Sunday, November 21, 2010

Finding the users language settings via code

We've seen before how easy it is to reference difference resources based on the users language settings, but that was more-or-less managed by the Android framework itself.

What if you want to programmatically make decisions in your code based on what the user's language and local settings are?

Turns out, it's very easy, and here's how:
(this example assumes you have a TextView in your layout.main called tvLocale)

package com.Bluemongo.LanguageTest;

import java.util.Locale;

import android.os.Bundle;
import android.widget.TextView;

public class LanguageTest extends Activity 
 public void onCreate(Bundle savedInstanceState) 
  TextView tvLocale = (TextView) findViewById(;
       if (Locale.getDefault().getLanguage().equals("en")) 
        {tvLocale.setText("you're speaking English");}

        if (Locale.getDefault().getLanguage().equals("de")) 
        {tvLocale.setText("you're speaking German");}
        if (Locale.getDefault().getLanguage().equals("fr")) 
        { tvLocale.setText("you're speaking French");}   

.. Told you it was easy.

Sunday, October 24, 2010

Wine Advisor, my first paid app is now available on the Android Market.

Wine Advisor, my first paid app is now available on the Android Market. And it's only $1.99! Bargain!

Discover what wines go with your favourite foods with Wine Advisor, the premier wine & food pairing assistant on Android.

Choose your food and find wine pairing suggestions, including a brief description of the wine. 

Great in restaurants or the grocery store. 

10,000 possible combinations!


If you can, please support this blog and consider buying it, I'll be your best friend and answer all your Android questions first  :)

Thursday, October 14, 2010

Spinner down arrow stretching?

.. Styling the inner and outer views of a Spinner individually.

I was working with a Spinner with a lot of rows fetched from a database, and wanted to put a bit of padding around each item to make it easier for the user to select them.

So I went into my res\layout\spinner_view_row.xml (which controls how the Spinner rows display) and added this:


Then, when I went and re-ran my app, what used to look like this:

.. now looks like this:

.. Ooops. 

Looks like a condom doesn't it. Not what I was trying to achieve, really. If I made the padding large enough, it will also look like that before I've even selected anything.

Not what I wanted at all.

But I do want that padding around each item in my Spinner, otherwise my users will have too much trouble choosing items from my latest super-dooper, take-the-world-by-storm, #1 in the world market app, and it might not stay #1 for long at all.

Luckily, the answer is really, really simple.

You might recogise the below as the piece of code that binds a cursor from the database (containing all the items we want to display), to the xml view spinner_view_row, located at  res\layout\spinner_view_row.xml (this is the xml file in which we put the extra padding, above).

  final SimpleCursorAdapter ingredientAdapter =
  new SimpleCursorAdapter(this, android.R.layout.simple_spinner_item, ingredientsCursor, from, to); 


All we need to do to avoid the stretchy condom spinner arrow is to define another xml view in res\layout\ and call it something like spinner_view_closed, then paste into it the same code that you have in spinner_view_row.
Simply then customise this xml to have less padding, or a smaller text size for instance, then replace the reference to
with a reference to this new xml file, like this:

  final SimpleCursorAdapter ingredientAdapter =
  new SimpleCursorAdapter(this, R.layout.spinner_view_row_closed, ingredientsCursor, from, to); 


.. and your new Spinner will look like this when open:

.. and this when closed.

Easy eh?
.. Told you so.

Monday, October 4, 2010

Android Market expands: More Countries, More sellers, More buyers

Support for paid Android application sales is now expanded to developers in 29 countries, with the addition of Argentina, Australia, Belgium, Brazil, Canada, Denmark, Finland, Hong Kong, Ireland, Israel, Mexico, New Zealand, Norway, Portugal, Russia, Singapore, South Korea, Sweden, Switzerland and Taiwan.

In addition, Android Market users from 32 countries will be able to buy apps, with the addition of Argentina, Belgium, Brazil, Czech Republic, Denmark, Finland, Hong Kong, India, Ireland, Israel, Mexico, Norway, Poland, Portugal, Russia, Singapore, Sweden, and Taiwan.

.. Get programming people!

