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Programming for Android
Boutsis Ioannis
[email protected]
History
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Android is developed by the Open Handset Alliance led by
Google
Google purchased the initial developer of the software,
Android Inc., in 2005
Android's source code is released by Google under open
source licenses
Android Growth
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As of July 2013, the Google Play store had over one million
Android apps published, and over 50 billion downloads
At Google I/O 2014, the company revealed that there were
over one billion active monthly Android users, up from 538
million in June 2013
A 2015 survey found that 40% of full-time professional
developers see Android as their priority target platform
Statistics
Platform Characteristics
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This is a mobile OS with limited resources
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Limited memory, processing power
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Battery life is critical!
This results in specific architectural decisions
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The OS aggressively flushes memory when not in use
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(i.e. it will page apps in and out of memory)
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Background computation is extremely limited
Unusual device characteristics
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Small screen, typically focused on a single app
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Gestural input
Architectural Overview
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Layered environment
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Linux 2.6 kernel
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Core Android libraries/services built on top
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Top‐most layer runs in a VM
Application management
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Applications are built in Java, running in a Dalvik VM
(now ART)
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Each application is a separate user/process/VM!
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Applications can share services and capabilities
Architecture
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Applications
All applications are written using the Java programming language.
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Application Framework
By providing an open development platform, Android offers developers the ability to build extremely rich and
innovative applications. Developers are free to take advantage of the device hardware, access location information,
run background services, set alarms, add notifications to the status bar, and much, much more.
Developers have full access to the same framework APIs used by the core applications.
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Libraries
Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are
exposed to developers through the Android application framework.
Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has
been written so that a device can run multiple VMs efficiently. The Dalvik VM relies on the Linux kernel for
underlying functionality such as threading and low-level memory management.
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Linux Kernel
Android relies on Linux version 2.6 for core system services such as security, memory management, process
management, network stack, and driver model. The kernel also acts as an abstraction layer between the hardware
and the rest of the software stack.
Architecture
Components
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Core building blocks for Android applications
Activities: Single‐screen of an application / different activity
for each UI screen of the application.
Services: Long‐running background application (e.g. playing
music on the background) / can be bind with a specific activity.
Content Providers: Used to manage access on persistent
data that can be shared on different applications (e.g. contacts
phone numbers).
Broadcast Receivers are used to receive a notification and
respond to that (e.g. receiving an SMS)..
Components communicate with messages called Intents,
which are routed through Android runtime and the Kernel.
Activity Lifecycle
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Your application probably consists of one or two main
activities, each containing a set of views (i.e. Java views and
components)
Activity Lifecycle II
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We focus on activities (i.e. typical UI screens)
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Apps can contain multiple activities (one “main”)
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Activities can create other activities (“Back stack”)
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Navigation forward/back triggered by user actions
How to install Android SDK
Required Installations
Java JDK
http://www.oracle.com/us/technologies/java/index.html
Android Studio
or
Eclipse(NetBeans etc..)
http://www.eclipse.org/downloads/
Download Android Studio
http://developer.android.com/sdk/index.html
Installing Started Package
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In Windows – Easy, guide..
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In Linux – Extract to specific folder
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Android SDK will be installed at startup
Setting up your SDK
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Tools → Android → SDK Manager
INSTALL Android Versions
Create new Android Virtual Device
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Tools → Android → AVD Manager
Run Project as Android application
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When executing an android project through Android
Studio we should now be able to choose our
mobile/simulator
Ready to Start!!
Programming...
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Android Manifest
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XML based User Interface
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Java Code
http://developer.android.com/guide/topics/ui/index.html
Android Manifest
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Every application must have an AndroidManifest.xml file (with
precisely that name) in its root directory.
The manifest presents essential information about the
application to the Android system.
Activities, Permissions, Minimum Android Level, etc. should
be declared in the manifest.
