In this slide sow we’ll cover some of my musings of some things about Flutter and Dart that your mother never told you as you grew up, but I ran across as I started developing apps. We will cover Functions, Parameters, Exceptions, Futures, Global Variables, Combination Widgets, Custom Widgets

1. Welcome to GDG Bronx
Flutter Study Jam 1

2. Who am I?
Peter Birdsall
presenting …

3. Birds all Flutter
Start building a tool belt.

4. Building a Flutter Tool Belt.

5. Functions and
Methods
Make your reusable methods common as function.
You can just then call it and import them into your
current dart file via Option+Enter
You used to have to type out the import, what a pain!

6. Method Signatures
Dart method signatures are not polymorphic.
So, only a single Signature But, there are options.

7. Method Parameter
Defaults
By default all parameters are positional.
A missing parameter can cause a run-time
exception! OH MY!

8. Making Parameters
Required
Annotation to the rescue.
@required
Makes a constructor parameter to be required via
the IDE.
YourMethodConstructor(
this.key,
@required this.child
…

9. Parameter Options
There are two options, besides the defaults that you
can apply to parameters.
Optional Parameters - ‘[…]’
Named Parameters - ‘{…}’
Surrounding all or a series of your parameters with
braces ‘{}’ makes them named.
Surrounding all or a series of your parameters with
brackets ‘[]’ makes them optional.
-

10. Mutually Exclusive
Named and Optional parameters can not be used on
the same parameter(s).
{Named parameters should occur first} and then
[Optional parameters following] if you are going to
use both.

11. Named Parameters
Named parameters are NOT positional.
Helps make your code more readable.
A common example of Named parameters are in all
of the Widgets supplied by Flutter. So if you used
Flutter your already familiar with them.

12. Optional and Named
Parameters can be Omitted
This can cause a run-time exception and crash the
app.
OH NO! OH NO! OH NO!

13. Luckily, there are options
for your Parameter options.
Both Optional and Named parameters can be
assigned default values
YourMethodConstructor({
this.myString = “Default Value”}

14. Consider your Dart code.
Exceptions can crash your app.
try {
resBody = json.decode(res.body);
} catch (Exception) {
debugPrint(“Exception $Exception”
}

15. Common Exceptions
FormatException - when a variable doesn’t have the
expected format.
IntegerDivisionByZeroException - oops.
IOException - when a basic Input/Output error
occurs.
Timeout - when a timeout occurs on an async result.

16. Try Dart’s ‘try’
try {
// code that might have an exception
} on Exception1
//excepton1 code
} catch Exception2 {
//excepton2 code
} finally {
//code that should always execute
}

17. What’s in your Future?
A Dart ‘Future’ helps asynchronous code feel more
synchronous. It pretty easy.

18. Two things for Futures
A method calling a future needs be defined as
‘async’ and it returns a ‘Future’ object.
YourMethod() async {…}
Your code that executes an asynchronous function
must be prefaced by ‘await’.
SharedPreferences preferences = await
SharedPreferences.getInstance();

19. Future processing
An async method always returns a ‘Future’.
A Future with it’s <generic> place holder is initially
created on the call to the ‘await’ method.
Upon completion the Future it’s <generic> type is
returned as Future<T>, or an error if there’s an issue.

20. The Future is always the
Future, or is it ???
So, you’ve gotten a Future back from your
asynchronous process.
BUT!, I don’t want a Future, I want just the <generic>
or <T>
you can use the ‘.then’
YourAsyncMethod.then((result) {…})

21. A Future non-Future
example, in the Present?
getUserName.then((userName) { String
myUserName = userName;})
getUserName() async {
SharedPreferences = await
SharedPreferences.getInstance();
String userName = preferences.getString(“User”);
return userName;
}

22. Global variables
Sharing a variable.
Typically the first thing you hear about is an
InheritedWidget for sharing state to child Widgets,
but this can affect re-drawing of your screen.
How to I share a variable across different screens?

23. Global variables
- - - 3 Steps - - -
1. Define a library file in Dart, say globals.dart and
add your variables to it.
library global.globals;
bool isTrueGlobalBoolean = false;
2. In your Dart files where you want to use the
‘isTrueGlobalBoolean’ global variable, import it into
your file.
import ‘package:youapp/youdirectory/
globals.dart’ as globals;

24. Global variables
3rd / Last Step
3. Then you can use the isTrueGlobalBoolean
variable as needed:
print(“${globals.isTrueGlobalBoolean}”);
globals.isTrueGlobalBoolean = true;

25. Other suggestions
Combine a large set of widgets into a separate;
either Stateful or Stateless custom combined
Widgets.
If you need a custom version of an existing Widget,
you can make a custom version of that widget.
In Android Studio it is useful to use
the Goto Definition Command-b
(Mac) or Ctrl-B (Windows).

26. Haven’t installed
Flutter yet!

27. Haven’t installed
Flutter yet!
Ensure your path is setup.
Install Xcode 9.+ so you can use it’s simulator
(Mac or Mac VM only)
Install Android Studio 3.2.1 (No Canary channel)

28. More details on
medium.com
https://medium.com/flutterpub/start-building-
your-flutter-tool-belt-f48e88ef6a6e

29. Some of what Flutter
supports:
Material Design
iOS Cupertino Widgets
Gestures
Animation
HTTP and JSON
SQL Database
Shared Preferences
File I/O
Firebase
Firebase Cloud Messaging
(native configs required)
Web View (url launcher)

30. Flutter Resources
flutter.io
dartlang.org
Google IO 2018
Udacity - https://www.udacity.com/course/build-native-mobile-
apps-with-flutter--ud905
GDG Bronx - Flutter Study Jam
New York Flutter Developer Meetup
GDG Meetups
Udemy
On YouTube:
DartConf 2018
FlutterChallenge
Tensor Programming Flutter

31. Questions?

32. Thank You
Linkedin: www.linkedin.com/in/peterjbirdsall
eMail: peter.j.birdsall@gmail.com
Peter Birdsall