Lalu masuk ke app > manifests > AndroidManifest.xml . Tambahkan perizinan untuk koneksi ke internet<uses-permission android:name=”android.permission.INTERNET” />
Sekarang kita coba running dengan emulator . Klik tombol hijau yang ada di menu bar
Pilih emulator yang ingin anda gunakan, lalu klik OK.
Kemudian pilih app -> java -> id.co.contactperson.contactperson lalu klik kanan seperti gambar dibawah
Isikan nama Package Name services Kemudian klik OK.
Sekarang kita akan buat file .java di dalam package services. Klik kanan pada package services seperti gambar dibawah ini.
Pada isian kolom Name : kita isi dengan ApiClient . Lalu klik OK.
Isikan file java dengan Source Code dibawah ini. Class ini digunakan untuk memulai koneksi dengan APIContactPerson. Untuk Ip dan Nama Folder Server sesuaikan dengan koneksi anda.
Kemudian buatlah sebuah package seperti cara no 9 dengan nama responses.
Kemudian buatlah sebuah file .java seperti cara no 11. Pada kolom isian Name : isi dengan ApiEndPoint lalu kolom Kind : pilih Interface. Lalu klik OK.
Jika berhasil, tampak seperti gambar dibawah.
Sebelum kita membuat fungsi Interface ApiEndPoint, kita buat file di package responses untuk meresponse data dari server. Balik lagi ke phpMyAdmin pilih databse contact_person -> person lalu pilih menu bar Insert. Isi data seeperti gambar dibawah, kemudian klik Go
Buka file php pada folder ContactPerson kemudian ubah sementara source code nya seperti gambar di bawah. Save file yang sudah diubah.
Untuk mendapatkan tampilan data JSON seperti gambar di atas, anda perlu install JSON VIEWER pada web browser anda. Kemudian tekan Crtrl + U pada URL di atas.
Copy isi source data dalam satu baris dari view-source.
Masuk ke link ini http://jsonschema2pojo.org kemudian paste di kotak yang ada. Isi kolom Package sesuai package pada file ApiEndPoint.java lalu isi Class name dengan ReadResponse .
Lalu klik Zip
Lalu klik tulisan warna biru ( ReadResponse-sources.zip ) untuk mendownload
Extract file nya, sampai ada folder baru dengan nama id
Masuk ke dalam folder id sampai ketemu 2 file berikut
Copy 2 file diatas, lalu paste di dalam folder responses pada Android Studio
Lalu buat file StatusResponse.java di dalam folder responses. Kemudian isi kan code berikut
Ok sekarang anda buka file read.php, kemudian kita ubah lagi code nya ke bentuk awal. Jangan lupa untuk save file nya.
Balik lagi keApiEndPoint.javajava , isi kan code di bawah ini.
Aktifkan xampp anda terlebih dahulu. Tekan pada keyboard anda, lalu ketik xampp .
Klik Start pada Apache serta MySQL
Kemudian buka salah satu Web Browser Anda Google Chrome, Mozilla, dll. Lalu ketik http://localhost/dashboard/ pada link URL anda.
Jika sudah muncul tampilan seperti gambar di atas, klik phpMyAdmin.
Klik New.
Isikan nama tabel dengan contact_person . Lalu klik Create.
Isikan kolom Name : dengan person serta Number of columns: 3 . Kemudian klik Go.
Isikan struktur tabel seperti gambar dibawah. Kemudian klik Save.
Jika berhasil, maka muncul tampilan seperti ini.
Sekarang, kita membuat folder untuk Masuk ke folder htdocs anda. Secara default ada di C:\xampp\htdocs . Kemudian buat folder baru dengan nama ContactPerson.
Buka SublimeText anda, lalu masuk ke folder Klik File -> Open Folder … . Pilih Lokasi C:\xampp\htdocs , lalu klik Select Folder.
Sekarang buat file namakan dengan index.php yang berguna untuk menampilkan Tulisan Contact Person API v.1.0 pada halaman index. Isikan file tersebut dengan soruce code di bawah ini .
<?php class ContactPersonApi { public function index() { echo "Contact Person API v.1.0"; } } $contactPersonApi=new ContactPersonApi(); $contactPersonApi->index();
Sekarang buat file namakan dengan models.php yang berguna untuk melakukan koneksi ke databse, serta CRUD query. Isikan file tersebut dengan soruce code di bawah ini .
