Working with Multiple Activities

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Introduction Working with multiple activities Creating multiple views Introduction to intents Passing data to activities Putting together the

AndroidManifest.xml file

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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

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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

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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

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Creating aSecond Activity

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Add to Manifest

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Resulting Manifest

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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

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Creating a Layout (Illustration) In the first dialog, select Android XML

Layout File In the second dialog, select the desired

layout

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Creating a Layout (Illustration) Set configuration options Note the file is added to the res/layout

folder by default

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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

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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

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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

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Intent (Constructor) This is but one of the many constructors

The first argument contains the current activity

The second argument contains the class name of the activity to be started

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Intent (Creating) The following appears in the current

activity (MainActivity.this) and starts the second activity (Page2Activity.class)

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Starting an Activity (Illustration)

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

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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

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Creating (Writing) an Extra First, create the Intent as shown before Second, call putExtra()

First argument contains the key Second argument contains the value

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Creating (Writing) an Extra The first argument contains the key,

which here is a constant “LastActivity” The second contains the value

“MainActivity”

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Reading an Extra The getIntent() method returns an Intent object

It’s methods get values of a particular type getBooleanExtra(), getByteExtra(), getIntExtra(), etc…

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Reading an Extra (Example) Read an extra into a TextView

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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

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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

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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

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Activity Result Example (1) Start the activity as before with startActivity except call startActivityForResult The first argument contains the activity as

before The second argument contains an integer

request code It answers the question, from which activity

are we returning

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Activity Result Example (2) Here we return a code but no data

The intent is empty and has no extras RESULT_CANCELED is an android constant We call finish to return to the calling

Activity

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Activity Result Example (2a) Here we return a code and data

The Intent has extra data We change the return code

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Activity Result Example (3) In the calling activity, handle the onActivityResult() event

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AndroidManifest.xml (Multiple Activities) The AndroidManifest.xml must list all of

the activities Remember one activity is designated as

the launcher activity

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AndroidManifest.xml(Multiple Activities)