Working with Multiple Activities PowerPoint Presentation, PPT - DocSlides

Working with Multiple Activities

Introduction

Working with multiple activities

Creating multiple views

Introduction to intents

Passing data to activities

Putting together the AndroidManifest.xml file

Multiple Activities (Introduction)

When the user switches between activities, one activity is stopped, and the other is started

Remember the activity lifecycle

Note that you can start activities that belong to other applications

A mail program for example

We will not do that

yet

We will work within our own application

Starting an Activity

To start a new activity, you call

startActivity

()

passing an

Intent

as the argument

The

Intent

describes the activity that you want to start

The user can then select from the possible

intents (external)

Or the activity just runs (external)

An activity can also return results

Creating a Second Activity

Remember that an activity is just a class

So we just

add a new class

Inherit from

android.app.Activity

Add the activity to the manifest

Creating aSecond Activity

Add to Manifest

Resulting Manifest

Creating a Layout

You have created portrait and landscape layouts

When working with multiple activities, you need to create layouts for those

activities

In the project Explorer, click

New

,

Other

Creating a Layout (Illustration)

In the first dialog, select Android XML Layout FileIn the second dialog, select the desired layout

Creating a Layout (Illustration)

Set configuration optionsNote the file is added to the res/layout folder by default

Introduction to Intents

Before we can explicitly start an activity, you need to understand intents

An

intent

is an object used to communicate with the OS

Intents are used with activities, services, broadcast receivers, and content providers

We have only discussed activities so far

You can use intents to tell the Android OS which activity to start

Intents (Philosophically)

As the name implies, it’s an intention to do an action

It’s a message to say

I did something

I want something to happen

When you create an intent, you are saying that you want to move from one activity to another

Intents (Types)

There are two types of intents

Explicit

intents

are used with a Context and Class object to start an activity within your application

Implicit

intents

are used to start activities outside of your application

Not

yet

THERE ARE MUCH MORE TO INTENTS THAN DISCUSSED HERE

Intent (Constructor)

This is but one of the many constructorsThe first argument contains the current activityThe second argument contains the class name of the activity to be started

Intent (Creating)

The following appears in the current activity (MainActivity.this) and starts the second activity (Page2Activity.class)

Starting an Activity (Illustration)

startActivity is called with an Intent. The ActivityManager uses that intent to determine the activity to start

Passing Data to Activities

You can pass data from one activity to anther through

intent

extras

Extras are just arbitrary data that can be passed to an intent

An extra is a key / value pair that is passed to an intent

The started activity can read this extra data

Creating (Writing) an Extra

First,

create the

Intent

as shown before

Second, call

putExtra

()

First argument contains the key

Second argument contains the value

Creating (Writing) an Extra

The first argument contains the key, which here is a constant “LastActivity”The second contains the value “MainActivity”

Reading an Extra

The

getIntent

()

method returns an

Intent

object

It’s methods get values of a particular type

getBooleanExtra

()

,

getByteExtra

()

,

getIntExtra

()

, etc…

Reading an Extra (Example)

Read an extra into a TextView

Returning an Activity Result (Introduction)

There are times when we need to return a result from an activity

We start an activity as before, however, pass a request code when starting the activity

The request code is an integer

It is send to the child (started) activity

The result is then returned to the parent

Returning an Activity Result

Call

startActivityForResult

()

instead of

startActivity

()

The first argument contains the intent

The second argument contains the integer result that will be returned

The result is returned

through overriding

onActivityResult

()

in the parent activity

Returning an Activity Result

To return the result, you call one of two forms of

setResult

()

The first returns a result code

Typically

Activity.RESULT_CANCELED

Activity.RESULT_OK

The second return the result code and intent

data

Call

finish()

to return from the activity

Activity Result Example (1)

Start the activity as before with startActivity except call startActivityForResultThe first argument contains the activity as beforeThe second argument contains an integer request codeIt answers the question, from which activity are we returning

Activity Result Example (2)

Here we return a code but no dataThe intent is empty and has no extrasRESULT_CANCELED is an android constantWe call finish to return to the calling Activity

Activity Result Example (2a)

Here we return a code and dataThe Intent has extra dataWe change the return code

Activity Result Example (3)

In the calling activity, handle the

onActivityResult

()

event

AndroidManifest.xml (Multiple Activities)

The AndroidManifest.xml must list all of the activities

Remember one activity is designated as the launcher activity

AndroidManifest.xml(Multiple Activities)