Android Trainning Session 2

Fragments

A Fragment is a piece of an activity which enable more modular activity design. It will not be wrong 

if we say, a fragment is a kind of sub-activity

Design Philosophy

Fragments life cycle

Example:    http://examples.javacodegeeks.com/android/core/app/fragment/android-fragments-example/

Toast• A toast provides simple feedback about an operation in a

small popup. It only fills the amount of space required for the message and the current activity remains visible and interactive. For example, navigating away from an email before you send it triggers a "Draft saved" toast to let you know that you can continue editing later. Toasts automatically disappear after a timeout.

• EX:Context context = getApplicationContext();CharSequence text = "Hello toast!";int duration = Toast.LENGTH_SHORT;Toast toast = Toast.makeText(context, text, duration);toast.show();

Dialog• A dialog is a small window that prompts the user to make a decision or

enter additional information. A dialog does not fill the screen and is normally used for modal events that require users to take an action before they can proceed.

Example:

AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());// Add the buttonsbuilder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int id) { // User clicked OK button } });builder.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int id) { // User cancelled the dialog } });// Set other dialog properties...

// Create the AlertDialogAlertDialog dialog = builder.create();

Notification• A notification is a message you can display to the user outside of your application's

normal UI. When you tell the system to issue a notification, it first appears as an icon in the notification area. To see the details of the notification, the user opens the notification drawer. Both the notification area and the notification drawer are system-controlled areas that the user can view at any time.

Services

• A service is an application component that can perform long-running operations in the background and does not provide a user interface. Another application component can start a service and it will continue to run in the background even if the user switches to another application. Additionally, a component can bind to a service to interact with it and even perform interprocess communication (IPC). For example, a service might handle network transactions, play music, perform file I/O, or interact with a content provider, all from the background.

Services life cycle

Implementing a Services

Connecting to the Network• your application manifest must include the following

permissions:– <uses-permission

android:name="android.permission.INTERNET" />– <uses-permission

android:name="android.permission.ACCESS_NETWORK_STATE" />• Choose an HTTP Client:– Most network-connected Android apps use HTTP to send and

receive data. Android includes two HTTP clients: HttpURLConnection and Apache HttpClient. Both support HTTPS, streaming uploads and downloads, configurable timeouts, IPv6, and connection pooling.

– HttpURLConnection => for applications targeted at Gingerbread and higher.

Check the Network Connectionpublic void myClickHandler(View view) { ... ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); NetworkInfo networkInfo = connMgr.getActiveNetworkInfo(); if (networkInfo != null && networkInfo.isConnected()) { // fetch data } else { // display error } ...}

AsyncTask • AsyncTask is an abstract class provided by Android which helps us to

use the UI thread properly. This class allows us to perform long/background operations and show its result on the UI thread without having to manipulate threads.

• AsyncTask has four steps:– doInBackground: Code performing long running operation goes in this

method. When onClick method is executed on click of button, it calls execute method which accepts parameters and automatically calls doInBackground method with the parameters passed.

– onPostExecute: This method is called after doInBackground method completes processing. Result from doInBackground is passed to this method.

– onPreExecute: This method is called before doInBackground method is called.

– onProgressUpdate: This method is invoked by calling publishProgress anytime from doInBackground call this method.

JSON parsing • JSON stands for JavaScript Object Notation.It is an independent data exchange format and is the best alternative

for XML.• Ex:

{ "sys": { "country":"GB", "sunrise":1381107633, "sunset":1381149604 }, "weather":[ { "id":711, "main":"Smoke", "description":"smoke", "icon":"50n" }],"main": { "temp":304.15, "pressure":1009, }}

Broadcast Receiver Broadcast Receivers simply respond to broadcast messages from other applications or from the system itself. These messages are sometime called events or intents. For example, applications can also initiate broadcasts to let other applications know that some data has been downloaded to the device and is available for them to use, so this is broadcast receiver who will intercept this communication and will initiate appropriate action• There are following two important steps to make

Broadcast Receiver works for the system broadcasted intents −– Creating the Broadcast Receiver.– Registering Broadcast Receiver

Creating the Broadcast Receiver:

A broadcast receiver is implemented as a subclass of BroadcastReceiver class and overriding the onReceive() method where each message is received as a Intent object parameter.public class MyReceiver extends BroadcastReceiver { @Override public void onReceive(Context context, Intent intent) { Toast.makeText(context, "Intent Detected.", Toast.LENGTH_LONG).show(); }}

Registering Broadcast Receiver:

An application listens for specific broadcast intents by registering a broadcast receiver in AndroidManifest.xml file. Consider we are going to register MyReceiver for system generated event ACTION_BOOT_COMPLETED which is fired by the system once the Android system has completed the boot process.

public void broadcastIntent(View view){ Intent intent = new Intent(); intent.setAction("com.ex.CUSTOM_INTENT"); sendBroadcast(intent); }

Mainfest.xml :

<application android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <receiver android:name="MyReceiver"> <intent-filter> <action android:name=“com.ex.CUSTOM_INTENT"> </action> </intent-filter

Content Provider • A content provider component supplies data from one application to

others on request. Such requests are handled by the methods of the ContentResolver class. A content provider can use different ways to store its data and the data can be stored in a database, in files, or even over a network.

public class My Application extends ContentProvider {}

Create Content Provider

This involves number of simple steps to create your own content provider.1. First of all you need to create a Content Provider class that extends the

ContentProviderbaseclass.2. Second, you need to define your content provider URI address which will be used to access

the content.3. Next you will need to create your own database to keep the content. Usually, Android uses

SQLite database and framework needs to override onCreate()method which will use SQLite Open Helper method to create or open the provider's database. When your application is launched, the onCreate() handler of each of its Content Providers is called on the main application thread.

4. Next you will have to implement Content Provider queries to perform different database specific operations.

5. Finally register your Content Provider in your activity file using <provider> tag.

Mainfest.xml:

<provider android:name="StudentsProvider" <android:authorities="com.example.provider.College"> </provider>

Data Storage

Android provides several options for you to save persistent application data. The solution you choose depends on your specific needs, such as whether the data should be private to your application or accessible to other applications (and the user) and how much space your data requires.

STORAGE OPTIONS

Data Backup

Android’s backup service allows you to copy your persistent application data to remote "cloud" storage, in order to provide a restore point for the application data and settings. If a user performs a factory reset or converts to a new Android-powered device, the system automatically restores your backup data when the application is re-installed. This way, your users don't need to reproduce their previous data or application settings. This process is completely transparent to the user and does not affect the functionality or user experience in your application.

Location API

Specify App Permissions:

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.google.android.gms.location.sample.basiclocationsample" > <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/></manifest>

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