Getting Started with Sky
Sky apps are written in Dart. To get started, we need to set up Dart SDK:
- Install the Dart SDK:
- Mac:
brew tap dart-lang/dart && brew install dart --devel
- Linux: See https://www.dartlang.org/downloads/linux.html
- Mac:
- Ensure that
$DART_SDK
is set to the path of your Dart SDK and that thedart
andpub
executables are on your$PATH
.
Once you have installed Dart SDK, create a new directory and add a pubspec.yaml:
name: your_app_name
dependencies:
sky: any
sky_tools: any
Next, create a lib
directory (which is where your Dart code will go) and use
the pub
tool to fetch the Sky package and its dependencies:
mkdir lib
pub upgrade
Sky assumes the entry point for your application is a main
function in
lib/main.dart
:
import 'package:sky/widgets.dart';
class HelloWorldApp extends App {
Widget build() {
return new Center(child: new Text('Hello, world!'));
}
}
void main() {
runApp(new HelloWorldApp());
}
Execution starts in main
, which in this example runs a new instance of the HelloWorldApp
.
The HelloWorldApp
builds a Text
widget containing the traditional Hello, world!
string and centers it on the screen using a Center
widget. To learn more about
the widget system, please see the
widgets tutorial.
Setting up your Android device
Currently Sky requires an Android device running the Lollipop (or newer) version of the Android operating system.
-
Install the
adb
tool from the Android SDK: -
Mac:
brew install android-platform-tools
-
Linux:
sudo apt-get install android-tools-adb
- If the version of
adb
provided by your Linux distribution is too old, you might need to install the Android SDK manually.
- If the version of
-
Enable developer mode on your device by visiting
Settings > About phone
and tapping theBuild number
field five times. -
Enable
Android debugging
inSettings > Developer options
. -
Using a USB cable, plug your phone into your computer. If prompted on your device, authorize your computer to access your device.
Running a Sky application
The sky
pub package includes a sky_tool
script to assist in running
Sky applications inside the SkyShell.apk
harness. The sky_tool
script
expects to be run from the root directory of your application's package (i.e.,
the same directory that contains the pubspec.yaml
file).
To run your app with logging, run this command:
./packages/sky/sky_tool start --checked && ./packages/sky/sky_tool logs
The sky_tool start
command starts the dev server and uploads your app to the device, installing SkyShell.apk
if needed.
The --checked
flag triggers checked mode, in which types are checked, asserts are run, and
various debugging features are enabled.
The sky_tool logs
command logs errors and Dart print()
output from the app, automatically limiting the output to just output from Sky Dart code and the Sky Engine C++ code (which
for historical reasons currently uses the tag chromium
.)
To avoid confusion from old log messages, you may wish to call sky_tool logs --clear
before calling
sky_tool start
, to clear the log between runs.
Rapid Iteration
As an alternative to running ./packages/sky/sky_tool start
every time you make a change,
you might prefer to have the SkyShell reload your app automatically for you as you edit. To
do this, run the following command:
./packages/sky/sky_tool listen
This is a long-running command -- just press ctrl-c
when you want to stop listening for
changes to the file system and automatically reloading your app.
Currently sky_tool listen
only works for Android, but iOS device and iOS simulator support
are coming soon.
Debugging
Sky uses Observatory for
debugging and profiling. While running your Sky app using sky_tool
, you can
access Observatory by navigating your web browser to
http://localhost:8181/.
Building a standalone APK
Although it is possible to build a standalone APK containing your application,
doing so right now is difficult. If you're feeling brave, you can see how we
build the Stocks.apk
in
examples/stocks.
Eventually we plan to make this much easier and support platforms other than
Android, but that work still in progress.