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First activities

  1. Applications, processes and threads
    1. Process
    2. Threads
      1. Main thread
      2. Utility threads
      3. Secondary threads
      4. Coroutines
  2. Creation of a new project
    1. With an IDE
    2. With the CLI
  3. Typical structure of a project
  4. A first activity: the traditional Hello World !
    1. Building programmatically the user interface
    2. Building the user interface with a XML layout
  5. AndroidManifest.xml : example
  6. Resource management
  7. Internationalization of HelloWorld
    1. File res/values/strings.xml
    2. File res/values-fr/strings.xml
    3. Using the string reference
    4. String with placeholders
  8. Compilation of the project
    1. Compilation chain
    2. Using Gradle
      1. Gradle configuration files
      2. Build variants
      3. Sets of sources
      4. Example of a build.gradle file for a module
  9. Paquetages d'applications Android
    1. Fichier APK
    2. Fichier AAR
  10. Tester un projet
  11. Logcat
  12. DDMS
  13. Tâches
  14. Comportements spécifiques pour les instances d'activité
  15. Cycle de vie d'une activité
  16. Listeners de changement d'état

Applications, processes and threads

Process

Order of precedence for the importance of an application (process):

  1. Foreground process
    • One of its activities is visible on the top of the screen
    • One of its BroadcastReceiver is currently running (onReceive method)
    • One of its Service has a running event method (onCreate, onStart, onDestroy)
  2. Visible process
    • One of its activities is partially visible
    • One of its Service is running as a foreground service
  3. Service process
    • One of its Service is running (but not as a foreground service)
  4. Cached process
    • A process that is kept in cache in memory

☞ An application that is used by an application with more priority inherits of its priority
Example: if an application A with a visible activity uses the ContentProvider of an application B, B will be considered also as a foreground process

Threads

Main thread

Utility threads

Secondary threads

Coroutines

Case of Thread.sleep and suspend fun delay:

Creation of a new project

With an IDE

With Android Studio (File > New Project wizard):

With the CLI

android create project 
	--target <target_ID> \
	--name <your_project_name> \
	--path path/to/your/project \
	--activity <your_activity_name> \
	--package <your_package_namespace>

From the API level 19, the options -g -v 0.10 (0.10 to be replaced by the Gradle version) allow to create a project managed by Gradle rather than Ant.

One can update a project from a previous SDK:

android update project \
	--name <project_name> \
	--target <target_ID> \
	--path <path_to_your_project>

Typical structure of a project

Project structure Source

A first activity: the traditional Hello World !

Building programmatically the user interface

We can build the user interface with Java code.

// Code sample from Coursand [http://igm.univ-mlv.fr/~chilowi/], under the Apache 2.0 License

package fr.upem.coursand.helloworld;

import java.util.Date;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Gravity;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;

/**
 * An Hello World example programmed in Java.
 * The simple Hello World layout is installed programmatically.
 */
public class HelloWorldJava extends Activity
{
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		// We must never forget to call the super method in every onX() method overridden in the activity
		super.onCreate(savedInstanceState);
		// We create ourselves the layout rather than loading it from a XML description
		LinearLayout layout = new LinearLayout(this); // New layout: container for the graphical elements
		layout.setOrientation(LinearLayout.VERTICAL);
		TextView tv = new TextView(this);
		tv.setText("Hello World at " + new Date()); // The string should be externalized as a resource
		tv.setGravity(Gravity.CENTER);
		LinearLayout.LayoutParams tvParams =
			new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT /*width*/, LayoutParams.WRAP_CONTENT /*height*/, 1/*weight*/);
		layout.addView(tv, tvParams);
		Button b = new Button(this);
		b.setText("Quit the activity");
		// We choose a weight of 1 for the TextView and 0 for the button (only the TextView will be resized)
		LinearLayout.LayoutParams buttonParams =
			new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT, 0);
		layout.addView(b, buttonParams);
		Button b2 = new Button(this);
		b2.setText("Restart activity");
		layout.addView(b2, buttonParams);
		// We add a listener for the click event of the button to finish the activity
		b.setOnClickListener(view -> finish());
		// We add a listener on a button for the activity to start a new instance of itself
		b2.setOnClickListener(view -> startActivity(new Intent(this, HelloWorldJava.class)));
		setContentView(layout);
	}
}

Building the user interface with a XML layout

Using a XML file to describe the layout is prefered:

<?xml version="1.0" encoding="utf-8"?>
<!-- Code sample from Coursand [http://igm.univ-mlv.fr/~chilowi/], under the Apache 2.0 License -->

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="fr.upem.coursand.helloworld.HelloWorldXml">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />


    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="quitActivity"
        android:text="@string/quit_the_activity" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startNewActivityInstance"
        android:text="@string/restart_the_activity" />


</LinearLayout>

AndroidManifest.xml : example

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="fr.upemlv.helloworld"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="16" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppBaseTheme" >
        <activity
            android:name="fr.upemlv.helloworld.HelloWorld"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Some notes:

Resource management

Internationalization of HelloWorld

Android Studio proposes an embedded editor to internationalize the strings. One can also edit the XML files by hand.

File res/values/strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello_world">Hello World UMLV!</string>
</resources>

File res/values-fr/strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello_world">Bonjour le monde UMLV !</string>
</resources>

Using the string reference

tv.setText(R.string.hello_world);

String with placeholders

One can put printf-like pladeholders in the strings that can be replaced:

<string name="hello_world">Hello World to %s, you are %d year old!</string>


tv.setText(getString(R.string.hello_world, "foobar", 42));

Compilation of the project

Compilation chain

Some explanations to compile a project from command-line can be found in this tutorial

Using Gradle

Gradle configuration files

Build variants

Sets of sources

Example of a build.gradle file for a module

apply plugin: 'com.android.application'

android {
	compileSdkVersion 28
	buildToolsVersion "29.0.0"

	defaultConfig {
		applicationId 'com.example.myapp'
		minSdkVersion 15
		targetSdkVersion 28
		versionCode 1
		versionName "1.0"
	}
	
	buildTypes {
		release {
			minifyEnabled true // Enables code shrinking for the release build type.
			proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
		}
	}

  
  flavorDimensions "cost", "google"
  productFlavors {
    free {
      dimension "cost"
      applicationId 'com.example.myapp.free'
    }

    paid {
      dimension "cost"
      applicationId 'com.example.myapp.paid'
    }
    
    premium {
      dimension "premium"
      applicationId 'com.example.myapp.premium'
      // we can add a new source set in /app/src/premium for the additional features
    }
    
    withGoogleApi {
      dimension "google"
      
      dependencies {
		implementation 'com.google.android.gms:play-services-gcm:17.0.0'
		implementation 'com.google.android.gms:play-services-location:17.0.0'
	  }
	}
	
	withoutGoogleApi {
	  dimension "google"
	}
  }
}

dependencies {
    implementation project(":lib")
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation fileTree(dir: 'libs', include: ['*.jar'])
}

Paquetages d'applications Android

Fichier APK

Fichier AAR

Tester un projet

Logcat

DDMS

Tâches

Comportements spécifiques pour les instances d'activité

Ajout d'un intent-filter pour permettre le lancement depuis le launcher :

<activity ... >
    <intent-filter ... >
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
    ...
</activity>

Cycle de vie d'une activité

Diagramme de cycle de vie

Listeners de changement d'état

Etat des activités en premier-plan en mode multi-fenêtré :

Exemple : activité qui loggue tous les événements du cycle de vie avec logcat et les affiche dans un TextView

// Code sample from Coursand [http://igm.univ-mlv.fr/~chilowi/], under the Apache 2.0 License

package fr.upem.coursand.lifecycle;

import android.os.SystemClock;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import fr.upem.coursand.R;

public class LifeCycleActivity extends AppCompatActivity {

    private TextView logView;
    private long startTimestamp;

    protected void log(String message) {
        Log.i("lifeCycleEvent", message);
        logView.append((SystemClock.elapsedRealtime() - startTimestamp) + " ms, " + message + "\n");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        startTimestamp = SystemClock.elapsedRealtime(); // in millis
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_life_cycle);
        logView = findViewById(R.id.logView);
        log("onCreate");
    }

    @Override
    protected void onStart() {
        super.onStart();
        log("onStart");
    }

    @Override
    protected void onStop() {
        super.onStop();
        log("onStop");
    }

    @Override
    protected void onPause() {
        super.onPause();
        log("onPause");
    }

    @Override
    protected void onResume() {
        super.onResume();
        log("onResume");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        log("onRestart");
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        log("onDestroy"); // will not see in the TextView
    }
}