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An alert dialog shows a message to a user, and importantly, requires the user to dismiss it somehow before continuing. This is perfect when we want to make sure the user sees a message about an error.
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Let us start by talking a bit about
the try-catch block we have in our code.
0:00
The idea here is that if something bad
happens in our app, the Java runtime
0:05
system will kind of raise a little
flag that says something is wrong.
0:09
If we are on the lookout for these flags,
we can handle them appropriately and
0:13
save our users from a crash or
bad experience.
0:17
The act of raising that little flag
is called throwing an exception
0:21
when we must catch them
in code in our app.
0:25
A lot of methods we use
throw exceptions like these.
0:28
The response.isSuccesful()
method is one example.
0:31
It throws a specific type of
exception called an IO exception.
0:35
Which stands for input output exception.
0:39
Specific exceptions
like this are typically
0:43
subclasses of a base
class called exception.
0:46
What can we do about them?
0:49
We need to wrap our code in
something called a try-catch block,
0:51
like we have here.
0:54
Our code then is essentially saying, try
to check if the response is successful.
0:59
If so, do something.
1:04
In this case,
output to the log the forecast data.
1:06
If it fails with an IOException, run
this other code to handle the exception.
1:09
Otherwise, we just proceed as normal.
1:15
In this specific case,
we are just logging the exception.
1:17
But we could take other
appropriate action as well.
1:21
Next, let's talk about how to handle the
case where the response is not successful.
1:25
We want to add an else block here.
1:29
Down under the if,
I like to drop this down.
1:32
That's just a matter of personal taste.
1:39
So inside here let's Log.v(TAG).
1:42
It would probably be helpful to
know what the response looks like.
1:46
Response.body().string.
1:52
Now to make our code follow the dry
principle of, don't repeat yourself.
1:57
Let's move the log statement up here
to the top of the try statement.
2:02
We can get rid of that one.
2:18
Now it would be great to alert
the user about the error somehow.
2:22
After all, they won't see
the log messages in the app.
2:26
Let's create a new method inside
our else statement to do just that.
2:30
Call it alertUserAboutError.
2:34
You can come over here now.
2:41
Hit Alt + Enter.
2:43
For the quick fix pop-up,
we want to create a new method or
2:48
alertUserAboutError.
2:52
And we wanna create it
here in MainActivity,
2:53
not in this anonymous inner class.
2:56
We want the main activity.
2:57
Scroll up a little bit.
3:01
Inside our new method,
3:03
we want to do something to visually alert
the user that an error has occurred.
3:05
We could certainly use
a toast as we've seen before.
3:09
But the issue with toast method is
that they only stay on the screen for
3:12
a short period of time.
3:16
If we want to make sure
the user sees a message,
3:17
we should use something that requires
them to confirm or dismiss it.
3:20
Android provides a nice way
to do this with dialogues.
3:24
Let's go to the Android docs and
check out the documentation for dialogues.
3:27
Dialogs pop up over the activity and
ask the user to do something.
3:40
You're probably familiar
with them in other apps, and
3:45
this is a great use for them.
3:47
They can be simple or quite complex.
3:49
We'll just build a simple one for our
StoreMe app that has an error message and
3:52
an OK button.
3:55
We scroll down on this page a little bit
3:57
We read that we should use a dialog
fragment as a container for our dialogs.
4:02
Now, it is kind of a lot of code for
4:06
what appears in the app
as a pretty simple thing.
4:09
The good news though is that once
you have this example working,
4:12
you'll have code you can easily reuse and
adapt in the future.
4:15
Let's head back to Android Studio into
our code and add a dialog to our app.
4:19
So first, we'll need a new class for
4:24
that dialog fragment,
as mentioned in the documentation.
4:25
We can do that here in the Project pane.
4:29
Select Java, To New Java Class.
4:31
We'll call it AlertDialogFragment.
4:38
And for the super class, we will want to
4:47
put in android.app.DialogFragment.
4:52
Everything else is okay. Fragments
4:57
are similar to activities and
are very useful in certain situations.
5:02
We'll cover fragments in more
depth in future projects.
5:06
For now, we need to override one
key method from DialogFragment.
5:09
Type onCreateDialog and
hit Enter for auto-complete.
5:14
The method will be called
when we create the dialog.
5:19
We will do this from our
activity in a moment.
5:22
We need to add code here
to configure the dialog.
5:26
To do that, we will use a special
dialog class called AlertDialog.
5:29
So we can delete this line here,
And replace it with the following.
5:34
AlertDialog.Builder.
5:40
Builder, option enter for inputs.
5:46
And we want that first one there.
5:49
Not the support.
5:52
We want a new AlertDialog.Builder.
5:54
Now we need to pass in the context.
5:57
Normally we would use this or
5:59
activity.this to refer to the current
context which has been the activity.
6:02
However, now we're in a different class so
what do we use for our context?
6:08
Fortunately, the DialogFragment
class that we're extending
6:13
has a useful method to get the activity
where this DialogFragment was created.
6:17
We call it with getActivity which will?
6:23
Yeah, you guessed it, give us
the activity and the context we need.
6:26
So we can put in, getActivity.
6:31
Let's actually make it into a variable
as well, that will be useful shortly.
6:35
So context context,
do our imports, getActivity().
6:43
And then we can pass
in context down here.
6:50
Notice that our data type
is alertDialog.builder.
6:58
Builder is a nested class inside
the AlertDialog class.
7:02
As a quick side note here, the reasons for
7:06
this have to do with a software design
pattern called the factory method pattern.
7:08
I've put links in the teacher's notes for
further reading on this.
7:13
Now is a great time for a quick break.
7:16
When we get back,
we'll setup this alert dialogue.
7:18
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