Official blurb here.

Using EditText's inputType to control what type of keyboard is shown

As software developers, there are many circumstances in which you'll want to limit the input options available to your users. We've all seen situations along the lines of the person who enters 'two' in a field where we've only been expecting the number 2. Oh how that screws things up! Oh the laughs we've had eh?

Fortunately, in Android it's easy to gently shepherd our precious users to input the sort of data we're expecting, and we do that with the editText's inputType attribute.

You can set your editText inputType as ‘Phone’ for example, and the user can able to type only numbers. If it is ‘Time’ it will allow only time related characters to be entered. Handy eh?

There are many options, and I've included (what I think is) all of them at the end of this post for your pleasure.

In the meantime, here are some examples that will hopefully illustrate this option:

        <EditText android:id="@+id/etWidth1"

notice the capitalised first letter of the each sentence, that happens automatically!

        <EditText android:id="@+id/etWidth1"

        <EditText android:id="@+id/etWidth1"
ok, so nothing special to see here..

        <EditText android:id="@+id/etWidth1"

        <EditText android:id="@+id/etWidth1"

Remember, limiting the allowable input characters is only one part of good design.

You still need to run a sanity check on all fields that allow the user to enter data.

This is absolutely essential in many, many situations. Do a google search for 'sql injection' for more information on how unsafe fields can result in your entire system being vulnerable.

Here is (what I think is) the full list of EditText InputTypes available to you :


Sunday, August 1, 2010

Using spinner.setSelection & finding the spinner doesn't show the selected item when closed?

Ok, I've just spent a couple of hours trying to figure this out, and now I have, I thought I'd share the incredibly simple solution with you.

The issue: I was needing to set a Spinner's selected item via code, but found when calling the Spinner's setSelection method and passing in the position to set it to, something odd would happen, the closed spinner would appear blank, yet, when clicking on it, the item I've asked to be selected would be correctly located at the top of the spinner.

It looks like a Spinner is not told to redraw when using .setSelection(position), what you have to do is call .setSelection(int position, boolean animate) unless you want your selection to happen silently behind the scenes.

Odd, but easily sorted out.

The incredibly simple solution:

This won't show the fact that the Spinner selection has been set:


This will:

spnIngredients.setSelection(pos, true);

Hope that helps someone out there.
.. Happy Spinning.

Monday, July 12, 2010

Google App Inventor: Android for Beginners for absolute beginners!

Today Google announced a simple-to-use DIY app maker called Google App Inventor.

Google App Inventor brings Android development to non-programmers, employing a design scheme that relies on visual blocks rather than writing pages of code, the App Inventor -- In true Google style, still in Beta, of course -- has functions for just about anything you can do with an Android handset, including access to GPS and phone functionality.

I can imagine this would be fantastic in classrooms.

more information here:
complete this form to apply for access:

Tre Cool!

Tuesday, June 29, 2010

How to tile a background image in Android

For one of the apps I'm working on I wanted to have a nice pixel pattern tiled behind my widgets.
After a little bit of hunting around I found this tutorial, and I thought I'd clean up the lessons within and show you how.

Here's the contents of my main.xml layout file,

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=""

which is referenced in code in the standard way like this:

public void onCreate(Bundle savedInstanceState) {
...// (rest of onCreate method continues here..)

Now note this line:


What's going on there?
.. Glad you asked!

Here's a quick screenshot of the contents of one of my drawable folders in my project:

What is this

Well, here's the contents of that file here:

android:dither="true" />

Can you see what's going on?
Backrepeat.xml defines an instance of the BitmapDrawable class, and that class references our simple scale1.jpg, located in the drawable-hdpi folder.

Simply by adding the:

    android:dither="true" />

line in bold, we are able to achieve results such as this:

Easy isn't it?

One thing to keep in mind is that you should have folders drawable-hdpi, drawable-mdpi & drawable-ldpi, you'll need to add this backrepeat.xml file and the relevant images to each of these to allow this functionality in high, medium and low dpi (dots per inch) screen sizes.


