For launching an application, we will need to create an intent that explicitly defines the activity that we wish to start. For example:

Code

        Intent intent = new Intent(this, MyTestActivity.class);

        startActivity(intent);

Intents are created to define an action that we want to perform and the launches the appropriate activity from another application.

Code

        Intent intent = new Intent(Intent.ACTION_SEND);

        intent.putExtra(Intent.EXTRA_EMAIL, recipientArray);

        startActivity(intent);

Each application gets its own Linux user ID and virtual machine which means that the application code runs in isolation from other applications.

Specify android id, layout height and width as depicted in the following example.

<ListView android:id="@+id/ListView01" android:layout_height="wrap_content" android:layout_width="fill_parent"></ListView>

Android Application Architecture has the following components:

> Services - like Network Operation

> Intent - To perform inter-communication between activities or services

> Resource Externalization - such as strings and graphics

> Notification signaling users - light, sound, icon, notification, dialog etc.

> Content Providers - They share data between applications

- AIDL is the abbreviation for Android Interface Definition Language. 

- It handles the interface requirements between a client and a service to communicate at the same level through interprocess communication. 

- The process involves breaking down objects into primitives that are Android understandable.

AIDL supports following data types:

- String

- List

- Map

- CharSequence

- All native Java data types like int,long, char and Boolean

The use of XML-based layouts provides a consistent and somewhat standard means of setting GUI definition format. In common practice, layout details are placed in XML files while other items are placed in source files.

The foreground activity, being the most important among the other states, is only killed or terminated as a last resort, especially if it is already consuming too much memory. When a memory paging state has been reach by a foreground activity, then it is killed so that the user interface can retain its responsiveness to the user.