hit3328 - chapter04 - complex interactions

HIT3328 / HIT8328 Software Development for Mobile DevicesDr. Rajesh Vasa, 2011

Twitter: @rvasa Blog: http://rvasa.blogspot.com

1

Lecture 04Complex

Interactions

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Lecture Overview

•Recap (previous 2 weeks)

• Passing Data between Activities

• Data passing methods

• Activity Design Choice

• Activity Life Cycle

• Passing Data Demo (using Global Variables)

•Application Manifest File

• Passing Data Demo (using Intents)

•Controlling Input Type

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Android Device User Interaction

Menu

HomeBack

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Android App. is made of Activities

Activity

View Group

Views(Layout)

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User Interface (generally) Built in XMLActivity

View Group(Layout)

Activity Class (Java)

Layout Definition (main.xml)

PresentatioPresentationn

FunctionaliFunctionalityty

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The Android Way - Convention not Config.

•Source code (src)

•Generated code (gen)

•Resources (res)

•Images (@drawable)

•Layout of app (layout)

•Constants/Strings (@strings)

Conventions to Follow

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Portrait and Landscape Layouts


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Provide Resources @Multiple Resolutions

High

Low

Medium


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View Identifiers

@+id TAG creates new identifiers


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UI Interaction Handling Pattern

•Component.setOn......Listener ( handler )

• E.g. button.setOnClickListener

•Handler is an anonymous inner class

• On...Listener handler = new On....Listener() {}

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Android Activity Life Cycle

onCreate is called when Activity Starts

Activity is re-started

when orientatio

n changes

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We Retrieve State On Creation

State retrieval done here

onSaveInstanceState() is called from this

state(Save Saved here)

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Bundle stores simple state information

BundleBundle

putString(key, value)

putDouble(key, value)

putInt(key, value)

putStringArray(key, value[])

It is a Key, Value store system(like a Hash Table or a Hash Map)

Code Snippet:

state.putString("inputTemperature", inputTemp);

Code Snippet:

state.putString("inputTemperature", inputTemp);

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Working with Resources

off.png

Layout XML File

Via Java Code

on.png

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Short Problem 1 - Passing Data

•Context: In Android -- Apps are made of Activities. So, each Screen is a “new” Activity

• We want to pass data between Activities.

• But, Activity construction is managed by the Dalvik runtime. That is, cannot pass data into constructor.

•What would you prefer to do?

• Store shared data in global variables available to ALL Activities.

• Move all data to a separate data layer.

• Send primitive data bundles between activities/screens.

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Lecture Overview


•Passing Data between Activities







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Wiring up Activities -- Typical Use Case

Select

Back

Contact List Activity Contact Details

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Wiring up Activities -- Typical Use Case

Select

Contact List Activity Contact Details

We re-use this activity with

different data

Select

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Lecture Overview



• Data passing options





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Data Passing Option - Global Variables

•We can use Global Variables ... but,

• Widely accepted as a “risky” choice

• A few global variables are used in many large systems (e.g. Linux Kernel Source Code)

• Risk manageable in ‘small’ programs

• Good thread @ StackOverflow http://goo.gl/EouH3

•Constant values as globals is ok (e.g. R.java)

•Key Issue (to manage): How many objects are able to change the value of a global variable

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Data Passing Option - Data Layer•We can store all data in a DBMS and access

it via a “data layer”

• Good idea when dealing with large / complex blocks of data

• Overkill if we only need to store a few values

•The data store can be “in-memory”, “on-disk”, and/or “on remote server”

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Data Passing Option - Bundles

•We can put data into a bundle and pass this across using a “messaging framework”

• Simple (once you understand the messaging framework architecture)

• Persistence is not managed (like DBMS)

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Data Passing Option - iOS Only!!•You can pass data directly to methods in

another screen (UIViewController)

• UIViewController is approx. similar to Activity

•This option is not possible in Android -- this was a “design intent” (design side-effect?)

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Lecture Overview









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iOS Apps. are directly managed by O/S

UIAppDelegateUIAppDelegate

UIViewController-UIViewController-AA

UIViewController-UIViewController-BB

UIViewController-UIViewController-CC

UIAppDelegate has Life Cycle View Controllers are

managed by the App internally

Image Source: Apple Inc.

Life Cycle => Managed by Operating System

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Android Activities are Managed by O/S

Activity-AActivity-A

Activity-CActivity-C

Activity-BActivity-B

ApplicatiApplicationon Activities have

a parent application

Activity has Life Cycle Application is NOT managed directly by

the O/SLife Cycle => Managed by Operating System

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A Key Design Different (iOS Vs Android)




UIAppDelegateUIAppDelegate

UIViewController-UIViewController-AA

UIViewController-UIViewController-BB

UIViewController-UIViewController-CC

ApplicatiApplicationon

UIAppDelegate has Life Cycle

Activities have a parent

application

Activity has Life Cycle Application is NOT managed directly by

the O/SLife Cycle => Managed by Operating System

View Controllers are managed by the App

internally

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Activity Life Cycle Design Choice....•Android developers decided to give Activity

a life cycle (rather than the application)

•This makes each Activity similar to a separate program

•Hence, data passing is restricted to:

• Global Variables (stored in Application object)

• Data bundles passed via async. messages

• Data stored externally in files or DBMS

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Short Problem 2 - Activity Design Choice

•Unlike iOS ViewControllers, Activities have been modelled to be (almost) like independent programs

• What is the likely rationale for such a choice?

• What would be the benefits?