Saturday, June 19, 2010

Localisation & Internationalisation on Android, the easy way

You often hear about Internationalisation (internationalization in US English, or i18n for short), and Localisation (Localization in US English, or L10n for short) in software development circles... ever wonder what that's all about?

Of course you do.

Definitions vary, but the basic idea is generally easily summarised:
  • Internationalisation is the process of designing a software application so that it can be adapted to various languages and regions without engineering changes.
  • Localisation is the process of adapting internationalized software for a specific region or language by adding locale-specific components and translating text.

These two terms usually go hand-in-hand as the term 'globalisation'. See?
.. Course you do.

Each language is given a language code such as 'en-au' for Australian English, or 'en-us' for American English. These language codes are two-letter lowercase ISO language codes (such as "en") as defined by ISO 639-1.
But how do we use this? And how can we easily apply these concepts to our Android programming?

.. Good question!

Best practices in Android suggests defining all your string resources in a 'strings.xml' file (you're doing this already, right?) and placing that file in the 'res\values' folder in your project.

Localisation in Android is as simple as creating a new version of this file and folder, renaming the 'values' folder to 'values' + the language code you wish to support.

For example, all your Italian translations would be located in 'res\values-it\strings.xml', your Chinese translations in 'res\values-zh\strings.xml' as seen here:

If you don't happen to have a friend from whatever country you're trying to translate your app for, just use Google translate.

Once you're done your app is one simple step away from global domination.

All you need to do is copy those freshly translate strings back into a strings.xml file in Eclipse, and, as long as the folder the strings.xml file is located in has the name of 'values' + the language code you're wishing to support, magically any user who has their phone locale set to a locale that uses that language, your translated strings will be used.

No code changes are required.

Handy eh?

Sunday, June 6, 2010

My first App is now available on the Android market, free.

Aspect Ratio Calculator is a simple tool that makes it easy to calculate the dimensions to resize an image.

Great for graphic designers, or anyone resizing images for blogging, it's available in Spanish, Russian, Portuguese, Chinese & Italian.

.. And of course, English ;)

Sunday, April 25, 2010

Book Review: Professional Android 2 Application Development

Professional Android 2 Application Development (Wrox Programmer to Programmer)

Written by an Android authority, this up-to-date resource shows you how to leverage the features of Android 2 to enhance existing products or create innovative new ones.

Serving as a hands-on guide to building mobile apps using Android, the book walks you through a series of sample projects that introduces you to Android's new features and techniques.

It is perhaps one of the most in-depth Android books available, and is also very regularly updated, currently covering Android SDK 2.1 r1.

The Book's author, Reto Meier is a software developer who has been involved in Android since the initial release in 2007. He is an Android Developer Advocate at Google.

Monday, April 19, 2010

Writing Real-Time Games for Android - Google I/O 2009

Do vertex arrays keep you up at night? Do you have nightmares involving frame rates and event loops? If so, this session might have the cure for your condition.

Chris Pruett will discuss the game engine that he developed, using it as a case study to explain the common pitfalls and best practices for building graphics-intensive applications. You'll learn how to properly pipeline game and rendering code, manage drawing surfaces, and incorporate 2D and 3D graphics cleanly.

Tuesday, April 13, 2010

Some notes about Android Context

Context is an interface to global information about an application environment. It's an abstract class whose implementation is provided by the Android system.

Context allows access to application-specific resources and classes, as well as calls for application-level operations such as launching activities, broadcasting and receiving intents, etc.

All the widgets receive a Context parameter in their constructor. In a regular Android application, you usually have two kinds of Context, Activity and Application. It's usually an Activity Context that the developer passes to classes and methods that need a Context.

Basically the Application context is associated with the Application and will always be the same throughout the life cycle of your app, where as the Activity context is associated with the activity and could possible be destroyed many times as the activity is destroyed during screen orientation changes and such.

In particular you should be careful when dealing with anything that deals with the GUI that requires a Context. For example, if you pass the application Context into the LayoutInflator you will get an Exception. It's good practice to use an Activity's Context within that Activity, and the Application Context when passing a context beyond the scope of an Activity to avoid memory leaks.

