golab-2017-training.slide

Write your next Android app in Go
GoLab, Florence 2017

Elias Naur
elias.naur@gmail.com
@elias_naur

: Hi everyone. This training session is about at least some of the nitty-gritty details of using Go in your Android apps.

: Since this is going to be a hands-on session, I'd like to start by getting the boring details done first.

* Prerequisites

- Laptop running a 64 bit OS; Linux, macOS or Windows.
- Go 1.7 (64 bit).
- Android SDK/Android studio.
- Android NDK (64 bit), downloaded through the Android SDK manager. Command line:
   sdkmanager ndk-bundle
- A working and recent Android device or emulator.
- On a device, enable developer mode and USB debugging.

: I'd like you to go through these requirements, and make sure you've got the Android SDK or Android Studio installed in a recent version.

: Then, I'd like you to download the Android NDK for your platform, preferably through the Android SDK manager. You can access the manager inside Android Studio, or you can run the sdkmanager tool with the argument ndk-bundle. I prefer the command line tool because I don't have much experience with Android Studio.

: Let's take a few minutes for everyone to get ready.

: Please do speak up if you're stuck. The rest of this session won't be that interesting if you can't actually run your Go Android apps.

* Setup

- Environment
- ANDROID_HOME should point to your Android SDK
- gomobile
	$ go get -u golang.org/x/mobile/cmd/...
	$ gomobile init

: Now, with everything installed, go get the gomobile and gobind tools through the go command.

: Then, initialize the gomobile environment with the gomobile init command.

* Training files

Slides 

	https://talks.godoc.org/github.com/eliasnaur/golab-2017-training/golab-2017-training-nocomments.slide#13

Example code

    $ git clone https://github.com/eliasnaur/golab-2017-training.git

Add the golab-2017-training directory to your GOPATH.

: To make it easier to start, I've added a very basic Android app you can use as a starting point for your own apps.

: The project, basic, is set up to use the support library, the databinding library and finally, to use gomobile to bind your Go packages.

* The first run

	$ cd golab-2017-basic/basic

Linux/macOS

    $ ./gradlew installDebug

Windows

    $ gradlew.bat installDebug

: If everything went well, you should now have a "Basic" app on your emulator or device.

: Now, let's take 15-20 minutes for you to get everything working and to play around with the project. Try to edit the goapp.go source file, the layout file activity_main.xml or the MainActivity.java file.

* Logging

    $ abd log cat -s Go:* GoLog:*

Java

	android.util.Log.i("Go", ...);


* Structs

Go

    type AGoStruct struct {
      ...
    }

    func NewAGoStruct() *AGoStruct {
      ...
    }

    func (s *AGoStruct) AGoMethod() {
      ...
    }

Java

	goapp.AGoStruct s = new goapp.AGoStruct();
	s.aGoMethod()

: Now that you can call a simple Go function from Java, try to add a Go struct, with a constructor and a method.

: Remember to lower case the first letter of the method when calling it from Java.

: Then, instantiate it from Java and call the method.

: Try to add more methods, taking arguments or returning values.

* Structs (cont.)

You can use all the basic types (string, int, float32 etc.), other structs and interfaces.

Go

	func F(str *GoStruct, interf GoInterface, i int, f float32) string

* Go interfaces

Go

	type SomeGoInterface interface {
		F(i int) string
	}

Java

	class ImplementsGo implements goapp.SomeGoInterface {
		@Override public String f(i long, s goapp.AGoStruct) {
			...
		}
	}

: Let's try adding a Go interface to the goapp package.

* Go interfaces (cont.)

Go

	func TakesAnInterface(i SomeGoInterface) string {
		return i.F(10)
	}

Java

	String res = goapp.takesAnInterface(new ImplementsGo());
	android.util.Log.i("Go", "The result: " + res);

: Then, implement that interface in Java, and use it from Go.

* Reverse bindings

Go

	package gorev

	import (
		"Java/android/os"
		"Java/android/support/v7/app"

		"Java/android/databinding/DataBindingUtil"
		"Java/gorev/databinding/ActivityMainBinding"

		rlayout "Java/gorev/R/layout"

		// The Java package for "gorev".
		gopkg "Java/gorev"
	)

	type GoActivity struct {
		app.AppCompatActivity
	}


* Reverse bindings (cont.)

	func (a *GoActivity) OnCreate(this gopkg.GoActivity, b os.Bundle) {
		this.Super().OnCreate(b)
			db := DataBindingUtil.SetContentView(this, rlayout.Activity_main)
			binding := ActivityMainBinding.Cast(db)
			binding.SetText("Hello from the reverse")
	}