CE881: Mobile & Social Application Programming

Transcription

1 CE881: Mobile & Social Application Programming Fragments and Jialin Liu Senior Research Officer Univerisity of Essex 13 Feb 2017

2 Today s App : Pocket (1/3)

3 Today s App : Pocket (2/3)

4 Today s App : Pocket (3/3) ideashower.readitlater.pro&hl=fr

5 Fragment Fragments Fragments offer a powerful way to compose Apps in a highly modular way Choice of Layout can easily depend on screen size Each Fragment has it s own lifecycle, tied to its parent activity s cycle Composing an Activity from several fragments offers flexibility The overhead is additional coding

6 Fragments and Android API Versions Fragments always belong to an Activity i.e. an Activity hosts a Fragment Fragments have native support from API 11 (Honeycomb, 3.0) onwards, any Activity can host a Fragment With earlier APIs and the Support Library, a FragmentActivity is needed (or a sub-class of this) This also leads to some differences in the code

7 Example Fragments Question : in each case how would you achieve the above without using Fragments??See fragments/fragment-ui.html for examples

8 Defining Fragment GUIs Fragments Like other layouts, can be done in XML or in Java code XML trick : Define two layouts, one for small screen, one for tablet (large screen) The one for the tablet must be in a directory with the large qualifier e.g. two layouts could be : res/layout/news_articles.xml res/layout-large/news_articles.xml When the layout is inflated the correct one will be chosen Following shows FragmentBasics example on Nexus One and Nexus 7 emulators

9 FragmentBasics Example Note the different layouts Fragments

10 in Java Code Fragments When Fragments are added to XML layouts they cannot be removed in code Alternative : Fragments can be added or removed with the appropriate Java This enables dynamic construction of GUIs BUT NOTE : all additions and removals of Fragments MUST be done within a Fragment Transaction Question : why is this so?

11 Implementing Fragments Fragments Main idea : Similar to defining an Activity Except main override for Activity is oncreate() For Fragment use : oncreateview() // check the savedinstancestate // inflate the layout onstart() // can now update view components since layout is ready for use // perform any initialisation and restoration of state

12 Managing Fragments Fragments The host activity is responsible for : Creating, adding and removing fragments Note : To be visible each Fragment must be added to a View Within the Fragment code, Save any state by overriding onpause() or onsavedinstancestate()

13 Programming with Fragments Note : communication between sibling fragments is not allowed* Instead communicate via parent activity Also, see examples here : fragments/fragment-ui.html cardflip.html Question : There is nothing to stop you trying this, but why do you think it is not allowed" Question : Do you need more than one activities in your app? Why not just stick to fragments?

14 XML Fragments - loading

15 Programmatically Fragments

16 Sensor Fragments Running on the device directly don t make much sense in the emulator But you can debug directly in your device

17 Sensor Fragments Running on the device directly (You may have already tried it) Enable developer mode on the device (device specific) Connect your device to your computer s USB port Setup your computer Install Drivers (if on windows) Run adb server as root / check lsusb for device in linux run?adb devices? Use the IDE to launch your app for the device

18 Android Sensor Categories Motion sensors : accelerometers, gravity sensors, gyroscopes, and rotational vector sensors Environmental sensors : barometers, photometers, and thermometers Position sensors : orientation sensors and magnetometers All sensors types defined in android.hardware.sensor : sensors_overview.html

19 Android Sensor Categories Motion TYPE_ACCELEROMETER TYPE_GYROSCOPE TYPE_ROTATION_VECTOR TYPE_GRAVITY TYPE_LINEAR_ACCELERATION All sensors types defined in android.hardware.sensor : sensors_overview.html

20 Android Sensor Categories Environmental TYPE_AMBIENT_TEMPERATURE TYPE_LIGHT TYPE_MAGNETIC_FIELD TYPE_PRESSURE TYPE_RELATIVE_HUMIDITY TYPE_TEMPERATURE All sensors types defined in android.hardware.sensor : sensors_overview.html

21 Android Sensor Categories Position TYPE_ORIENTATION TYPE_PROXIMITY All sensors types defined in android.hardware.sensor : sensors_overview.html

22 Finding available sensors Fragments

23 Listening to sensor events Within an activity that implements SensorEventListener

24 Handling multiple event types One could possibly do SenserEvent.sensor.getType() == Sensor.TYPE_ACCELEROMETER Use if/switch statements Or register multiple listeners Use-case specific Group similar events together

25 How/when to use sensors drain battery Some sensors drain more than other (e.g. Gyroscope vs Accelerometer) Not all devices have all kinds of sensors Device does not have a a type of sensor, getdefaultsensor returns null

26 Course outline/structure was based on Spyros Samothrakis s 2015 Course Course outline/structure was based on Simon Lucas s 2014 Course