README Android (0.5.1)
LiquidCore enables Node.js virtual machines to run inside Android and iOS apps. It provides a complete runtime environment, including a virtual file system and native MySQL support.
LiquidCore also provides a convenient way for Android developers to execute raw JavaScript inside of their apps, as iOS developers can already do natively with JavaScriptCore.
0.5.1 - Get it through JitPack
This section covers the two major intended use cases of LiquidCore, complete with Hello, World! step-by-step examples.
You can also use LiquidCore as a raw Native Javascript Engine (i.e. as a replacement for AndroidJSCore). That topic is discussed here.
A micro app is built on a micro service. A micro service is nothing more than an independent Node.js instance whose startup code is referenced by a URI. For example:
MicroService service = new MicroService(androidContext,
new URI("http://my.server.com/path/to/code.js"));
service.start();The service URI can either refer to a server URL or a local Android resource. LiquidCore is designed to primarily use remote URLs, as dynamic updates are an important value proposition, but local resources are also supported. For example, android.resource://com.example.myapp/raw/some_js_file, where some_js_file.js resides in res/raw/some_js_file.js (note that the .js is omitted from the URI when using an Android resource).
A micro service can communicate with the host app once the Node.js environment is set up. This can be determined by adding a ServiceStartListener in the MicroService constructor:
MicroService service = new MicroService(
androidContext,
new URI("http://my.server.com/path/to/code.js"),
new MicroService.StartServiceListener() {
@Override
public void onStart(MicroService service) {
// .. The environment is live, but the startup JS code (from the URI)
// has not been executed yet.
}
}
);
service.start();A micro service communicates with the host through a simple EventEmitter interface, eponymously called LiquidCore. For example, in your JavaScript startup code (code.js in this example):
LiquidCore.emit('my_event', {foo: "hello, world", bar: 5, l337 : ['a', 'b'] })On the Java side, the host app can listen for events:
// ... in the StartServiceListener.onStart() method:
service.on("my_event", new MicroService.EventListener() {
@Override
public void onEvent(MicroService service, String event, JSONObject payload) {
try {
android.util.Log.i("Event:" + event, payload.getString("foo"));
// logs: I/Event:my_event: hello, world
} catch (JSONException e) {
e.printStackTrace();
}
}
});Similarly, the micro service can listen for events from the host:
JSONObject payload = new JSONObject();
payload.put("hallo", "die Weld");
service.emit("host_event", payload);Then, in Javascript:
LiquidCore.on('host_event', function(msg) {
console.log('Hallo, ' + msg.hallo)
})LiquidCore creates a convenient virtual file system so that instances of micro services do not unintentionally or maliciously interfere with each other or the rest of the Android filesystem. The file system is described in detail here.
Important Notice: The Micro App concept is being completely re-thought. In version 0.6.0, LiquidView will disappear from LiquidCore and be reborn in a separate project built on top of LiquidCore. The goal is to keep LiquidCore focused on just providing a fast, secure Node VM for mobile devices. The UI will reappear in a project called caraml. Stay tuned.
There are many uses for micro services. They are really useful for taking advantage of all the work that has been done by the Node community. But we want to be able to create our own native applications that do not require much, if any, interaction from the host. To achieve this, we will introduce one more term: Surface. A surface is a UI canvas for micro services.
There are two surfaces so far:
-
ConsoleSurface. AConsoleSurfaceis simply a Node.js terminal console that displays anything written toconsole.log()andconsole.error(). It also allows injection of Javascript commands, just like a standard Node console. Run the NodeConsole app under theTestsdirectory to see it in action. -
ReactNativeSurface. You can drive native UI elements using the React Native framework from within your micro app.
There are other surfaces under consideration, including:
-
WebSurface- aWebViewfront-end where a micro service can write to the DOM -
CardSurface- a limited feature set suitable for driving card-like UI elements in a list -
OpenGLSurface- an OpenGL canvas
Eventually, we would like to have virtual/augmented reality surfaces, as well as non-graphical canvases such as chat and voice query interfaces.
- A recent version of Node.js -- 8.9.3 or newer
- Android Studio
(You can find all the code below in a complete example project here if you get stuck).
To use a micro service, you need two things: the micro service code, and a host app.
We will start by creating a very simple micro service, which does nothing more than send a welcome message to the host. This will be served from a machine on our network. Start by installing the command-line interface:
$ npm install -g liquidcore-cli
Next, generate a project called helloworld using the tool:
$ liquidcore init helloworld
$ cd helloworld && npm install
This will generate a small Hello World project for you. We are going to change it a bit, but the important thing is that this sets everything up correctly and provides you with some nice features like a development server and production bundler.
Once installation has completed, edit the file index.js in your helloworld directory and replace its contents with the following:
/* Hello, World! Micro Service */
// A micro service will exit when it has nothing left to do. So to
// avoid a premature exit, let's set an indefinite timer. When we
// exit() later, the timer will get invalidated.
setInterval(function() {}, 1000)
// Listen for a request from the host for the 'ping' event
LiquidCore.on( 'ping', function() {
// When we get the ping from the host, respond with "Hallo, die Weld!"
// and then exit.
LiquidCore.emit( 'pong', { message: 'Hallo, die Weld!' } )
process.exit(0)
})
// Ok, we are all set up. Let the host know we are ready to talk
LiquidCore.emit( 'ready' )Finally, you can now run your development server.
$ npm start server
This will fire off a server built on the metro bundler. Metro does everything we need and more, so if you've used the old liquidserver in the past, this replaces that. Anyway, congratulations, you just created a micro service. You can test that it is working correctly by navigating to
http://localhost:8082/liquid.bundle?platform=android in your browser. You should be able to find the contents of index.js that you just created with some additional wrapper code. The wrapper is simply
to allow multiple Node.js modules to be packed into a single file. If you were to
require() some other module, that module and its dependencies would get wrapped into this
single file.
