Busy Android Developer's GuideBusy Android Developer's Guideto UI

Ted NewardNeward & Associates

http://www.tedneward.com | ted@tedneward.com

CredentialsCredentials

Who is this guy?– Architectural Consultant, Neudesic Software– Principal, Architect, Consultant and Mentor

ask me how I can help your project or your team– Microsoft MVP (F#, C#, Architect)– JSR 175, 277 Expert Group Member– Author

Professional F# 2.0 (w/Erickson, et al; Wrox, 2010)Effective Enterprise Java (Addison-Wesley, 2004)C# In a Nutshell (w/Drayton, et all; OReilly, 2003)SSCLI Essentials (w/Stutz, et al; OReilly, 2003)Server-Based Java Programming (Manning, 2000)

– Blog: http://blogs.tedneward.com– Papers: http://www.tedneward.com/writings– Twitter: @tedneward

ObjectivesObjectives

Our goal here today is...– ... to get familiar with the various Android UI elements– ... to come to understand XML layouts– ... to learn how to handle events within Android UIs

Activities and TasksActivities and Tasks

Activity– somewhat akin to a web page or screen– public class that extends android.app.Activity– activities have event methods for override

onCreate: activity "constructor"onDestroy: activity "finalizer"onStart/onResume/onPause/onStop/onRestart flowremember to always call up the inheritance chain

Activities and TasksActivities and Tasks

Tasks– Tasks are the logical thread of use through Activities

usually starting from the Home screen– Tasks form a "back stack" of Activity instances

"back" button removes the top card, destroys that activity– Tasks are distinct from one another

•a new task creates a new stack of cards•this means more than one Activity instance of the same type is possible

– Tasks cross applications and processesin this respect, Activities are like web pages

ViewablesViewables

View and ViewGroups– View is the base class for "widgets"– ViewGroup is the base for Composite-patterned containers

of other View objects (including other ViewGroup instances)

– Each Activity can hold one content Viewmost often, this is a ViewGroup, forming a hierarchy

– Custom Views and ViewGroupsyou can do them, but it's pretty rare

ViewablesViewables

Widgets (android.widget)– "Push Me": Button, CompoundButton, CheckBox,

ImageButton, RadioButton– Text: EditText, TextView, NumberPicker, TextSwitcher– Graphics: Gallery, ImageSwitcher, ImageView– Selectors: RatingBar, SeekBar, Spinner, Switch– Time: AnalogClock, DigitalClock, Chronometer,

CalendarView, DatePicker, TimePicker– Composite: ListView, SlidingDrawer, TabHost– Media: MediaController– Space (literally, just that--empty space!)– ... and a few more

ViewablesViewables

Layouts (android.widget)– LinearLayout– RelativeLayout– TableLayout– GridLayout– AbsoluteLayout (bad!)– FrameLayout (mostly useless!)

ViewablesViewables

Dialogs (android.app) are a special case of Activity– AlertDialog (OK/Cancel/Help, etc)– ProgressDialog (56 of 100...)– DatePickerDialog– TimePickerDialog

But Dialogs are not Activities– Dialogs are always created and displayed as part of (and

are "owned" by) an Activity; as such, they are intimately wrapped up in their host Activity's code

– AlertDialog is the workhorse here

CreationCreation

Two ways of creating UIs in Android– either create UI "by hand" in Java– or using XML-based layout (resource) file

•layout resources are not tied to an Activity; they are just a group of Views laid out in an XML file•layout resources can be "inflated" from XML into UI objects (via a system service)•Activity.setContentView() is a shortcut way to do this

Layout ResourcesLayout Resources

Layout resources are in res/layout directory– XML file name corresponds to R.layout.{filename}– Root element is (usually) a ViewGroup (Layout class)– android: namespace is mandatory– element attributes describe "setter" values– android:id is critical for manipulation

•"@+{prefix}/{name}" defines new R.{prefix}.{name} id•{prefix} is most often "id" but isn't required•IDs don't have to be unique across the entire tree (but usually are)

Layout ResourcesLayout Resources

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <ListView android:id="@+my_team_ids/lstInvitees" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="6dip" /> <LinearLayout android:orientation="horizontal" android:layout_width="fill_parent" android:layout_height="fill_parent" android:gravity="bottom"> <TextView android:text="Add:" android:layout_width="wrap_content" android:layout_height="wrap_content" /> <EditText android:id="@+my_team_ids/txtNewTeamMember" android:layout_width="wrap_content" android:layout_height="wrap_content" android:hint="(Email address)" android:maxLines="1" /> <ImageButton android:id="@+my_team_ids/btnInvite" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@android:drawable/sym_action_chat" /> </LinearLayout></LinearLayout>

Layout ResourcesLayout Resources

Layout resources can be "tuned"– like all resources, layouts can be spceialized to particular

scenarios•screen size: "small", "normal", "large", "xlarge"•orientation: "port", "land"•pixel density: "ldpi", "mdpi", "hdpi", "xhdpi", "nodpi", "tvdpi"•platform version: "v3", "v4", "v7", ...

– this is one way to customize UI to different device profiles•the above qualifiers MUST be in that order•see ${SDK}/docs/guide/topics/resources/providing-resources.html

MenusMenus

Menus– Activities can also have menubar items associated with

thembest used for actions that aren't common or frequent

– Menus are often defined in layout (res/menu)menu: define a menu, a container for menu itemsitem: define a menuitem, with id, icon and title (text)group: convenience grouping of item elements (invisible)

MenusMenus

<menu xmlns:android="http://schemas.android.com/apk/res/android"> <item android:id="@+id/new_game" android:icon="@drawable/ic_new_game" android:title="@string/new_game" /> <item android:id="@+id/help" android:icon="@drawable/ic_help" android:title="@string/help" /></menu>

MenusMenus

ActionBar (3.0+)– A set of menus/menuitems appearing at the top

generally only useful for tablets

Event-handlingEvent-handling

Most Views/ViewGroups offer events for code to subscribe to– These are called "InputEvents"– Most of the time, this is the classic "Listener" idiom

View.OnClickListeners can be wired up in the XML layout– Most of the time, these are wired up in onCreate()

IntentsIntents

Moving from one Activity to another requires an Intent– Intent = Action (verb) + Context (target)– easiest Intent is the "launch the Activity" Intent

Intent next = new Intent(this, NextActivity.class);startActivity(next);

ThreadingThreading

Good Thread hygiene is critical here– This is a phone--you don't own the machine!– Android isn't quite like Java, and has a slightly different

"take" on the threads-and-UI positionno blocking behaviors (in general)NO UI modifications from non-UI threadIf the UI thread is inactive for more than 5 seconds, bye!

– Android provides Handlers, which can be sent Messages that will then be processed on the Activity's UI thread

– Java5 provides a few other constructs as well

Wrapping upWrapping up

"What do you know?"

SummarySummary

Android is a Java-based mobile device framework... but it's not Java... and it's not a web app technology... and it's definitely not Swing or SWT

ResourcesResources

Busy Coder’s Guide to AndroidMark Murphy, http://www.commonsware.com

Android websitehttp://developer.android.com

Presentations by this guy– Busy Android Dev's Guide to Persistence– Busy Android Dev's Guide to Communication– ... and more