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

- Notification messages to the user from an Android enabled device can be displayed using Intents.

- There are two types of Intents - Explicit Intent, Implicit Intent.

Implicit Intent:

- In case of Implicit Intent, an intent is just declared. 

- It is for the platform to find an activity that can respond to it.

- Since the target component is not declared, it is used for activating components of other applications.

Explicit Intent

- Explicit intent specifies the particular activity that should respond to the intent. 

- They are used for application internal messages.

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.

A call to onStop method happens when an activity is no longer visible to the user, either because another activity has taken over or if in front of that activity.

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.

Yes, it is possible to do that, such as when you want to create a background behavior for a particular activity. You can do this by using add(Fragment,string) method to add a fragment from the activity.