<?php class database{ //Fungsi constructor untuk membuat koneksi ke database public function __construct(){ $this->db=new PDO('mysql:host=localhost;dbname=contact_person','root','');
}
//Fungsi query untuk mendapatkan data dari database
public function getPersons(){
$query="SELECT * FROM person ";
$sql=$this->db->query($query);
return $sql;
}
public function getPerson($Id){
$query="SELECT * FROM person where id=$Id LIMIT 1";
$sql=$this->db->query($query);
return $sql;
}
public function setPerson($Name,$ContactNumber){
$query="INSERT into person VALUES(null,'$Name','$ContactNumber')";
$sql=$this->db->query($query);
return $sql;
}
public function updatePerson($Id,$Name,$ContactNumber){
$query="UPDATE person SET person_name='$Name',contact_number='$ContactNumber' where id=$Id";
$sql=$this->db->query($query);
return $sql;
}
public function deletePerson($Id){
$query="DELETE FROM person where id=$Id ";
$sql=$this->db->query($query);
return $sql;
}
}
Sekarang buat file namakan dengan create.php yang berguna untuk menyimpan data ke database. Isikan file tersebut dengan soruce code di bawah ini .
<?php include 'models.php'; //Mengambil Data Dari Android $name=$_REQUEST['name']; $contactNumber=$_REQUEST['contact_number']; //Membuat objek dari class database $MakeConnection=new database(); $MakeConnection->setPerson($name,$contactNumber);
//mengirim data ke android dengan format JSON
echo json_encode(array('status'=>true));
?>
Sekarang buat file namakan dengan update.php yang berguna untuk merubah isi data ke database. Isikan file tersebut dengan soruce code di bawah ini .
<?php include 'models.php'; //Mengambil Data Dari Android $id=$_REQUEST['id']; $name=$_REQUEST['name']; $contactNumber=$_REQUEST['contact_number']; //Membuat objek dari class database $MakeConnection=new database(); $MakeConnection->updatePerson($id,$name,$contactNumber);
//mengirim data ke android dengan format JSON
echo json_encode(array('status'=>true));
?>
Sekarang buat file namakan dengan delete.php yang berguna untuk menghapus isi data dari database. Isikan file tersebut dengan soruce code di bawah ini .
<?php include 'models.php'; //Mengambil Data Dari Android $id=$_REQUEST['id']; //Membuat objek dari class database $MakeConnection=new database(); $MakeConnection->deletePerson($id);
//mengirim data ke android dengan format JSON
echo json_encode(array('status'=>true));
?>
Sekarang buat file namakan dengan read.php yang berguna untuk mendapatkan semua data person dari database. Isikan file tersebut dengan soruce code di bawah ini .
<?php include 'models.php'; //Mengambil Data Dari Android $key=$_REQUEST['key']; if (empty($key)) { echo " UnAuthorization User"; }else{ $MakeConnection=new database(); //membuat variable array $jsonResponse=array(); $getObject=$MakeConnection->getPersons();
while ($row=$getObject->fetch(PDO::FETCH_OBJ)) {
$jsonResponse[]=$row;
}
//mengirim data ke android dengan format JSON
echo json_encode(array('status'=>true,'persons'=>$jsonResponse));
}
?>
18. Sekarang buat file namakan dengan readPerson.php yang berguna untuk mendapatkan semua data person dari database. Isikan file tersebut dengan soruce code di bawah ini .
<php
include 'models.php';
//Mengambil Data Dari Android
$key=$_REQUEST['key'];
if (empty($key)) {
echo " UnAuthorization User";
}else{
$MakeConnection=new database();
//membuat variable array
$jsonResponse=array();
$id=$_REQUEST['id'];
$getObject=$MakeConnection->getPerson($id);
while ($row=$getObject->fetch(PDO::FETCH_OBJ)) {
$jsonResponse[]=$row;
}
//mengirim data ke android dengan format JSON
echo json_encode(array('status'=>true,'persons'=>$jsonResponse));
}
?>
Menyambut Ramadhan 1438H, Rumah Coding memberi kesempatan kepada pemiliki blog yang bersifat non komersil untuk memiliki versi android dari blog tersebut secara gratis.
Jika Anda adalah admin dan pengurusan sebuah blog non komersil, anda dapat mengajukan pembuatan aplikasi Android untuk blog anda tersebut. Dengan ketentuan:
Pembuatan aplikasi android hanya berlaku untuk blog non komersil.
Pembuatan aplikasi android tidak bersifat custom. Hanya mengikuti format aplikasi yang kami tawarkan.
Tidak ada iklan apapun dalam aplikasi.
Gratis upload ke Google Play Store menggunakan akun Rumah Coding.
Hanya untuk 60 blog yang terpilih.
Hanya admin dan pengurus blog terkait yang dapat mengajukan pembuatan aplikasi android. Anda tidak diperkenan mengajukan blog yang bukan milik anda. Pada form pengajuan anda akan diminta menyertakan screenshot dashboard dari blog anda untuk otentikasi.
Tampilan aplikasi android untuk blog kurang lebih akan seperti ini:
Tahapan pembuatan aplikasi android:
Mengisi form di bawah paling lambat tanggal 24 Juni 2017.
