the output window.
1:33
Content result is just one of the action
result types that NVC provides.
1:37
Another action result type,
redirect result,
1:41
is used to redirect
the user to another URL.
1:44
Let's add an if statement that
will redirect the user to the home
1:47
page if today is Monday.
1:51
We can use the DateTime.Today static
property to get a date time for today.
1:54
On that object there's
2:01
a DayOfWeek property that we can
use to check if today is Monday.
2:04
To do that we just compare
the property value
2:08
to the DayOfWeek.Monday enumeration value.
2:11
In a later course we'll cover in more
detail how to work with dates and
2:15
times in C#.
2:18
If you'd like to learn more now,
see the teacher's note for
2:20
links to additional resources.
2:23
Okay, inside the if statement,
2:26
let's return a new instance
of the redirect result class.
2:28
In the constructor,
let's pass the string literal /,
2:33
which represents the root of our website.
2:36
Hm.
2:40
There's a problem with our code.
2:40
If we hover our mouse pointer
over the offending code,
2:42
we can see the error message.
2:45
Cannot implicitly convert type
System.Web.Mvc.RedirectResult
2:47
to System.Web.Mvc.ContentResult.
2:53
Looks like the compiler was
unable to implicitly convert
2:57
the redirect result type to our
methods content result type.
3:01
We can try explicitly casting the redirect
result object to content result
3:05
by typing a set of parenthesis
containing the type content result.
3:10
But that doesn't work either.
3:17
Cannot convert type,
RedirectResult to ContentResult.
3:19
To resolve this issue, we need a type that
isn't common to both of our result types.
3:24
Let's go to the definition for
3:30
RedirectResult by putting the cursor
on the constructor and pressing F12.
3:31
Since the RedirectResult
class is part of Mvc and
3:36
we don't have the source
code in our solution,
3:41
Visual Studio will only display the basic
information for the public class members.
3:43
For our purposes,
that will work just fine.
3:48
We can see that the base
class is ActionResult.
3:51
Let's go back to our controller and
3:55
put our cursor on
the ContentResult constructor.
3:56
This time let's hold down
the alt key when pressing F12.
4:00
This allows us to peek the definition
in line with our code.
4:04
If we scroll up a bit in the peek window,
4:08
we can see that the base
class is also ActionResult.
4:10
So redirect result and
content result have a common base class.
4:14
Let's close the peek window and change
our methods return type to ActionResult.
4:19
Problem solved all of the Mvc ActionResult
types share the action result base
4:27
class because of this action result is
almost always used as the return type for
4:32
action methods.
4:37
Regardless of the specific ActionResult
type that is being returned.
4:39
Remember the Mvc Controller base
class that we're inheriting from?
4:44
The Controller base class
provides a number of methods
4:48
that can help simplify our code.
4:51
We can replace our ContentResult object
with a call to the Content method,
4:53
which accepts a string for the content.
4:58
We can also replace our redirect result
object with a call to the Redirect
5:07
method which accepts a string for
the target URL.
5:12
Let's run our website and
test our changes.
5:18
Don't forget to browse
to ComicBooks/Detail.
5:23
Good, we're still seeing our content.
5:29
Next let's stop the website and
update our if statement, so
5:32
that we can test our call
to the Redirect method.
5:35
I'm recording this video on a Tuesday.
5:40
So I'll update the day
of the week to Tuesday.
5:42
Restart the website by pressing F5.
5:48
When Chrome is finished loading,
browse to ComicBooks/detail.
5:50
Excellent, notice here in the address
bar that we've been redirected
5:57
to the root of our website.
6:01
Which is still returning a 404 Error,
go ahead and stop the website.
6:03
If you're using GitHub
let's commit our changes.
6:09
Enter a commit message
of Updated Detail action
6:14
method to use action result types and
click the Commit All button.
6:19
We've done a number of local commits so
6:28
now would be a good time
to sync with remote server.
6:30
Click Sync here in this
confirmation message
6:33
to navigate to the synchronization panel.
6:36
Here's a list of our local commits
in the outgoing commit section.
6:39
Click the Push link to push
these commits to the server.
6:43
Okay, we're making progress.
6:48
But we're still returning a string for
our content.
6:50
It's worth noting that we're not limited
to returning just a plain string.
6:53
We could update our content
result to include HTML Markup.
6:58
But our controller shouldn't be concerned
with the presentation of our content.
7:02
As we discussed in an earlier video,
controllers are coordinators.
7:07
They're responsible for
7:12
coordinating the specific actions
that need to be performed.
7:13
In order to return a response for
that user request.
7:16
Presenting content is a job
better suited for a view.
7:20
So, how do we return a view?
7:25
In the next section,
we'll add our first view.
7:27
See you see then.
7:30
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