Mobile System Midterms

Activity

This represent a single screen in the app where the user can perform a single focused task such as sending an e-mail. It is usually presented to the user as a full-screen window.

To implement an activity

1. Create an Activity Java class.

2. Implement a basic UI for the Activity in an associated XML layout file.

3. Declare the new Activity in AndroidManifest.xml.

Activity Life Cycle

This is the set of states an activity can be in during

its entire lifetime.

onCreate()

It is invoked when the app is launched for the

first time. It happens only once for the entire

life of the activity.

onStart()

It is invoked before the activity becomes

visible to the user.

onResume()

It is invoked before the activity starts interacting with the user.

onPause()

It is invoked when the system is about to start resuming another activity.

onStop()

It is invoked when the activity is no longer visible to the user.

onDestroy()

t is invoked when:

• the activity is finishing (due to the completely dismissing the activity or due to finish() being called on the activity)

  • the system is temporarily destroying the activity due to a configuration change (such as device rotation or multi-window mode)

onRestart()

It is invoked if the activity comes back after being stopped. It is always followed by onStart().

Back Stack

Each time a new activity starts, the previous activity is stopped, but the system preserves the activity in a stack called “____“

Intent

It is an asynchronous message that is used in an activity to request an action from another activity, or from some other app component.

Parts of an intent

• Target Activity

• Intent data/object

• Intent extras

• Intent flags

Types of intent

• Explicit Intent

• Implicit Intent

Target Activity

The activity that will receive the intent.

Intent data/object

This contains a reference to the data you want the receiving activity to operate on.

Intent Extras

This carry information the receiving activity requires to accomplish the requested action (optional).

Intent flags

This may instruct the Android system how to launch an Activity or how to treat it after it’s launched (optional).

Explicit Intent

The target of the intent (the class name of the activity) is already identified.

Implicit Intent

The target of the intent is not yet identified but there is a general action to perform. It also includes an action, category, and data type.

parentActivityName

This attribute indicates that the main activity is the parent of the second activity.

Layout

This define the structure for an app’s user interface.

View

This draws something the user can see and interact with.

ViewGroup

An invisible container that defines the layout structure for View and other ViewGroup objects.

Declare UI elements in XML

The presentation of the app can be separated from the code that controls its behavior.

Instantiate layout elements at runtime

The View and Viewgroup objects can be created and their properties can be manipulated programmatically.

Context

This is an interface to global information about an application environment.

wrap_content

This sets the size of the view to dimensions required by its content.

match_parent

This sets the view to be as big as its parent view group will allow.

Constraint Layout

This creates large and complex layouts with a flat view hierarchy (no nested view groups).

Linear Layout

This organizes its child view elements into a single horizontal or vertical row.

Relative Layout

This is used to specify the location of child objects relative to each other (child A to the left of child B) or to the parent (aligned to the top of the parent).

Web View

This is used for displaying web pages.

Frame Layout

This is designed to block out an area on the screen to display a single item.

Table Layout

This arranges its child objects into rows and columns.

Grid Layout

This arranges its child objects in a rectangular grid that can be scrolled.

Notification

This is a message that Android displays outside the app’s UI to provide the user with reminders, communication from other people, or other timely information from the app.

Notification Drawer

This allows to view more details and take actions with the notification.

App bar/action bar

This provides a visual structure and interactive elements that are familiar to users.

Toast

This provides simple feedback about an operation in a small popup.

Snackbar

This provides a quick pop-up message to the user.

Dialog

It is a small window that prompts the user to make a decision or enter additional information. It is not designed to fill the screen.

Menu

It is used to present user actions and other options in the app’s activities.