Blog yang terpilih akan dihubungi secara bertahap melalui whatsapp atau email pada tanggal 1-7 Juli 2017.
Peserta yang terpilih akan diminta melengkapi berbagai macam data untuk keperluan upload ke Google Play Store, seperti icon, deskripsi dan lain-lain.
Proses pembuatan dan upload ke Google Play Store secara bertahap pada tanggal 8-15 Juli 2017
Pada tutorial ini, anda akan belajar membuat sebuah aplikasi android sederhana yang menggunakan List View. Data yang akan ditampilkan adalah kumpulan aplikasi android yang populer di Play Store lengkap dengan icon, total download dan data rating dari masing-masing aplikasi. Data total download dan rating yang kita gunakan dalam tutorial ini bukan merupakan data asli, akan tetapi hanya berupa data dumi untuk tujuan demo.
Data dumi tersebut akan disimpan dalam database MySQL. Kemudian anda juga akan membuat script PHP yang akan mengambil data dumi tadi dari database MySQL. Aplikasi android yang anda buat kemudian memanggil script PHP tadi untuk mengambil data dumi dalam format JSON (Javascript Object Notation). Sebelum saya menjelaskan tahap-tahap pembuatan aplikasi tersebut. Saya akan menjelaskan terlebih dahulu konsep-konsep dasar yang perlu anda pahami.
Mengenal JSON
JSON (Javascript Object Notation) merupakan format pertukaran data. Sebuah objek JSON merupakan kumpulan dari pasangan key dan value yang diawali dengan tanda “{” dan diakhiri dengan tanda “}”. Berikut ini adalah contoh sebuah objek JSON yang akan anda gunakan dalam tutorial ini.
As I’ve stated before, we’ll create simple android application that show a list of top application. We use android list view to display the data. The list data come from MySQL server. So this application will have a http connection feature. Communication between server and android application is use JSON based data. In this tutorial we’ll use apached server in localhost that running AVD (Android Virtual Device).
The data that are fetched from server including applicatoin title, rating, total download and icon name. For simplicity of the tutorial, we’ll use an icons that are saved in /res/drawable folder for applications. This will reduce the complexity of downloading the icons from server.
Below is final screenshot of our tutorial
Populate Listview Using JSON
Server Side Task
1. Creating A Database in MySQL
Before creating a database in MySQL, make sure you’ve create a user to login into the MySQL server. In this tutorial, we use a default user root with blank password.
We’ll create a simple database scheme for the application. The database will be used to store application data. Execute the following sql to create such database.
CREATE DATABASE apps;
Now, we have a database apps. We need to create a table in database apps that will store the application title, total download, rating and icon file name. Execute the following sql to create the table.
CREATE TABLE `app_data`(
`id` int unsigned NOT NULL AUTO_INCREMENT,
`app_title` varchar(150) NOT NULL,
`total_dl` int unsigned NOT NULL default 0,
`rating` int unsigned NOT NULL default 0,
`icon` varchar(120) NOT NULL,
primary key(`id`)
);
Now, we must put sample application data into the table. Execute the following sql to create sample application data.
INSERT INTO app_data VALUES(null, "Facebook", 20099099, 5, "facebook");
INSERT INTO app_data VALUES(null, "Twitter", 11342099, 5, "twitter");
INSERT INTO app_data VALUES(null, "Google +", 10123023, 4, "google");
INSERT INTO app_data VALUES(null, "Whatsapp", 10033876, 3, "whatsapp");
INSERT INTO app_data VALUES(null, "Youtube", 10023444, 4, "youtube");
INSERT INTO app_data VALUES(null, "Line", 9023434, 5, "line");
INSERT INTO app_data VALUES(null, "Kakao Talk", 8247836, 3, "kakao");
INSERT INTO app_data VALUES(null, "Linked In", 784736, 4, "linkedin");
INSERT INTO app_data VALUES(null, "Angry Bird", 693847, 2, "angrybird");
INSERT INTO app_data VALUES(null, "Skype", 528374, 3, "skype");
2. Create PHP Script to Fetch the Data
The database now ready, we need create a PHP script that connect to MySQL server and get the application data. Then the application data is converted into JSON string that will send into client (android application). This script use user root with blank password to login into MySQL server, you can change them to meet your server account.
<?php
$host = "localhost"; // host of MySQL server
$user = "root"; // MySQL user
$pwd = ""; // MySQL user's password
$db = "apps"; // database name
// Create connection
$con = mysqli_connect($host, $user, $pwd, $db);
// Check connection
if(mysqli_connect_errno($con)) {
die("Failed to connect to MySQL: " . mysqli_connect_error());
}
// query the application data
$sql = "SELECT * FROM app_data ORDER By id";
$result = mysqli_query($con, $sql);
// an array to save the application data
$rows = array();
// iterate to query result and add every rows into array
while($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
$rows[] = $row;
}
// close the database connection
mysqli_close($con);
// echo the application data in json format
echo json_encode($rows);
Save above source as PHP file and give a name apps.php and you must place it in apache document root, for example http://localhost/test/apps.php.
