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Notes on video lecture:
The Activity Class
Notes taken by Edward Tanguay on June 23, 2014 (go to class or lectures)
Choose from these words to fill the blanks below:
restarted, memory, saved, backstack, kill, recalculate, interacting, user, cache, onPause, class, code, user, availability, layout, closed, methods, terminates, element, application, lifecycle, object, functionality, XML, suspended
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resources
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layout files
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specifies what some part of your                        will look like
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these are        files
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in res/layout/*.xml
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access them in Java as R.layout.layout_name
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access them by other resources as @layout/layout_name
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you can have multiple              files which android can choose from at runtime based on your configuration
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e.g. main.xml
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RelativeLayout
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EditText
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Button
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layout-land
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if held horizontal, then this layout file will be used
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Android generates a            called R from the application
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the layout class with main field gives you a handle to the main.xml file
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implement classes
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involves writing at least one activity
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in onCreate() you do four things:
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1. restore saved state
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2. set content view
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3. initialize UI elements
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4. attach          to those UI elements
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e.g. MapLocation application
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MapLocation extends Activity
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protected void onCreate(Bundle savedInstanceState)
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a data structure containing anything Android might have            the last time
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onCreate has to call super.onCreate
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setContentView(R.layout.main)
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for the UI elements, you pass in the id of the desired               
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setOnClickListener(...) defines what happens when user clicks
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package application (.apk file)
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AndroidManifest.xml
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name of application
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list of components
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other information
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permissions
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hardware features required (e.g. camera)
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minimal application
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minimum API level
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install and run
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you can do this in eclipse or from the command line using the adb tool, e.g.
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adb install PATH_TO_APK
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activity class
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primary class for interacting with users
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provide a visual interface
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by convention, activities should be modular
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a single, focused thing
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viewing e-mail
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logging in
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you then string together tasks
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task backstack
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tasks need to be properly                    and resumed
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a task is a set of related activities
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can span multiple applications
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when user hits home button, the current task is temporarily             
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when activity is launched, it's pushed onto the task                   
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when it is destroyed:
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user hit back button
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program terminated itself
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android decided to kill that activity in order to reap its resources
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when task1 e.g. has a button to got to task2, its state is captured so user can go back to it
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when back button is clicked, activity is killed, and next activity in task backstack is started
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the activity lifecycle
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acvitities have a                    but are not in control of it
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depend on user behavior
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android can          activities
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lifestyle states
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resumed/running state
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activity is visible and          can interact with it
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paused
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visible
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user not                        with it
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can be terminated
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stopped
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no longer visible
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android may terminated it
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activities need to behave differently during different states of lifecycle
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Android announces lifecycle changes by calling template               
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onCreate
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onStart
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onResume
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onPause
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onRestart
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onStop
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onDestroy
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you can override any of these in order to hook in                            for each state
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simple application: one activity, starts, waits, closes
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the visible lifetime is between onStart() and onStop()
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the interactive lifetime is between onResume() and onPause()
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e.g. if the phone goes to sleep, then onResume() is called
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if e.g. in the map application map covers the whole activity, then onStop() is called since the activity is no longer visible
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then when back button clicked: onResume(), onStart()
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onStop() may be skipped if Android                      the application
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onCreate()
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four functions
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super.onCreate()
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sets activity's content view
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retain reference to UI views
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configure views
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onRestart()
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to handle special processing
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e.g. if you have to check the database again or some API call
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onStart()
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activity is about to become visible
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loading persistent application state
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onResume()
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activity is visible and about to start interacting with the         
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starting animations
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playing background soundtrack
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onPause()
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shut down foreground-only behaviors
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save persistent state
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onStop()
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may be restarted later so:
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cache actvitity state
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remember: may not be called when activity terminates, e.g. if Android kills it due to low             
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therefore, save activity state in                since that is always called before activity is terminated
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onDestroy()
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release activity resources
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shutting down private threads started by this activity
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may not be called, e.g. if activity is killed
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starting activities programmatically
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create intent
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pass it to startAcvitity()
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pass it to startAcvitityForResult()
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assumes a result come back
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Activity.setResult()
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passing in a result code and data
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and a resultCode:
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RESULT_CANCELED
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RESULT_OK
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RESULT_FIRST_USER
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confiuration changes
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languages use, screen size, device                         
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when these change, Android will usually kill running activities and restart them with the changed configuration
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e.g. from portrait mode to landscape mode and back
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the activity will be killed and                    twice
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so if your startup code is slow, it will affect the user experience
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to speed this up, you can save and            important state information
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cache hard to                        data by calling onReatinNonConfigurationInstance()
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called between onStop() and onDestroy()
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then in onCreate(), call getLastNonConfigurationInstance()
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or you can manually handle it, define this in the AndroidManifest.xml
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then the activity's onConfigurationChanged() method gets an              specifying the new configuration, e.g. if from landscape to portrait
Android Architecture
The Android Development Environment
Developing an Android App
The Activity Class
Fields of the Intent Class
Android Permissions
The Fragment Class