Pre-Packaged Applications | Android Tutorial for Beginners (Part 4)

There are many applications that can pre-packaged into the android platform that can be reused by custom built applications because of the power of the android design that is based on implicit intents.(See part 3 of this series for implicit intents).

Here we will explore how to invoke the pre-packaged applications from our own through implicit intents. Note that in none of the snippets below, we actually call the pre-packaged or system applications. We just declare intents and pass them to an activity while starting the activity through startActivity() method. However, for each of these intents, the android platform finds the most befitting activity and invokes the same:

1. Call a number

      Intent callNumber = new Intent();

      callNumber.setAction(android.content.Intent.ACTION_CALL);

      callNumber.setData(Uri.parse("tel:9440012345"));

startActivity(callNumber);

This will call the number 9440012345. For calling custom numbers, you could provide the user with a edit text field from which you can access the number and set it to the data above instead of a hard-coded number.

2. Browse the web for a given url:

      Intent searchGivenText = new Intent(Intent.ACTION_WEB_SEARCH);

      searchGivenText.putExtra(SearchManager.QUERY, "Android Examples);

      startActivity(searchGivenText);

This will invoke the Google search engine to search the string "Android Examples" and return the results to you. This too can be generalized to accept a string from the user and set to the intent before starting the activity.

3.  View google maps for a given location

      Intent searchAddress = new Intent(Intent.ACTION_VIEW, 

      Uri.parse("geo:0,0?q=Bangalore"));

startActivity(searchAddress);

This shows the location of Bangalore on Google Maps.

4. View Contacts on the phone

Intent contacts = new Intent();

      contacts.setAction(android.content.Intent.ACTION_VIEW);

      contacts.setData(People.CONTENT_URI);

      startActivity(contacts);

I have created an Android eclipse project which showcases all of these examples by taking inputs from the end user. You can access the same here.

--------
Updated on March 31 2010:

The above example uses Android SDK 1.5 From SDK 1.6 and above, the Contact.People class has been deprecated and we need to use the ContactsContract class. So the line in code
      contacts.setData(People.CONTENT_URI);
has to be replaced by
              contacts.setData(ContactsContract.Contacts.CONTENT_URI);

Here is the complete source code that has been tested with Android SDK 2.1

Implicit Intent | Android Tutorial for Beginners (Part 3)

We have seen in Part 2 how to use Explicit Intents to invoke activities through a very simple example. Now, we will move on to a more interesting concept of Implicit Intents and Intent Filters. 

This requires a little of theoretical understanding before we move on to an example. 

As described earlier, an implicit intent does not name a target component that should act upon the intent. I 

also said that the android platform resolves as to which component is best suited to respond to an Implicit Intent. How does this happen?

Basically, an Intent object has the following information (among other things like Component name, extras and flags) which is of interest for implicit intents:

• Action
  
• Category
  
• Data
  

So, the android platform compares these 3 (action, category and data) to something called "Intent Filters" that are declared by probable target components who are willing to accept Implicit Intent calls.

i.e. Intent Filters are the way of any component to advertise its own capabilities to the Android system. This is done declaratively in the AndroidManifest.xml file.

So here are some important points to remember:

1. Implicit Intents do not specify a target component
   
2. Components willing to receive implicit intents have to declare their ability to handle a specific intent by declaring intent filters
   
3. A component can declare any number of Intent Filters
   
4. There can be more than one component that declares the same Intent Filters and hence can respond to the same implicit intent. In that case the user is presented both the component options and he can choose which one he wants to continue with
   
5. You can set priorities for the intent filters to ensure the order of responses.
   

There are 3 tests conducted in order to match an intent with intent filters:

1. Action Test
   
2. Category Test
   
3. Data Test
   

For more details about them, you may visit the Android developer documentation here.

Finally we shall look at declaring an implicit intent in one activity which will invoke one of the native activities of the platform by matching the intent filters declared by the same.

The complete code for a very simple implicit intent example that has been described in this article is available for download here.

The InvokeImplicitIntent Activity creates an implicit intent object "contacts". This intent object's component is not set. However, the action is set to "android.content.intent.ACTION_VIEW" and the data's URI is set to "People.CONTENT_URI". 

Such an intent matches with the intent filter declared by the view contacts native activity.

So, when you run this application, it displays the native UI for viewing the existing contacts on the phone!

Here is the relevant piece of code for the same:

           Button viewContacts = (Button)findViewById(R.id.ViewContacts);

        
            viewContacts.setOnClickListener(new OnClickListener() {
            
             public void onClick(View v) {
              Intent contacts = new Intent();
              contacts.setAction(android.content.Intent.ACTION_VIEW);
              contacts.setData(People.CONTENT_URI);
              startActivity(contacts);
             }
            });

In this manner many of the native applications can be seamlessly invoked as one of the activities in our applications through implicit intents.

