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Create iOS and Android Programming with Go

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Next install the GoMobile tool which compiles and runs pre-existing Go applications for Android and iOS

Introduction

Next install the GoMobile tool which compiles and runs pre-existing Go applications for Android and iOS:

go get golang.org/x/mobile/cmd/gomobile
gomobile init

We will be referring to the example applications shipped with the gomobile package inGoLangInstalldir/src/golang.org/x/mobile/example/. If you don’t have them installed, fetch them with this command :

go get -d golang.org/x/mobile/example/basic

Build and Install a Native Go Application

For many application use cases, compiling Go to a native application and ignoring platform libraries and interfaces may be fine. If so it’s simple to compile your existing Go code, with a subset of functionality available. This includes:

  • App control and configuration
  • OpenGL ES 2 bindings
  • Asset management
  • Event management
  • Experimental packages include OpenAL bindings, audio, font, sprite and motion sensors

We will be using one of the pre-existing gomobile examples to step through the process, but these can be replaced with your own project files.

Android

Build an Android APK

gomobile build -target=android golang.org/x/mobile/example/basic

Deploy to a Device

gomobile install golang.org/x/mobile/example/basic

iOS

Build an iOS IPA

gomobile build -target=ios golang.org/x/mobile/example/basic

Deploy to a device

There is no equivalent command for deployment on iOS as on Android, so after creating the app above you will have to follow your own personal favorite way of copying it to a device or emulator, such as the ios-deploy tool.

For something a bit more exciting, also try the steps above with the golang.org/x/mobile/example/audioexample.

Let’s take a look inside the audio example (I wont reproduce the complete code here) and you don’t need to be overly familiar with GoLang (I’m not), this is more about looking at what is possible.

Firstly you see a set of import statements:

import (
...
    "golang.org/x/mobile/app"
    "golang.org/x/mobile/asset"
...
)

If you dig around the folders and files that are imported in GoLangInstalldir/src/golang.org/x/mobile/* you will notice the various Java and Objective-C files that are compiled with your code.

Digging further you will see references to some of the classes imported and used in the code, such asapp and glctx.

Going Native

We can code in Go and build a compact and optimized native app, but it’s not very ‘native-like’ right now, as all the required support libraries are only available in Java and Objective-C / Swift. How can we improve this experience?

The Go Mobile team have created another option, using go packages (your applications) inside a native application. Perfect for sharing some common Go code and binding to native code. It’s easy to get started, but may be complex to maintain in the long run.

Android

If you’re using Android Studio, import the reference project fromGoLangInstalldir/src/golang.org/x/mobile/example/bind/android and open the build.grade (Module: hello)file to update your GOPATH and GO paths, here are mine (I installed GoLang with Homebrew):

Paths

Sync Gradle and the application is then deployable to an emulator or device.

Let’s look at the Java and Go code:

MainActivity.java

package org.golang.example.bind;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

import go.hello.Hello;

public class MainActivity extends Activity {

    private TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTextView = (TextView) findViewById(R.id.mytextview);

        // Call Go function.
        String greetings = Hello.Greetings("Android and Gopher");
        mTextView.setText(greetings);
    }
}
src/golang.org/x/mobile/example/bind/hello/hello.go

package hello

import "fmt"

func Greetings(name string) string {
    return fmt.Sprintf("Hello, %s!", name)
}

The go file is imported with import go.hello.Hello and the Greetings function within it accessible in the Java file via Hello.Greetings. With not too many extra steps, bindings between go functions and native UI elements are possible.

iOS

Binding an iOS application to Go requires different steps. First execute the following commands:

cd GoLang_Install_dir/src/golang.org/x/mobile/example/bind
gomobile bind -target=ios golang.org/x/mobile/example/bind/hello

This will create a framework bundle called Hello.framework in the current folder that we can use in our project.

Open the sample iOS project found atGoLangInstalldir/src/golang.org/x/mobile/example/bind/ios/bind.xcodeproj in Xcode and dragHello.framework into the project, checking Copy items if needed. This should result in the following folder structure:

Go in Xcode

Build and run the application which, much like the Android app, calls Go methods into Objective-C code.

Let’s look at the code:

#import "ViewController.h"
#import "hello/Hello.h"  // Gomobile bind generated header file in hello.framework

@interface ViewController ()
@end

@implementation ViewController

@synthesize textLabel;

- (void)loadView {
    [super loadView];
    textLabel.text = GoHelloGreetings(@"iOS and Gopher");
}

@end

#import "hello/Hello.h" imports the framework file generated earlier andtextLabel.text = GoHelloGreetings(@"iOS and Gopher"); calls the function it exposes to set a label variable.

It’s possible to use the same auto-generated Objective-C framework file in a Swift based project and then use something like:

let msg = Hello.GoHelloGreetings("gopher")

 

Create iOS and Android Programming with Go

Create iOS and Android Programming with Go Posted on 25-02-2016  Next install the GoMobile tool which compiles and runs pre-existing Go applications for Android and iOS 3/10 501

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