Question

Describe in detail the process for maintaining a list of items on an activity layout. Discuss each of the components used. Be sure to discuss how data is bound to a list with a custom layout .. Android Studio

Answer 1

Explanation::

An activity is nothng but asingle screen of user interface like a window. While Building an App in Android studio it is one of the crucial component. Activities are launched and they are put together is the fundamental part.

A layout defines the structure for the user interface in the app.

The layout for the list item has been kept in a separate layout file so that the adapter can create view items and can edit their contents independently from the layout of Activity.

In other programming languages the apps are launched using main() method but in android studio initiates the code in Activity instance using various callback methods which are included in lifecycle stages.

Activity serves as an entry point to the application for the user. One activity implements one screen and one activity can loosely coupled with the other activities in an application.

Intent filters provides the ability to launch the activities.

Managing the process or maintaining the items include the activity lifecycle in which activity goes through series of steps:

OnCreate() : when system Creates activity our app should create views and bind data to lists where this method gets in the use.

OnStart() :The activity is visible to the user as soon as OnCreate() exits in this state.

OnResume(): when the activity starts interacting with users this callback occurs.

OnPause(): When the activity is going to loose its focus or loosed its focus then OnPause() callback is called. After this callback eighther the Onstop or onResume gets called.

OnStop(): When the activity is no longer visible to the user then this callback occurs.

OnRestart(): OnRestart() can restores the state of activity in which it was resumed or stopped.

OnDestroy():This system invokes this callback before the activity is destroyed.It ensures that all the resources are released.

The four main components used in application are:

Activities,Services,Broadcast Receivers,Content providers.

Activities handles the UI part which is going to interact with users.

Services mainly handles the background process running in the app.

Broadcast receivers handles the communication between Application and operating system.

content providers deals with database managment issues.

The easiest way to display information to the users can be dne via ListView Component.

Unique set of information in scrollable region can be seen via ListView.

We can create our own data layout using ListViews.

ArrayAdapter are used to manage the data for the ListView. i.e via The adapter is assigned to the ListView via the setAdapter method on the ListView object.

ArrayAdapther class allows removes all lemets in underlying data structure.

The Data Binding Library is a support library that allows us to bind UI components in our layouts to data sources in the app using a declarative format rather than programmatically.

Layouts are often defined in activities with code that calls UI framework methods.

The Data Binding Library automatically generate the class which are going to required to bind the views inside the  layout with data objects. The library provides features :imports, variables, and includes that we can use in our layouts.

While creating and binding custom layout we need to perform the steps:

1. Extend class from viewGroup class.
2. Override OnLayout method
3. Override OnMeasure method(it will be used to determine the size of viewGroup)
4. OnMeasure and OnLayout method will organize child views within parent Layout.

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