Here's a quick snippet showing how you can find both the Activity Context and the Application Context:

public class MyActivity extends Activity {
public void aMethod() {
Context actContext = this; /*returns the Activity Context since Activity extends Context.*/

Context appContext = getApplicationContext(); /*returns the context of the single, global Application object of the current process. */

Button btnGoToFirstAct = (Button) findViewById(;
Context vwContext = btnGoToFirstAct.getContext(); /*returns the context of the View. */

When run in the debugger, you can see the results of this:

 Notice that the vwContext in this case also returns the Activity Context.

Hope that helps answer some questions. Drop me a message in the comments if you have anything to add.

Sunday, April 11, 2010

Learn what it takes to make a good Android app great.

Jason, John, and David, mobile industry veterans from Hands-On Mobile, present a technical overview of ways to improve your Android applications stickiness, boost adoption, engage users, and increase monetization and ROI.

This event was hosted by The San Francisco Android User Group at CBS Interactive in San Francisco on August 27th, 2009. The event was sponsored by Hands-On Mobile and organized by Marakana Inc.

Learn how to develop for Android, Beyond HelloWorld

This is a nice, long (2hrs) video, demonstrating many aspects of creating a simple Android application from scratch. Definitely worth checking out if you've got the time.

Sunday, April 4, 2010

How to Make your Android UI Fast and Efficient - video from Google I/O 2009 with Romain Guy

Here a video from Google I/O 2009 with Romain Guy from Google.

"Learn practical tips, techniques and tricks for making your Android applications fast and responsive. This session focussed on optimizations recommended by the Android framework team to make the best use of the UI toolkit."

.. Very interesting stuff. I would really encourage everyone to watch this.
Covers: Adapters, View & Layouts, Backgrounds & images, memory allocation and Drawing & invalidating.

Tuesday, March 16, 2010

Default text for an EditText? Here's a Hint

Sometimes it can be a nice idea to put default values in an EditText to let your users know what sort of information you're wanting them to enter.

What I had been doing previously was setting the .text value of the EditText to some default value, then clearing it onClick, after checking if the value was still the default, like this:

etName.setOnClickListener(new OnClickListener() {

String name = etName.getText().toString();
String origVal = getResources().getText(R.string.NameDefault).toString();

public void onClick(View v) {



Here's my String resource, stored in res/strings.xml as used above:

<?xml version="1.0" encoding="utf-8"?>

<string name="NameDefault">Enter your name</string>

But there is another, easier way, and it's called a Hint.

Simply by adding the below, bold attribute into my xml layout, my EditText by default contains a default string, which only exists when the EditText is empty.

It's all done for me!

.. here is my layout xml, note the android:hint line:

<EditText android:id="@+id/etName"

Saturday, March 6, 2010

Handling Button clicks in a ListView Row

Lets say you have a spinner widget, like the one we created in our 'colours' example, and you wanted to put a button on each row of your spinner for your users to click (everyone loves clicking buttons, right?).

You might have a layout a bit like this simple one below:

<LinearLayout android:id="@+id/LinearLayout01"

 <TextView android:text="this is a row"
 <Button android:text="Click me!"


.. Containing just a textView and a Button View.

A listView with textual, non-clickable views in it responds to Click events via the OnItemClickListener event.

But once you put a button in the ListView, this event no longer fires.

So how do you capture the button's click event, and find what row in your ListView a clicked button is located in?

You may have noticed this android:onClick="myClickHandler"> in our layout above..
What this does is tie every click of every instance of that button, in every row of our ListView to one single handler, located in the code of our ListActivity class below:

    public void myClickHandler(View v) 
        //reset all the listView items background colours 
        //before we set the clicked one..

        ListView lvItems = getListView();
        for (int i=0; i < lvItems.getChildCount(); i++) 
        //get the row the clicked button is in
        LinearLayout vwParentRow = (LinearLayout)v.getParent();
        TextView child = (TextView)vwParentRow.getChildAt(0);
        Button btnChild = (Button)vwParentRow.getChildAt(1);
        btnChild.setText("I've been clicked!");
        int c = Color.CYAN;

In this case, the View v being passed in as a parameter is our button.
We get the parent of our button, being careful to cast it as a LinearLayout (have another look at the xml if you're not sure why), and then simply set the background colour of our Layout Row.

