Getting Started with Sky

Sky apps are written in Dart. To get started, we need to set up Dart SDK:

  • Install the Dart SDK.
  • Ensure that $DART_SDK is set to the path of your Dart SDK.

Once we have the Dart SDK, we can creating a new directory and adding a pubspec.yaml:

name: your_app_name
dependencies:
  sky: any

Once the pubspec is in place, create a lib directory (where your dart code will go) ensure that the ‘dart’ and ‘pub’ executables are on your $PATH and run the following:

  • mkdir lib
  • pub get && pub run sky:init

Currently the Sky Engine assumes the entry point for your application is a main function in lib/main.dart:

import 'package:sky/widgets/basic.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 instructs the framework to run a new instance of the HelloWorldApp. The framework then calls the build() function on HelloWorldApp to create a tree of widgets, some of which might be other Components, which in turn have build() functions that generate more widgets iteratively to create the widget hierarchy. To learn more about the widget system, please see the widgets tutorial.

Setup 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 and ensure that adb (inside platform-toolsin the Android SDK) is in your$PATH`.

  • Enable developer mode on your device by visiting Settings > About phone and tapping the Build number field five times.

  • Enable USB debugging in Settings > 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 SkyDemo.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, follow these instructions:

  • ./packages/sky/sky_tool start to start the dev server and upload your app to the device. (NOTE: add a --install flag to install SkyDemo.apk if it is not already installed on the device.)

  • Use adb logcat to view any errors or Dart print() output from the app. adb logcat -s sky can be used to filter only adb messages from SkyDemo.apk.

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 example/stocks. Eventually we plan to make this much easier and support platforms other than Android, but that work still in progress.

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/.