More Info:
http://developer.android.com/guide/topics/manifest/manifest-intro.html
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.test.android"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk android:minSdkVersion="8" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name" >
<activity
android:label="@string/app_name"
android:name=".TestAndroidActivity" >
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER"
/>
</intent-filter>
</activity>
<activity android:name=".Activity2"
</activity>
</application>
</manifest>
>
Resources(/res)
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/drawables (low, medium, high)
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/layout (xml Uis)
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/values eg string.xml:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="ds2015">Distributed Systems</string>
<string name="button_enter">Enter</string>
<string name="click_android">Click on the android</string>
<string name="changed_text">Text to be changed</string>
<string name="app_name">TestAndroid</string>
</resources>
Layouts
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/
apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:orientation="vertical" >
<TextView
android:id="@+id/textview"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/ds2015"
android:textSize="20sp"
android:textStyle="bold"
android:gravity="center_vertical|center_horizontal"/>
<ImageView
android:id="@+id/androids"
android:layout_width="234dp"
android:layout_height="246dp"
android:src="@drawable/android1" />
<Button
android:id="@+id/button1"
android:layout_width="150dp"
android:layout_height="wrap_content"
android:gravity="center_vertical|center_horizontal"
android:text="@string/button_enter" />
</LinearLayout>
Layouts
activity2.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/
apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#330000"
android:gravity="center"
android:orientation="vertical" >
<ImageView
android:id="@+id/talking_android"
android:layout_width="180sp"
android:layout_height="80sp"
android:layout_marginBottom="50sp"
android:src="@drawable/android_look" />
<TextView
android:id="@+id/textview"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical|center_horizontal"
android:textSize="16sp"
android:textStyle="italic"
android:text="@string/click_android" />
<TextView
android:id="@+id/textView1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center_vertical|center_horizontal"
android:background="#000066"
android:textColor="#ffcc00"
android:typeface="monospace"
android:text="@string/changed_text" />
</LinearLayout>
Java Code
TestAndroidActivity.java
package com.test.android;
import
import
import
import
import
android.app.Activity;
android.content.Intent;
android.os.Bundle;
android.view.View;
android.widget.Button;
public class TestAndroidActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button next = (Button) findViewById(R.id.button1);
next.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(),
Activity2.class);
startActivityForResult(myIntent, 0);
}
});
}
}
Java Code
Activity2.java
private void androidClick() {
final AlertDialog.Builder alert = new
AlertDialog.Builder(this);
final EditText input = new EditText(this);
alert.setView(input);
alert.setPositiveButton("Change text", new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int
whichButton) {
String value =
input.getText().toString().trim();
changeText(value);
}
});
package com.test.android;
import
import
import
import
import
import
import
import
import
android.app.Activity;
android.app.AlertDialog;
android.content.DialogInterface;
android.os.Bundle;
android.view.View;
android.widget.EditText;
android.widget.ImageView;
android.widget.TextView;
android.widget.Toast;
public class Activity2 extends Activity {
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity2);
alert.setNegativeButton("Cancel",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int
whichButton) {
dialog.cancel();
}
});
final ImageView iv =
(ImageView)findViewById(R.id.talking_android);
alert.show();
// set the listener
iv.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
androidClick();
}
});
}
private void changeText(String value) {
TextView tv = (TextView) findViewById(R.id.textView1);
tv.setText(value);
Toast.makeText(getApplicationContext(), "Text changed!",
Toast.LENGTH_SHORT).show();
}
}
}
Java Code
Διευθυνσιοδότηση
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Στα κινητά οι διευθύνσεις ip δίνονται από το δίκτυο.
Για όσους χρησιμοποιούν τον emulator οι διευθύνσεις ip που χρησιμοποιεί είναι
διαφορετικές από αυτές του υπολογιστή
http://developer.android.com/guide/developing/devices/emulator.html#emulatornet
working
Έτσι, για να συνδεθεί ένας client στο ServerSocket του emulator πρέπει να γίνουν
τα εξής:
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-το serverSocket του emulator ανοίγει στο port που θέλουμε(έστω 5000)
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-Στη συνέχεια πρέπει να κάνουμε redirect κάποιο port σε αυτό.
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Ανοίγουμε ένα telnet στο port που τρέχει ο emulator(πχ 5554) με telnet
localhost 5554
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και εκτελούμε redir add tcp:5001:5000
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-Τώρα κάθε client μπορεί να δημιουργήσει ένα socket για να συνδεθεί
στο αρχικό serverSocket με IP/port: 10.0.2.2:5001
http://developer.android.com/guide/developing/devices/emulator.html#connecting