Don't forget to call .refreshDrawableState(); on your vwParentRow or it will never redraw and you won't see your nice colour change.

.. Tada!

Update: Hi everyone, thanks for all the interest, here's a link to the full project zipped.
Updated Update: Here's another link, and another, and another.

I've also updated the above myClickHandler to loop through the other items in the ListView and reset them to a default colour, in this case blue, to make it a bit more obvious what's going on. Hope that helps.

Thursday, February 18, 2010

How to create Status Bar Notifications

A status bar notification is used to notify the user of a system event, like an sms being received or a new device being detected, without interrupting the user from whatever other task they might be doing with their phone.

The status bar area is located at the top of the screen and the user can pull this area to expand it, and show a history of notifications.

If a Notification has been setup to include an enclosed Intent, selecting that particular notification in this expanded view can fire the Intent, taking the user to an Activity screen of the related application, or do any of the many other things that Intents can do.

You can also configure the notification to alert the user with a sound, a vibration, and flashing lights on the device.

A background Service should never launch an Activity on its own in order to receive user interaction. The Service should instead create a status bar notification that will launch the Activity when selected by the user.

A status bar notification should be used for any case in which a background Service needs to alert the user about an event.

Here is a simple method that creates and displays a notification when passed a string msg :

public void displayNotification(String msg)
NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
Notification notification = new Notification(R.drawable.icon, msg, System.currentTimeMillis());

// The PendingIntent will launch activity if the user selects this notification
PendingIntent contentIntent = PendingIntent.getActivity(this, REQUEST_CODE, new Intent(this, ExpandNotification.class), 0);

notification.setLatestEventInfo(this, "Title here", ".. And here's some more details..", contentIntent);

manager.notify(NOTIFICATION_ID, notification);


.. Which you can call simply like this:

displayNotification("Hi, I'm a Statusbar Notification..");

.. Easy, isn't it?

Sunday, February 14, 2010

Want to display a quick message to your users? Use some Toast!

A toast is a notification view that contains a quick little message for the user. All it does is display the message, it's not interactive at all.

The toast class helps you create and show those.

When this view is shown to the user, it appears to float over the application. It will never receive focus as the user may be in the middle of typing something else. The idea is to be as unobtrusive as possible, while still showing the user the information you want them to see. Two possible examples are a volume control, and a brief message saying that your settings have been saved.

The easiest way to use this class is to call one of the static methods that constructs everything you need and returns a new Toast object.

A piece of toast is typically a simple text message, an image, or a combination of text and image.
You don't have control on the toast duration. There are only two states LENGTH_LONG and LENGTH_SHORT.

For this example we have added an image to one of the drawable folders under 'res' in our project, we refer to it simply like this:


Our image is actually called flash.png, note that we don't need to include the 'png' extension in our Android code, it already knows what we're talking about ;)

Here are 3 methods, demonstrating the above.

First, just show an image:

private void imageToast()
Toast toast = new Toast(getApplicationContext());
ImageView view = new ImageView(getApplicationContext());

This method just displays a text toast:

public void textToast(String textToDisplay) {
Context context = getApplicationContext();
CharSequence text = textToDisplay;
int duration = Toast.LENGTH_SHORT;

Toast toast = Toast.makeText(context, text, duration);
toast.setGravity(Gravity.TOP|Gravity.LEFT, 50, 50);;

.. And this method displays a Toast that contains both an image and text:

public void textAndImageToast(String textToDisplay)
Toast toast = Toast.makeText(getApplicationContext(), textToDisplay, Toast.LENGTH_LONG);
View textView = toast.getView();
LinearLayout lay = new LinearLayout(getApplicationContext());
ImageView view = new ImageView(getApplicationContext());

You can call each of these like this:

textToast("This is a text toast");

textAndImageToast("This is a text and image toast");

And here are the results:

A text Toast

A text & image Toast

this is an image Toast

Here is the same image Toast with default Gravity for better demonstration purposes

Hope that makes sense.
.. Till next time, happy coding :)

Monday, February 1, 2010

How to populate a Spinner widget from a database

Yesterday we saw how to populate a Spinner widget from an Array, and today, as promised, I'll show you how to populate a Spinner widget from a database.