3. Testing PHP Script in A Browser
We must test the PHP script we’ve created to make sure the script works well. Open your browser and goto http://localhost/test/apps.php (the url may depend on your environtment). If the script works well, you’ll see the following result in your browser.
JSON In Browser
Client Side Task (Android Application)
After the server side is ready and tested, now we’ll create an android application that will create a http request to PHP script that we’ve created previously to get all application data and display the data in a list view. In order to display all of data like application title, total downloads, rating and icon, we must create a custom adapter for the list view.
Open your Eclipse IDE and create new android application. Use JsonDemo as the project’s name.
Do the following step by step to create the application.
1. Create Main Layout File
This file is an xml layout file that defines the main user interface. It contains a list view that will display all of the application data.
Save below source code as /res/layout/activity_main.xml.
This file is an xml layout file. It responsibles to define a custom view the list view that is contained in the main layout. This file will be used in the custom adapter that will be defined later. The layout contains 3 TextView and 1 ImageView. The image view is used to display the application icon. It is placed on the left. First text view is used to display application’s title. It is placed on the right of the icon. Second text is used to display application’s rating. It is placed on the bottom application’s title. The last text view is used to display the application’ total download.
Save below source code as /res/layout/app_custom_list.xml.
This file is a java object class that represents an application value object. It has several properties that are mapped from the app_data table from our database. It has properties such as application name, total downloads, rating and icon. Below is definition of the file. Below is the source code that define application value object. Save it as /src/com/sj/jsondemo/Application.java.
package com.sj.jsondemo;
public class Application {
private String title;
private long totalDl;
private int rating;
private String icon;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public long getTotalDl() {
return totalDl;
}
public void setTotalDl(long totalDl) {
this.totalDl = totalDl;
}
public int getRating() {
return rating;
}
public void setRating(int rating) {
this.rating = rating;
}
public String getIcon() {
return icon;
}
public void setIcon(String icon) {
this.icon = icon;
}
}
4. Create Custom Adapter File
This file is list view’s custom adapter that will inflate /res/layout/app_custom_list.xml layout file. It’s constructor is defined with 1 parameter. The parameter is an array list of application value object. The adapter will inflates the layout for each application object in the array list and change the application title, rating, total downloads and icons dynamically.
Below is source code that defines the custom adapter. Save it as /src/com/sj/jsondemo/ApplicationAdapter.java.
5. Create An Async Task File To Get The Data From Server
This file responsibles to get all the application data by creating a http request to PHP script. It is defined by subclassed AsyncTask object class. This means the task will be execute in the background, so it never block the user interface. When the task is executed, a progress bar will be shown to make the interface user friendly. This file communicate to activity via a listener that we’ll create later. This communication is important because we need to notify the activity when all the data has been fetched.
Below is the source code that define the async task. Save it as /src/com/sj/jsondemo/FetchDataTask.java.
package com.sj.jsondemo;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.os.AsyncTask;
public class FetchDataTask extends AsyncTask<String, Void, String>{
private final FetchDataListener listener;
private String msg;
public FetchDataTask(FetchDataListener listener) {
this.listener = listener;
}
@Override
protected String doInBackground(String... params) {
if(params == null) return null;
// get url from params
String url = params[0];
try {
// create http connection
HttpClient client = new DefaultHttpClient();
HttpGet httpget = new HttpGet(url);
// connect
HttpResponse response = client.execute(httpget);
// get response
HttpEntity entity = response.getEntity();
if(entity == null) {
msg = "No response from server";
return null;
}
// get response content and convert it to json string
InputStream is = entity.getContent();
return streamToString(is);
}
catch(IOException e){
msg = "No Network Connection";
}
return null;
}
@Override
protected void onPostExecute(String sJson) {
if(sJson == null) {
if(listener != null) listener.onFetchFailure(msg);
return;
}
try {
// convert json string to json array
JSONArray aJson = new JSONArray(sJson);
// create apps list
List<Application> apps = new ArrayList<Application>();
for(int i=0; i<aJson.length(); i++) {
JSONObject json = aJson.getJSONObject(i);
Application app = new Application();
app.setTitle(json.getString("app_title"));
app.setTotalDl(Long.parseLong(json.getString("total_dl")));
app.setRating(Integer.parseInt(json.getString("rating")));
app.setIcon(json.getString("icon"));
// add the app to apps list
apps.add(app);
}
//notify the activity that fetch data has been complete
if(listener != null) listener.onFetchComplete(apps);
} catch (JSONException e) {
msg = "Invalid response";
if(listener != null) listener.onFetchFailure(msg);
return;
}
}
/**
* This function will convert response stream into json string
* @param is respons string
* @return json string
* @throws IOException
*/
public String streamToString(final InputStream is) throws IOException{
BufferedReader reader = new BufferedReader(new InputStreamReader(is));
StringBuilder sb = new StringBuilder();
String line = null;
try {
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
}
catch (IOException e) {
throw e;
}
finally {
try {
is.close();
}
catch (IOException e) {
throw e;
}
}
return sb.toString();
}
}
6. Create Fetch Data Listener
This file is simple Java interface. It has two method’s declarations, onFetchCompleted and onFetchFailure. onFetchCompleted method will be called from FetchDataTask when data fetching is complete. onFetchFailure will be called from FetchDataTask when data fetching is failure.