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Only One Activity is Active/Running•Only one Activity can

be in the ‘foreground’

•When Activity-A calls Activity-B

• Activity-B will be visible to the user (foreground)

• Activity-A is paused (background)

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Activities are Stacked in Android•All created activities are placed on a Stack

•Activities ‘popped’ when ‘Back Button’ is pressed


Foreground/Active

If only one activity is on the Activity

Stack then “back” button exits it

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Activities are Stacked in Android•All current activities are placed on a Stack

•Newly started activities come into foreground



Foreground/Active

startsBackground/

Paused

Back button will pop top most activity from

stack

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Activities are Stacked in Android•As additional activities are started, older

activities go into background

•All activities are placed on Activity Stack



Activity-CActivity-CForeground/Active

starts

starts

Background/Paused

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Short Problem 3 - Activity Stacking•Consider the following situation,




starts

starts


starts

Are these activities the same object?

Ponder the interaction design implications .....

Will Back Button Exit the App?

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Lets get our feet wet

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Lecture Overview









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Demo 1 - Life Cycle of an Android App.

•Walk-through of code provided along with lecture handout.

• We can see the states by adding a little bit of logging code to a few call-backs

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Life-Cycle Demo

onCreate, onStart, onResume etc. are from the

Activity class

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Life-Cycle Demo (Watching State)

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Lecture Overview






• Passing Data Demo (Global Variables)




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Demo 2 - Passing Data

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Before data passing -- a quick recap•This app. makes use of nested layouts

•We can also make it look a bit nicer using weights

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Anatomy of the App. (Nested Layout)

Linear LayoutTextViewImageViewLinear Layout

Button (Fruit)Button (Vegetable)Button (Drink)

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A Weighty Problem

Spot the difference in layout

How achieved? android:layout_weight=”1”for all buttons in the layout

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Layout Weights are Handy

If all buttons are given the same weight, then they will

be of same size

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Demo 2 - Passing DataActivity - FoodMain Activity - FoodView

Data Passed:Name (“Fruit”)

Image (fruit.png)

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Passing Data with Globals

•All Activities have a parent Application object

•We can store data in this Application object




ApplicatiApplicationon Activities have

a parent application

We need to extend the

Application class to do this

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What Creates/Manages Application?•Application is created and managed by the

Android runtime

•There is one Application object created by default

•We can extend the “Application Class” and make our own

•But, we need to tell the Runtime about this Application object via the Manifest XML file

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Lecture Overview










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Manifest contains Application Metadata• Android runtime creates the Application object

• Application metadata is provided in the Manifest XML

Manifest XML file is part of the project

Auto-generated by Eclipse IDE

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Manifest XML - What is it?

Manifest informs Runtime about the App.Manifest informs Runtime about the App.

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Manifest XML - Contents

Application Name

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Manifest XML - Contains Activity Names

Activity Name(s)

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Manifest XML - Refers to Icons

Launcher Icon

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Manifest XML - Refers to the App. Name

Application Label

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Passing Data with Globals

•All Activities have a parent Application object

•We can store data in this Application object

FoodApplicatiFoodApplicationon


We need to extend the

Application class to do this

extends

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Global Vars. can be in the Application

FoodApplicatiFoodApplicationon


extends

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Activities and Globals in Application•Activities can access data from the

Application object

We can also get to these variables from any Activity(declared in the Manifest XML file)

We can also get to these variables from any Activity(declared in the Manifest XML file)

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Lecture Overview









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Demo 2 - Passing Data using IntentsActivity - FoodMain Activity - FoodView

Data Passed:Name (“Fruit”)

Image (fruit.png)

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Wiring up the Buttons (Another Way)

Buttons support onClick

in the layout XML

Buttons support onClick

in the layout XML

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Storing Data in a Bundle

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Sending an Async. Message

Android uses an asynchronous messaging model (known as Intents) to send messages

between Activities

Android uses an asynchronous messaging model (known as Intents) to send messages

between Activities

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Setup Message and Store Data in the Message

Setup Message and Store Data in the Message

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Class that is sending the Intent (message)Class that is sending the Intent (message)

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Class that will receive the Intent (message)

Class that will receive the Intent (message)

Class that is sending the Intent (message)Class that is sending the Intent (message)

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Send the Message to the Activity (Transmit)

Send the Message to the Activity (Transmit)

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Message Receiving

Retrieve data from the message

Retrieve data from the message

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Intent Messages are Asynchronous•The intent system is completely

asynchronous -- similar to e-mail

•That is,

• The receiver will get the message only if they request to see intents via getIntent() method

•All transmitted messages are placed on a ‘Service Queue’

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Complex Domain Models

•Where do you hold a complex domain model?(E.g. we have 4-5 classes in a domain model)

• We can hold a reference to the domain model objects in the Application

•This is fine if there are only a few objects

•Unlike Activity, Application is only terminated if device runs low on memory

• If the data size is larger -- then best to use the sqlite database

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Lecture Overview









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Controlling Input Data Type

•A common task on forms is to restrict users to certain data types

• Email Address

• Decimal Numbers

• Positive Integers

• Alpha Numeric

•On mobile devices -- development platforms offer a simple way to control the keyboard type

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Controlling Input Type (Android)•Android has a large number of options

•You can merge them to create more complex input types

textUritextEmailAddresstextPasswordtextPersonNamenumbernumberSignednumberDecimalnumberPassword

textUritextEmailAddresstextPasswordtextPersonNamenumbernumberSignednumberDecimalnumberPassword

android:inputTypeandroid:inputType

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Input Type - Example

http://developer.android.com/reference/android/widget/TextView.html#attr_android:inputType

More info. at the following URL

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Lecture Recap









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What’s next?

•Usability Principles - Mobile Form Design

•Using Dialogs

•Returning data back from an Activity

•Simple File I/O

•More complex layouts

•Exploring a few more widgets

hit3328 - chapter04 - complex interactions

Design

weekspassing data

shared data

data intoconstructor

rajesh vasa

valuesthe data store

data layergood idea

separate data layer

primitive data bundles