This tutorial assumes that you're using the same code we used previously (link above), essentially the only differences are that we're using a different type of Adapter (a SimpleCursorAdapter this time) and populating it with the results of a query from a database table, and we're using a separate layout item to put our colour names

Here is our new layout, called db_view_row.xml:

<LinearLayout android:id="@+id/LinearLayout01"

<TextView android:text=""

put this file in your res/layout directory in your project.

Let's assume for this example that you've already populated your database table with the same list of colours that we used previously.

Here's the statement to create our table structure:

CREATE TABLE "colours" (
"colourName" TEXT NOT NULL

In our database adapter class we have a method called fetchAllColours(), which has the responsibility (probably no surprises here) of fetching all our colours ;).

At the top of our class we declare some static variables we're going to use :

public class TestDBAdapter {

public static final String KEY_TITLE = "colourName";
public static final String KEY_ROWID = "_id";

// of class continues from here..

Here is this method also from our TestDBAdapter class:

public Cursor fetchAllColours()
if (mDb == null)

/* here we check if our db exists as the connection might have been closed unexpectedly... and open it if it doesn't already exist*/

String tableName = "colours";

return mDb.query(tableName, new String[] { KEY_ROWID, KEY_TITLE}, null, null, null, null, null);


... which returns a database Cursor to our method below..

private void fillData() {
Cursor coloursCursor;
Spinner colourSpinner = (Spinner) findViewById(;
coloursCursor = thisTestDBAdapter.fetchAllColours();

/*Create an array to specify the fields we want to display in the list (only the 'colourName' column in this case) */

String[] from = new String[]{TestDBAdapter.KEY_TITLE};

/* and an array of the fields we want to bind those fields to (in this case just the textView 'tvDBViewRow' from our new
db_view_row.xml layout above) */

int[] to = new int[]{};

Now create a simple cursor adapter.. */

SimpleCursorAdapter colourAdapter =
new SimpleCursorAdapter(this, R.layout.db_view_row,
coloursCursor, from, to);

/* and assign it to our Spinner widget */


Update: Due to popular demand, here is a project that demonstrates this concept:
Spinner from Database example.

.. Let me know if you're having any access issues, it's just hosted publicly from my google docs.

I've learnt my lesson, I'm going to be including an example project with all future posts :)

Thanks for your support

This site has only been in existence for 6 weeks, I just wanted to say thankyou for visiting, wherever you are!


Please feel free to post comments on anything you see, and if you have any suggestions for articles, just let me know.

Sunday, January 31, 2010

How to populate a Spinner widget from an Array

Lets say we have an Array of colours, defined in a xml file in our res folder in our Eclipse project, like below.

<?xml version="1.0" encoding="utf-8"?>
<string name="hello">Hello World, droidTest1!</string>
<string name="app_name">droidTest1</string>

<string-array name="colours">

Spinners are Android's implementation of a dropdown menu, of sorts.
How do we insert these values into a spinner widget?

First, we need to create a layout for our Spinner widget, so it has a user interface.
We could do this is code, but the more accepted method is to define our layouts for Android applications in XML files, located in our res/layout folder in our project.







Then we create an instance of the Spinner class,

Spinner colourSpinner = (Spinner) findViewById(;

Next we create an ArrayAdapter to wrap our xml array (Array of colours) and we put some pre-defined styles.

ArrayAdapter adapter = ArrayAdapter.createFromResource( this, R.array.colors, android.R.layout.simple_spinner_item); adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

And we set the ArrayAdapter to our instance of the Spinner class:

And when we run our application:

The closed Spinner Widget

.. When selected shows us out colour options.

Aaah.. Sweet Androidy Success!


Saturday, January 30, 2010

Android Adapters: an introduction

An Adapter object acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items. The Adapter is also responsible for making a View for each item in the data set.

An AdapterView is a view whose children are determined by an Adapter.