Save below source code as /src/com/sj/jsondemo/FetchDataListener.java.
package com.sj.jsondemo;
import java.util.List;
public interface FetchDataListener {
public void onFetchComplete(List<Application> data);
public void onFetchFailure(String msg);
}
7. Create Activity
This is main activity that will inflate /res/layout/activity_main.xml to create main user interface. When the activity is created, it’s create new FetchDataTask instance and call execute method of the instance. The task runs and start to get all application data in the background. Before execute the task, the activity show progress bar to the user to indicate that the system is loading the data.
This activity also implements FecthDataListener and overriden onFetchCompleted and onFetchFailure. onFetchFailure is used by activity to hide the progress bar and display failure message to user. onFetchCompleted is used by activity to hide the progress bar and display the application data into the list.
The apache server that we used is localhost which same as host that run AVD(Android Virtual Device), so to refers this host from AVD, we must use IP address 10.0.2.2. For more information please visit Android Developer Site.
Save below source code as /src/com/sj/jsondemo/MainActivity.java.
package com.sj.jsondemo;
import java.util.List;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.widget.Toast;
public class MainActivity extends ListActivity implements FetchDataListener{
private ProgressDialog dialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
}
private void initView() {
// show progress dialog
dialog = ProgressDialog.show(this, "", "Loading...");
String url = "http://10.0.2.2/test/apps.php";
FetchDataTask task = new FetchDataTask(this);
task.execute(url);
}
@Override
public void onFetchComplete(List<Application> data) {
// dismiss the progress dialog
if(dialog != null) dialog.dismiss();
// create new adapter
ApplicationAdapter adapter = new ApplicationAdapter(this, data);
// set the adapter to list
setListAdapter(adapter);
}
@Override
public void onFetchFailure(String msg) {
// dismiss the progress dialog
if(dialog != null) dialog.dismiss();
// show failure message
Toast.makeText(this, msg, Toast.LENGTH_LONG).show();
}
}
8. Create Manifest File
The application make a http request, so the the manifest file must contains network usage permission. Below is complete manifest file. Save it as Android.Manifest.
CSS is an acronym for Cascading Style Sheets, it is used to format web page look. The latest version of CSS is CSS3. This new version of CSS gives web developers more flexibility when styling the webpage. It comes with a set of new rules that make CSS3 better than the old version. CSS3 provides way to create an animation. In this tutorial, we’ll build simple image slider using pure CSS3.
CSS Overview
Before we start into deep explanation to create the slider, I’ll give some overview of CSS feature that is used to create the slider.
Transform Property
The transform property applies a 2D or 3D transformation to an element. This property allows you to rotate, scale, move, skew, etc., elements.
:target Selector
URLs with an # followed by an anchor name, link to a certain element within a document. The element being linked to is the target element. The :target selector can be used to style the current active target element.
:before and :after Selector
The :before selector inserts content before the selected element(s). The :after selector inserts content after the selected element(s).
~ (Tilde Selector)
Tilde selector also called general sibling combination. The general sibling combinator selector is very similar to the adjacent sibling combinator selector. The difference is that that the element being selected doesn’t need immediately succeed the first element, but can appear anywhere after it.
Vendor Specific Property
In order to make our slider runs cross browser, we must add vendor specific property by adding the following prefix into several CSS properties:
-moz-: Mozila Firefox
-webkit-: Safari, Chrome (and other WebKit-based browsers)
-ms-: Microsoft
-o-: Opera
Prepare the Stage
The stage of the slider is a div HTML tag where the slider takes place. We’ll create the stage which have 640px x 320px dimensions. The following HTML tags define the slider stage. We give id [cci]slider[/cci] to the stage.
After the stage has been created, now it’s time to give a style to the stage. At this step, we give dimension, margin, background and shadow to the stage.
We’ll add a drop shadow effect to the stage at the bottom left and bottom right. The drop shadow that we used is simply a blank div element with the following style.