You can leave that running or restart it later. Now we need to create a host app.
- In Android Studio, create a new project by selecting
File -> New Project ... - Fill out the basics and press
Next(Application Name:HelloWorld, Company Domain:liquidplayer.org, Package name:org.liquidplayer.examples.helloworld) - Fill in the Target Devices information. The defaults are fine. Click
Next - Select
Empty Activityand thenNext - The default options are ok. Click
Finish
You now have a basic app that does very little. Go ahead and run it in your emulator. If you hadn't figured out why we are creating a "Hallo, die Weld!" app, you probably can see why by now. You already get "Hello, World!" from Android Studio. We're going to make it speak German with our micro service.
Next, open the res/layout/activity_main.xml file. We need to make a couple of modifications. Replace the contents with the following:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="org.liquidplayer.examples.helloworld.MainActivity">
<TextView
android:id="@+id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="Sprechen Sie Deutsch!"
/>
</RelativeLayout>All we've changed is that we have given our TextView a name: text, and added a button. Go ahead and run it again. You should now see a big button in the middle.
Now it is time to connect LiquidCore. First, you must add the library. Go to your root-level build.grade
file and add the jitpack dependency:
...
allprojects {
repositories {
jcenter()
maven { url 'https://jitpack.io' }
}
}
...
Then, add the LiquidCore library to your app's build.gradle:
dependencies {
...
implementation 'com.github.LiquidPlayer:LiquidCore:0.5.1'
}
Go ahead and sync to make sure the library downloads and links properly. Run the app again to ensure that all is good.
Now, let's connect our button to the micro service. Edit MainActivity.java in our app, and replace the contents with the following:
package org.liquidplayer.examples.helloworld;
import android.os.Handler;
import android.os.Looper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import org.json.JSONException;
import org.json.JSONObject;
import org.liquidplayer.service.MicroService;
import org.liquidplayer.service.MicroService.ServiceStartListener;
import org.liquidplayer.service.MicroService.EventListener;
import java.net.URI;
import java.net.URISyntaxException;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView textView = (TextView) findViewById(R.id.text);
final Button button = (Button) findViewById(R.id.button);
// Our 'ready' listener will wait for a ready event from the micro service. Once
// the micro service is ready, we'll ping it by emitting a "ping" event to the
// service.
final EventListener readyListener = new EventListener() {
@Override
public void onEvent(MicroService service, String event, JSONObject payload) {
service.emit("ping");
}
};
// Our micro service will respond to us with a "pong" event. Embedded in that
// event is our message. We'll update the textView with the message from the
// micro service.
final EventListener pongListener = new EventListener() {
@Override
public void onEvent(MicroService service, String event, final JSONObject payload) {
// NOTE: This event is typically called inside of the micro service's thread, not
// the main UI thread. To update the UI, run this on the main thread.
new Handler(Looper.getMainLooper()).post(new Runnable() {
@Override
public void run() {
try {
textView.setText(payload.getString("message"));
} catch (JSONException e) {
e.printStackTrace();
}
}
});
}
};
// Our start listener will set up our event listeners once the micro service Node.js
// environment is set up
final ServiceStartListener startListener = new ServiceStartListener() {
@Override
public void onStart(MicroService service) {
service.addEventListener("ready", readyListener);
service.addEventListener("pong", pongListener);
}
};
// When our button is clicked, we will launch a new instance of our micro service.
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
URI uri = MicroService.DevServer();
MicroService service = new MicroService(MainActivity.this, uri, startListener);
service.start();
} catch (URISyntaxException e) {
e.printStackTrace();
}
}
});
}
}Now, restart the app and then click the button. The "Hello World" message should change to German. You have successfully connected a micro service to a host app!
To demonstrate the instant update feature, leave the app and server running. Now, edit index.js on your server machine to respond with a different message and then save:
...
LiquidCore.emit( 'pong', { message: 'Das ist super!' } )
...Go back to the app and press the button again. Your message should update.
That's it. That's all there is to it. Of course, this is an overly simplified example. You have all of the capabilities of Node.js at your disposal.
A quick note about the MicroService.DevServer(): this generates convenience URL which points to the loopback address (10.0.2.2) on Android, which is used to serve the emulator from the host machine. This won't work on actual hardware. You would need to replace this with an actual URL. MicroService.DevServer() assumes the entry file is named liquid.js and the server is running on port 8082. Both of these assumptions can be changed by providing arguments, e.g. MicroService.DevServer("another_file.bundle", 8888) would generate a URL to fetch a bundle with an entry point of another_file.js on port 8888.
If you are interested in building the library directly and possibly contributing, you must do the following:
% git clone https://github.com/liquidplayer/LiquidCore.git
% cd LiquidCore
% echo ndk.dir=$ANDROID_NDK > local.properties
% echo sdk.dir=$ANDROID_SDK >> local.properties
% ./gradlew assembleRelease
Your library now sits in LiquidCoreAndroid/build/outputs/aar/LiquidCore-release.aar. To use it, simply
add the following to your app's build.gradle:
repositories {
flatDir {
dirs '/path/to/lib'
}
}
dependencies {
implementation(name:'LiquidCore-release', ext:'aar')
}
The Node.js library (libnode.so) is pre-compiled and included in binary form in
deps/node-8.9.3/prebuilt. All of the modifications required to produce the library are included in deps/node-8.9.3. To build each library (if you so choose), see the instructions here.
Copyright (c) 2014-2018 Eric Lange. All rights reserved.
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