---------------------------------------------------------------------------------------------------------
Updated on 31st March 2010:
The above example uses Android SDK 1.5.
From SDK 1.6 and above, the Contact.People class has been deprecated and we need to use the ContactsContract class. So the line in code
       contacts.setData(People.CONTENT_URI);

has to be replaced by

       contacts.setData(ContactsContract.Contacts.CONTENT_URI);

Here is the complete source code that has been tested with Android SDK 2.1

Explicit Intent | Android Tutorial for Beginners (Part 2)

Having introduced you to the basic anatomy of an android application in the Part 1 of the series, I would like to show you an example where communication between 2 activities happens through an intent.

However, just one more detail to be introduced as promised and that is -

There are 2 types of intents that Android understands.

1. Explicit Intent

2. Implicit Intent

In an Explicit intent, you actually specify the activity that is required to respond to the intent. In other words, you explicitly designate the target component. This is typically used for application internal messages.

In an Implicit intent (the main power of the android design), you just declare an intent and leave it to the platform to find an activity that can respond to the intent. Here, you do not declare the target component and hence is typically used for activating components of other applications seamlessly

Note: Here for simplicity sake I tell an activity responds to an intent, it could as well be other types of components.

Now I will jump into the example which you can download from here:

This example has 2 activities:
1. InvokingActivity
2. InvokedActivity
The InvokingActivity has a button "Invoke Next Activity" which when clicked explicitly calls the "InvokedActivity" class.
The relevant part of the code is here:

        Button invokingButton = (Button)findViewById(R.id.invokebutton);
        invokingButton.setOnClickListener(new OnClickListener() {
        
         public void onClick(View v) {
         Intent explicitIntent = new Intent(InvokingActivity.this,InvokedActivity.class);
         startActivity(explicitIntent);
         }
        });

As explained in part 1 of the series, this is very much like an API call with compile time binding.

NOTE: The layout for InvokingActivity is defined in main.xml and for InvokedActivity in InvokedActivity.xml. The downloadable example can be opened in Eclipse Ganymede as an android project and can be executed.

In the next part of the series, we will see how to work with implicit intents which also needs us to understand intent-filters. 

Fundamentals | Android Tutorial for Beginners (Part 1)

This is Part 1 of a series of articles I plan to write to simplify the new paradigms introduced by the Android platform for developers.

The part 1 will only define and introduce the fundamental building blocks of Android. Later articles will provide sample code focusing on one aspect at a time, more to drive home to concept than to show any great programming skills.

From a developer's perspective, the fundamental building blocks / components of Android are:

1. Activities

2. Services

3. Broadcast Receivers

4. Content Providers.

The means of communication between the above mentioned components is through

1. Intents

2. Intent Filters

The User Interface elements are by using what are called:

1. Views

2. Notifications

Now, having broadly classified the basics, I would like to give a simple definition for each of them, before we can appreciate the need for each of them.

Activity is the basic building block of every visible android application. It provides the means to render a UI. Every screen in an application is an activity by itself. Though they work together to present an application sequence, each activity is an independent entity.

Service is another building block of android applications which does not provide a UI. It is a program that can run in the background for an indefinite period.

Broadcast Receiver is yet another type of component that can receive and respond to any broadcast announcements.

Content Providers are a separate league of components that expose a specific set of data to applications.

While the understanding and knowledge of these four components is good enough to start development, the knowledge of the means of communication between the components is also essential. The platform designers have introduced a new conpect of communication through intents and intent filters.

Intents are messages that are passed between components. So, is it equivalent to parameters passed to API calls? Yes, it is close to that. However, the fundamental differences between API calls and intents' way of invoking components is

1. API calls are synchronous while intent-based invocation is asynchronous (mostly)

2. API calls are bound at compile time while intent-based calls are run-time bound (mostly)

It is these two differences that take Android platform to a different league.

NOTE: Intents can be made to work exactly like API calls by using what are called explicit intents, which will be explained later. But more often than not, implicit intents are the way to go and that is what is explained here.

One component that wants to invoke another has to only express its' "intent" to do a job. And any other component that exists and has claimed that it can do such a job through "intent-filters", is invoked by the android platform to accomplish the job. This means, both the components are not aware of each other's existence and can still work together to give the desired result for the end-user.

This dotted line connection between components is achieved through the combination of intents, intent-filters and the android platform.

This leads to huge possibilities like:

1. Mix and match or rather plug and play of components at runtime

2. Replacing the inbuilt android applications with custom developed applications

3. Component level reuse within and across applications

4. Service orientation to the most granular level, if I may say

Now that the concept of intent has been introduced, let me get down to a more formal definition of Intent.

Intent is a bundle of information, a passive data structure that holds an abstract description of the operation to be performed. (or in the case of broadcasts, a description of an event that has happened and is being announced).