Control buttons is a set of buttons to control the slider. The button is used as a transition trigger for the slider. If user click a button, the slider will change the image on the stage.
Images is the heart of our slider. You can download the images we used in this tutorial by downloading source code. The donwload button is located on the top.
Make The Control Buttons Selected When The Button Clicked
#one:target ~ ul li a[href="#one"],
#two:target ~ ul li a[href="#two"],
#three:target ~ ul li a[href="#three"],
#four:target ~ ul li a[href="#four"],
#five:target ~ ul li a[href="#five"] {
background: #777;
}
#two:target ~ ul li a[href="#one"],
#three:target ~ ul li a[href="#one"],
#four:target ~ ul li a[href="#one"],
#one:target ~ ul li a[href="#one"] {
background: #aaa;
}
Async Task is an android helper class that will allows you to run a background processes. If you are a Java programmer, may be you are familiar with thread. If you run a long task in the main thread, the current user interface will be blocked untill the task has finished. This is not a good practice. To avoid the user interface is being blocked, the long task must be perform in another thread.
Async Task Overview
In android, the only thread that can modify the user interface is called UI thread. This is means you can’t modify user interface from another thread. This is a problem, because in another side, we need to run a long task in separate thread and also we need to update the user interface to display the task progress. Actually, android provides a [cci]Handler[/cci] class that allows you to update the user interface from another thread. But we’ll discuss it in the next tutorial.
Rather than create new thread and handler, android has provides a helper class, [cci]AsyncTask[/cci], to do the same thing. The concept is same, [cci]AsyncTask[/cci] is a smart helper that encapsulates the creation of thread and handler.
[cci]AsyncTask[/cci] must be subclassed to be used. There are three methods that need to be overridden, [cci]doInbackground[/cci], [cci]onProgressUpdate[/cci] and [cci]onPostExecute[/cci]. The first method is mandatory to be overriden, the rest are optional.
[cci]doInbackground[/cci] is a method where the execution codes is placed. [cci]doProgressUpdate[/cci] and [cci]onPostExecute[/cci] run in UI thread, so user interface can be modified in both of methods. Put any codes for displaying the task progress on [cci]doProgressUpdate[/cci]. The [cci]doPostExecute[/cci] method will be called once the task has finished.
[cci]AsyncTask[/cci] is a generic class. [cci]AsyncTask[/cci] is subclassed in the form [cci]AsyncTask<Params, Progress, Result>[/cci].
[cci]Params[/cci], the type of the parameters sent to the task upon execution.
[cci]Progress[/cci], the type of the progress units published during the background computation.
[cci]Result[/cci], the type of the result of the background computation.
To give a better understanding, a sample application that use [cci]AsyncTask[/cci] will be given.
Creating Sample Application
We’ll create a sample application to demonstrate the use of [cci]AsyncTask[/cci] class to perform background processes. Our goal is to create a simple application which download a file from server and display the download progress in the progress bar.
Our application have very simple user interface that only contains a progress bar and a button.
AsyncTask Simple Application
If user click Start Button above, the application will start download a file from server and display the progress in progress bar. After the download process has completed, the file is saved into android root folder (/sdcard).
In this demonstration, I will use a file located on my server, http://semurjengkol.com/dl/files/CustomArrayAdapter.rar(445KB), this is an eclipse project from previous tutorial. You can also use this file or change the url as you want.
Now, open your Eclipse IDE and create new Android Application Project, then follow step by step below:
Create new layout file [cci]res/layout/activity_main.xml[/cci]
This file defines the application main layout which contain a progress bar and a button.
Create new java class [cci]src/DownloadListener.java[/cci]
This is a listener that will be used by [cci]AsyncTask[/cci] to communicate with activity to change the user interface.
package com.sj.asynctask;
import java.io.File;
public interface DownloadListener {
public void onDownloadComplete(File filename);
public void onProgressUpdate(int progress);
public void onDownloadFailure(final String msg);
}
Create new java class [cci]src/DownloadTask.java[/cci]
This file extends [cci]AsyncTask[/cci] and will do the download task and call the listener to display the progress result. The [cci]doInBackground[/cci] method retrieves two string parameters:
URL of the file to be downloaded
The destination storage location to save the file
package com.sj.asynctask;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import android.os.AsyncTask;
import android.os.Environment;
public class DownloadTask extends AsyncTask<String, Integer, Boolean> {
/** This is our listener*/
private final DownloadListener listener;
/** Hold message if download failure*/
private String msg;
/** Save Destination */
private File saveTo;
public DownloadTask(DownloadListener listener) {
this.listener = listener;
}
@Override
protected Boolean doInBackground(String... params) {
/** Params should be array of string with length 2.
