Overview of Android Intents (Part 1)

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From the course by Vanderbilt University

Android App Components - Intents, Activities, and Broadcast Receivers

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Vanderbilt University

Android App Components - Intents, Activities, and Broadcast Receivers

293 ratings

Course 2 of 5 in the Specialization Android App Development

This 4 week MOOC builds upon the overview of Java and Android covered in Course 1 by delving deeper into core Android app components, such as intents, activities, and broadcast receivers. You will learn by example how to program these core Android components together with Android concurrency frameworks and basic Java file I/O classes (such as File and InputStream) and Android storage mechanisms (such as Shared Preferences). You'll also learn how to use the Git source code management system. Throughout this MOOC you'll work incrementally on a project involving downloading, storing, and display images from remote websites. Each week you will add additional capabilities to the project, based on material covered in the lecture videos. You'll spend roughly 4 hours per week watching video lectures, taking quizzes, and programming assignments with Java and Android.

From the lesson

Android Intents

This module describes the structure, functionality, and use of Android intents that provide an abstract description of an operation to perform or an event that has occurred.. Android uses intents as the "glue" that simplifies the integration of apps that reuse existing components, such as activities, services, and broadcast receivers.

Overview of Android Intents (Part 1)7:53

Overview of Android Intents (Part 2)7:06

Meet the Instructors

Dr. Douglas C. Schmidt
Professor of Computer Science and Associate Chair of the Computer Science and Engineering Program
Electrical Engineering and Computer Science
Michael Walker
Instructor - Graduate Student pursuing PhD in Computer Science
EECS
Dr. Jules White
Associate Professor of Computer Science
Electrical Engineering and Computer Science

[MUSIC]

Welcome to the first part of the first lesson in our module on Android intents.

This lesson provides an overview of Android intents.

Which are a key part of the overall Android component framework.

There's several learning objectives in this part of the lesson.

By the time you complete this part of the lesson

you'll know how intents allow the integration of apps that interact with or

request functionality from other components.

And you also recognize methods used to launch Android components via intents.

This part of the lesson just focuses on concept's, rather than on code.

We'll show plenty of code examples later in this module.

Let's start by talking about how Android intents can be used to integrate

components An intent is a message that one component uses to

interact with or request functionality from other components.

For example, this diagram illustrates three Apps: App1,

App2, App3 and a number of components in those Apps.

In app one,

activity one request functionality from activity two using an intent.

LIkewise, activity two and

app one uses an intent to interact with a receiver component in app three.

More over Activity1 and App1 uses and

intent to start a service it interacts with in App2.

Intents are essentially the glue that helps to integrate Android apps.

App development is therefore simplified

since existing components can e reused as black boxes.

A black box is a component that

only needs to be understood by its interface and not by its implementation.

Let's take a look at a simple example.

Consider an image download app that downloads an image

from a remote web server and displays it to the user.

We'll examine several variations of this app throughout the course.

One way to build this app, of course,

would be to write this whole thing from scratch.

But that would become tedious and error prone very quickly.

So instead what we're going to do is,

we're going to write a main activity component that uses intents

to obtain functionality from other components that already exist.

For instance, we may already have written a DownloadService

component that downloads an image from a remote website and

stores it locally on the device and then returns a URI or

path name to that image, back to the main activity.

The main activity then takes that URI and passes it to the GalleryActivity

component which is pre developed, it comes part of the Android release itself.

And this GalleryActivity then goes around and

displays the image via the Gallery app.

The ImageDownloadApp is simplified since it integrates other existing components,

such as DownloadService and the GalleryActivity,

rather than having the application developer of the ImageDownloadApp write

everything from scratch.

Let's now talk a bit about the structure and functionality of intents.

An intent is implemented as a so-called passive data structure.

A passive data structure just consists of fields and field accessor and

mutator methods.

A passive data structure is sometimes referred to as a record or a pod,

plain old data and it's not object oriented in the sense that it doesn't

necessarily have virtual methods, dynamic binding, it may not use inheritance.

It's really used to be passed around as a record or a set of fields.

The next lesson will examine these fields and methods in greater detail.

The data in the fields in an intent can be passed from one component to another.

This approach is similar to communicating between objects

by passing arguments to a method call.

Android automatically handles the cases where components

live in different processes.

For example, here we see activity one in process1 passing an intent

to service one in process2.

Apps can use intents to describe two types of things.

The first thing they can do is to find an operation to perform.

For example, the ACTION_VIEW intent can be used to display data to the user.

Likewise, the ACTION_CALL intent can be used to perform a call to someone

specified by the data, such as a phone number.

Android delivers the intent to the Activity or

Service that can best handle it that's what we'll discuss later.

And intent can also be used to describe an event that's already occurred.

For example the action battery low intent indicates there's

a low battery condition on an Android device.

Likewise the ACTION_AIRPLANE_MODE_CHANGED intent

Indicates the user has switched the phone into or out of airplane mode.

Once again, Android delivers the intent to the broadcast receiver or

receivers that can best handle it.

Let's now discuss methods that are used to launch components via intents.

A component invokes a method to send an intent to 0 or more components.

And of course, these methods are provided by Android.

The startActivity() and startActivityForResult () methods can be

used to launch an activity With an action intent.

There may be more than one activity that matches an intent so the Android

underlying framework provides something called a chooser dialogue that allows

the user to decide which activity they actually want to have to handle the event.

Sendbroadcast() and various methods related to send broadcast

are used to send event intents to a BroadcastReceiver.

There can be 0 or more of these receivers depending on various conditions,

which we'll discuss when we talk about intent filtering and intent resolution.

And finally is a pair of methods, startService or bindService.

It can be used to launch and communicate with a service via an intent.

Unlike activities or

receivers where there may be multiple potential recipients of the intent,

an intent can only be sent to one service, which we'll discuss later as well.

All the methods we discussed here pass the intents asynchronously.

In other words, they don't block the caller while the various

components carry out the operations in processing related to the intent.

This is the End of the Overview of Android Intents Part 1.

[MUSIC]

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