Some examples of AdapterViews are ListView, GridView, Spinner and Gallery.

There are several types or sub-classes of Adapter:

ListAdapter: Extended Adapter that is the bridge between a ListView and the data that backs the list. Frequently that data comes from a Cursor, but that is not required. The ListView can display any data provided that it is wrapped in a ListAdapter.

ArrayAdapter: A ListAdapter that manages a ListView backed by an array of arbitrary objects. By default this class expects that the provided resource id references a single TextView.

CursorAdapter: Adapter that exposes data from a Cursor to a ListView widget. The Cursor must include a column named "_id" or this class will not work.

HeaderViewListAdapter: ListAdapter used when a ListView has header views. This ListAdapter wraps another one and also keeps track of the header views and their associated data objects.
This is intended as a base class; you will probably not need to use this class directly in your own code.

ResourceCursorAdapter: An easy adapter that creates views defined in an XML file. You can specify the XML file that defines the appearance of the views.

SimpleAdapter: An easy adapter to map static data to views defined in an XML file. You can specify the data backing the list as an ArrayList of Maps. Each entry in the ArrayList corresponds to one row in the list.

SimpleCursorAdapter: An easy adapter to map columns from a cursor to TextViews or ImageViews defined in an XML file. You can specify which columns you want, which views you want to display the columns, and the XML file that defines the appearance of these views.

SpinnerAdapter: Extended Adapter that is the bridge between a Spinner and its data. A spinner adapter allows to define two different views: one that shows the data in the spinner itself and one that shows the data in the drop down list when the spinner is pressed.

WrapperListAdapter: List adapter that wraps another list adapter. The wrapped adapter can be retrieved by calling getWrappedAdapter().

Android applications: Components and Structure

Android extends the standard views/data model, providing a new model that is suitable for equipment activated at all times.

The structure of an Android application is defined as follows:

The file AndroidManifest.xml

This defines the components of the application and their relationships. It gives the permissions to application as to what it can do with users. It can also give permission to components of the application.

The views (Class android.view.View)

The interface of a program for Android is a tree of views.

Activity ( class)
This is something that the user can do, translated into program. It corresponds to a screen, but can have multiple views.

Intent (android.content.Intent class)
Describes an action which must be performed.

Service ( )
Program that operates in background.

Content Provider (android.content.ContentProvider class)
Encapsulates data and provides them commonly to several programs.

Notification ( and classes)
Class which informs the user about what is happening.

Besides components, there are also resources that can be XML files, image files as jpeg, etc. These use the android.content.Resources interface and are stored in the res directory.

Components of an Android application

Each component is included in a list stored in the manifest file AndroidManifest.xml of each application.


An activity corresponds to a screen. If an application is composed of several screens, it has an activity for each screen. Each activity is a class that extends the base class Activity. It has a graphical user interface made of views, and it responds to events. When you change screen, a new activity is launched.
It can return a value. For example, if an activity can choose something, text, image, it returns what is chosen.

The graphical interface of an activity is described by a Layout:
- Full screen.
- Float: dialogue or alert.
- None. In this case it works in background and is invisible. It is maked visible by giving it a layout.

Note that the graphical user interface is described in XML as XUL and XAML.


The intents are the goals of applications and are made effective by a new screen. An intent is made up of an action and data that are URI.

Examples of actions: MAIN, VIEW, EDIT, PICK.
If one wants to see a card about a person, an intent is defined. The action is VIEW and the data is the URI which enables access to this card.

IntentFilters describes how the action should apply.

IntentReceiver is an object that responds to external events. It can operate in the application or it can start an application.

Example of intent, view a webpage: VIEW for action and for data


A service is designed to operate independently of the screen, thus of activities. The best example is the music player that can works while moving from one screen to another.

Content Provider

Data stored by a computer program, in the form of files or SQLite databases are private and may not be used by other applications.
But Content Provider may be used to share data among several applications. The interface ContentResolver is the interface that provides data to other objects.


The class defines how an event must be notified to user: displaying an icon, changing state of a led, vibration, or others. While the class sends the message in the form so defined.