There are 2 types of intents which I intend to detail in the next part of this series. Before winding up part 1, I would finally also give you a formal definition of Intent filters.

Intent filters are the means through which a component advertizes its own capabilities to handle specific job/operations to the android platform.

Tips for High Performance Websites

Steve Souders in his website has given 15 tips - some very fundamental ones for creating high performance websites, along with demonstrations of what he says. Very Interesting and useful.

The list is here. Visit his website to actually see the demos.

• Rule 1 - Make Fewer HTTP Requests
• Rule 2 - Use a Content Delivery Network
• Rule 3 - Add an Expires Header
• Rule 4 - Gzip Components
• Rule 5 - Put Stylesheets at the Top
• Rule 6 - Put Scripts at the Bottom
• Rule 7 - Avoid CSS Expressions
• Rule 8 - Make JavaScript and CSS External
• Rule 9 - Reduce DNS Lookups
• Rule 10 - Minify JavaScript
• Rule 11 - Avoid Redirects
• Rule 12 - Remove Duplicate Scripts
• Rule 13 - Configure ETags
• Rule 14 - Make AJAX Cacheable
• Rule 15 - Use Iframes Wisely

He even talks about tools that he has used for some of these tasks, ex. JSmin to minify a script, Dojo compressor to obfuscate a script, etc.

Interestingly he also points that most of the optimization for better performing websites seems to be a front end problem more than a back end one. He has learnt this when he was the chief performance Yahoo! and has published a book "High Performance Web Sites: Essential Knowledge for Front-End Engineers " on the same.

Android - Technically, What Is It?

Android - Technically what is it?

(an overivew of what is Android and its uniqueness is discussed in another post below)


1. It is an operating system for mobile
   
2. Interestingly, it is not yet another OS, but component based
   OS
   
3. It has an integrated Java Virtual Machine
   
4. System interfaces are exposed only through Java libraries
   
5. It is based on the Linux Kernel
   
6. An Android SDK is provided to let developers build applications on top of the OS but not extend the OS itself
   
7. The SDK includes
   
   
   
   • Android packages
     
   • sample files
     
   • Documentation
     
   • A Simulator

The offical site of Android broadly classfies the technical parts of the OS as
consisting of

1. Linux Kernel
   
2. Android Runtime
   
3. Libraries
   
4. Application Framework
   

over which the core applications run as well as the applications developed by anyone using this framework

The Uniqueness of Android – The Mobile Platform from Google

There is a huge furore and expectation in the mobile industry, after the announcement of “Android”, the mobile platform (consisting of an operating system, middleware and key applications), by Google last November. Its ripple effect in the developer community and the services industry is also pretty palpable.

In Google’s typical way, the 10 million dollar awards towards the best android applications had added the required momentum to bring the large developer community into its fold, and at the same time, harvest collective intelligence.

What is so unique about Android?
We have had many mobile OS like the Symbian, Windows Mobile OS, Mac OS X and Linux based Palm Nova, ALP etc, already flooding the market and fragmenting it.
So, why is another OS required?
If we are talking about something very radical, iPhone did it all. It took the market by storm with its mind-boggling features.
With all these in the market, isn’t android late? Still, why the interest?

Market Buy-in

Google has first of all roped in most of the players in the mobile market be it mobile operators, handset manufacturers, mobile application providers or software companies and even some commercialization companies.

The only significant players who are missing from the list for obvious reasons are:
1. Microsoft
2. Apple
3. Nokia
4. Palm
Two Major National US carriers missing are AT&T and Verizon.

Google is planning to keep it open source, the most happening way to get the acceptance in the market

Technically,
1. It is the only OS so far that allows integration / use of the basic phone features with any externally developed mobile application,
2. It is designed to simplify the reuse of components. Any application can publish its capabilities and any other application can use it. Taking the cue from the enterprise world on service oriented architecture, android has built it into its fundamental architecture
3. It is built on the open Linux Kernel
4. It will be open source
5. Mashup-ready: Embed browser and map views directly in your applications

To the End User:
1. Choice will be unlimited. The end user is not tied to using the basic features of the phone as provided by the handset manufacturer. He could use his own choice from any third party provider as the default feature of the phone
2. The ability to seamlessly integrate core and new applications will produce a new generation of unheard-of applications that are going to change the way the mobile would be used. Like for example, the ability to alert friends who are in the vicinity about your presence or the ability to be notified of all the shops that have a product you are looking for, as you enter a mall.
3. The open platform should provide more cheaper and innovative mobile devices and services
4. Application life cycle and automatic process management frees the end user from worrying about what applications are active
5. Location based services and notifications
6. Standard 2d and 3d graphics with optional acceleration
7. High quality audio/video support including H.264 (AVC).
8. Low power operation