* 1. url
* 2. filename destination*/
if(params == null || params.length < 2) {
msg = "Incomplete parameters";
return false;
}
String sUrl = params[0];
String filename = params[1];
/** get root directory: /sdcard */
File rootDir = Environment.getExternalStorageDirectory();
/** create destination file*/
saveTo = new File(rootDir, filename);
try {
/** define url*/
URL url = new URL(sUrl);
/** open the connection*/
URLConnection conn = url.openConnection();
conn.connect();
/** get the size of file that will be downloaded. It will be used to measure the progress*/
int fileLength = conn.getContentLength();
/** create input and outpout stream*/
InputStream is = new BufferedInputStream(url.openStream());
OutputStream os = new FileOutputStream(saveTo);
/** create buffer*/
byte buffer[] = new byte[512];
/** hold total of downloaded bytes*/
long totalDownloaded = 0;
int count;
while ((count = is.read(buffer)) != -1) {
totalDownloaded += count;
/**cause call to onProgressUpdate, which is run on UI thread*/
publishProgress((int) (totalDownloaded * 100 / fileLength));
os.write(buffer, 0, count);
}
/** closing stream*/
os.flush();
os.close();
is.close();
return true;
}
catch (MalformedURLException e) {
msg = "Invalid URL";
}
catch (IOException e) {
msg = "No internet connection";
}
return false;
}
@Override
protected void onProgressUpdate(Integer... values) {
if(listener != null) listener.onProgressUpdate(values[0]);
}
@Override
protected void onPostExecute(Boolean result) {
if(!result) {
if(listener != null) listener.onDownloadFailure(msg);
return;
}
if(listener != null) listener.onDownloadComplete(saveTo);
}
}
Create main activity [cci]src/MainActivity.java[/cci]
This is our main activity that will inflate the [cci]res/layout/activity_main.xml[/cci] to build our main user interface. The activity will create and execute [cci]DownloadTask[/cci] object when Start Button is clicked. Our activity also implements the [cci]DownloadListener[/cci] and set itself as a listener to [cci]DownloadTask[/cci] object. The [cci]DownloadTask[/cci] object will call the listener method implementation in the activity when the progress updated, download failure and when download completed.
Adding permission to [cci]AndroidManifest.xml[/cci]
This simple application has two main features:
Connecting to internet to download a file
Save the file into sdcard storage
In order to our application runs well, we must add [cci]uses-permission[/cci] in our [cci]AndroidManifest.xml[/cci] related to above features. Add the following lines into [cci]AndroidManifest.xml[/cci]:
List View is an element that displays a collection of items in single column direction. It has an internal vertical scroll bar that enable user to scroll if it’s height bigger than display height. The type of single item in the list is any of java object.
[cci]ListView[/cci] needs an adapter to works. This adapter behaves as a data resources for the list. The adapter also defines how each items in the list is displayed. The adapter is attached to the list via [cci]setAdapter[/cci] method on the [cci]ListView[/cci] object. There are two commons used adapters:
Array Adapter: An adapter that is designed to work with arrays data resources.
Cursor Adapter: An adapter that is designed to handle database related data.
This tutorial will focuses on array adapter.
Simple Array Adapter
A simple array adapter is an array adapter that is built using array of string as items. The array of string is passed to the constructor of [cci]ArrayAdapter[/cci] object.
List<String> apps = new ArrayList<String>();
apps.add("Twitter");
apps.add("Whatsapp");
apps.add("Facebook");
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, apps);
The constructor of array adapter have 3 arguments:
context: this is the application context
layout resource id: the layout resource id for item view
array items: this is array object for items
We will attach the created adapter into the list by using [cci]setAdapter[/cci] method on [cci]ListView[/cci] object.
List Activity
[cci]ListActivity[/cci] is a subclass of [cci]Activity[/cci] that will make our work with [cci]ListView[/cci] easier. [cci]ListActivity[/cci] has internal implementation method that is related to [cci]ListView[/cci]. You must have list view object with id is [cci]android:id/list[/cci] in the layout file to use List Activity.
Now we will create a sample list view application using simple array adapter. Open your Eclipse IDE and create new android project by selecting menu: File -> New -> Android Application Project. Fill out required fields.
Run your project, your list view will be displayed like image below:
Simple Android List View
Customize Array Adapter
By default, array adapter displays a [cci]TextView[/cci] for each items and set the text of it by calling [cci]toString[/cci] method of item object. We can customize the default display of array adapter by overriding [cci]getView[/cci] method.
For a demo, we will modify previous project and use custom array adapter:
Create new java class: [cci]Application.java[/cci].
This class represents a single object of list item.
package com.sj.customlistview;
public class Application {
private String title;
private long totalDl;
private int rating;
private String icon;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public long getTotalDl() {
return totalDl;
}
public void setTotalDl(long totalDl) {
this.totalDl = totalDl;
}
public int getRating() {
return rating;
}
public void setRating(int rating) {
this.rating = rating;
}
public String getIcon() {
return icon;
}
public void setIcon(String icon) {
this.icon = icon;
}
}
Create new xml file: [cci]app_custom_list.xml[/cci]
This file defines a view for list item
Gravity is an android method for aligning view in a layout. There are two kinds of gravity, gravity and layout gravity. Basically a gravity is set in xml layout files, but you can also set a gravity of any view in java source code. To set gravity in xml use [cci]android:layout_gravity[/cci] and [cci]android:gravity[/cci] attributes. The values of both attributes is combination of the following constants:
top
: Push object to the top of its container, not changing its size.
bottom
: Push object to the bottom of its container, not changing its size.
left
: Push object to the left of its container, not changing its size.
right
: Push object to the right of its container, not changing its size.
center_vertical
: Place object in the vertical center of its container, not changing its size.
fill_vertical
: Grow the vertical size of the object if needed so it completely fills its container.
center_horizontal
: Place object in the horizontal center of its container, not changing its size.
fill_horizontal
: Grow the horizontal size of the object if needed so it completely fills its container.
center
: Place the object in the center of its container in both the vertical and horizontal axis, not changing its size.
fill
: Grow the horizontal and vertical size of the object if needed so it completely fills its container.
clip_vertical
: Additional option that can be set to have the top and/or bottom edges of the child clipped to its container’s bounds. The clip will be based on the vertical gravity: a top gravity will clip the bottom edge, a bottom gravity will clip the top edge, and neither will clip both edges.
clip_horizontal
: Additional option that can be set to have the left and/or right edges of the child clipped to its container’s bounds. The clip will be based on the horizontal gravity: a left gravity will clip the right edge, a right gravity will clip the left edge, and neither will clip both edges.
start
: Push object to the beginning of its container, not changing its size.
end
: Push object to the end of its container, not changing its size.
android:gravity attribute
[cci]android:gravity[/cci] will set alignment to the content of a view. This aligment will only take effect if size of view is bigger than view’s content. Maybe you got confuse, what is the different between view and view content. Consider a button view below.
Button View
As you can see from image above, the button view is the rectangle boundary of a button, while the content of the button view is the text “button” it self.
Now, we will align the content of the button to bottom right of the button. To align content to bottom right we add [cci]android:gravity=”bottom|right”[/cci] attribute.
[cci]android:layout_gravity[/cci] is used to align view child to its parent. Note that this attribute will only take effect if the parent is [cci]LinearLayout[/cci] and the size of child smaller than parent size.
Now we will align a button to the right of parent. To do this, we must add [cci]android:layout_gravity=”right”[/cci] attribute.
Relative Layout is an android view group to align all childrens relative to other view or its parent. Relative layout give you flexibiliy to place childs wherever you want. In the previous example, I have give some basic example of Relative Layout. Now, I will give you how to create a more complex relative layout example.
Our goal is to create layout like this:
Advance relative layout example
See the following step by step to create above layout:
1. Aligning child to top left of parent
Actually, by default every childs is aligned to top left of parent in relative layout. So we needn’t add any special attribute to align chilc in top left of parent. But you can align child to top left of parent by adding [cci]android:layout_alignParentLeft=”true”[/cci] and [cci]android:layout_alignParentTop=”true”[/cci] attributes.
To align child in top right of parent, add the following attributes [cci]android:layout_alignParentRight=”true”[/cci] and [cci]android:layout_alignParentTop=”true”[/cci].
To align child in bottom left of parent, add the following attributes [cci]android:layout_alignParentBottom=”true”[/cci] and [cci]android:layout_alignParentLeft=”true”[/cci].
To align child in bottom right of parent, add the following attributes [cci]android:layout_alignParentBottom=”true”[/cci] and [cci]android:layout_alignParentRight=”true”[/cci].
This is our center child and you must give it an [cci]id[/cci] as our other 4 childs aligned relative this child. To align a child center of the parent, add the following attribute [cci]android:layout_centerInParent=”true”[/cci]. This attribute will align our child center to the parent, vertically and horizontally.
To align child in top left of the center child, add the following attributes [cci]android:layout_toLeftOf=”@id/button5″[/cci] and [cci]android:layout_above=”@id/button5″[/cci].
To align child in top right of the center child, add the following attributes [cci]android:layout_toRightOf=”@id/button5″[/cci] and [cci]android:layout_above=”@id/button5″[/cci].
8. Align child in bottom right of the center child
To align child in bottom right of the center child, add the following attributes [cci]android:layout_toRightOf=”@id/button5″[/cci] and [cci]android:layout_below=”@id/button5″[/cci].
To align child in bottom left of the center child, add the following attributes [cci]android:layout_toLeftOf=”@id/button5″[/cci] and [cci]android:layout_below=”@id/button5″[/cci].