Loeng 5

Transcript

1. Indrek Kõue indrek.koue@itcollege.ee MOBILE SOFTWARE DEVELOPMENT FOR ANDROID Lecture 5 i397 www.applaud.ee 2015 kevad
2. TOPICS Sensors Runtime configuration change Project dependencies View adapters Rest services JSON parsing
3. REHERSAL Local data storage • Shared Preferences • Internal storage • External storage • SQLite database + ORM Positioning
4. SENSORS Motion • gravity • gyroscope Postion • proximity • megnetometer Environmental • barometer • photometer • thermometer • humidity Note! All sensors are optional.
5. MOTION SENSORS Gravity sensor (accelerometer) Measures linear acceleration based on vibration on X, Y and Z axis. Unit: m/s2 Gyroscope Detects the current orientation of the device, or changes in the orientation Unit: rad/s
6. POSITION SENSORS Proximity sensor Laser sensor which senses if something is close to front side of the phone. Unit: binary (close, not close) or cm Magnetometer Measures the strength of earth’s magnetic field Unit: tesla [T]
7. ENVIRONMENT SENSORS Barometer Air pressure. Unit: Pascal Photometer Amount of light. Used for calibrating screen brightness. Unit: Lux Thermometer Battery temperature and/or ambient temperature. Unit: °C Humidity Measures the relative ambient humidity. Unit: %
8. public class SensorActivity extends Activity implements SensorEventListener { @Override public final void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); SensorManager mSensorManager = (SensorManager) getSystemService( Context.SENSOR_SERVICE); Sensor mLight = mSensorManager.getDefaultSensor(Sensor.TYPE_LIGHT); if(mLight == null){ //don't have light sensor } } @Override public final void onSensorChanged(SensorEvent event) { float lux = event.values[0]; } //register listener in onResume }
9. SENSORS @Override protected void onResume() { super.onResume(); mSensorManager.registerListener(this, sensor, SensorManager.SENSOR_DELAY_NORMAL); } @Override protected void onPause() { super.onPause(); mSensorManager.unregisterListener(this); }
10. RUNTIME CONFIGURATION CHANGE Configuration of app changes on runtime. Most commonly portrait > landscape > portrait. Activity is destroyed, but you can prevent this: <activity android:name=".MyActivity" android:configChanges="orientation|screenSize" android:label="@string/app_name"> Downside: configuration specific layout won’t work (but you could override onConfigurationChanged(Configuration newConfig) in activity)
11. PROJECT DEPENDENCIES Adding .jar manually or Using Gradle/Maven
12. PROJECT DEPENDENCIES Adding .jar manually 1)download .jar 2)copy to project folder 3)reference local file in build.gradle dependencies { compile files('libs/something_local.jar') } Downsides: • time consuming • it is not recommended to host large binaries in code repository
13. PROJECT DEPENDENCIES Using Gradle/Maven 1)add Gradle/Maven resource url to gradle.build Example: compile 'com.google.code.gson:gson:2.3.1' Downsides: • can't clean or first compile project without internet connection • when using unofficial dependency repo and repo goes down = problem
14. VIEW ADAPTERS Middleman between the data source and the layout Why? to create dynamic layouts Most popular: ArrayAdapter
15. VIEW ADAPTERS ArrayAdapter(Context context, int resource, T[] objects) ArrayAdapter(Context context, int resource, int textViewResourceId, T[] objects) ArrayAdapter(Context context, int resource, List<T> objects) ArrayAdapter(Context context, int resource, int textViewResourceId, List<T> objects)
16. VIEW ADAPTERS ArrayList<String> list = new ArrayList<>(); list.add(“first”); list.add(“second”); list.add(“third”); ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, list); ListView listView = (ListView) findViewById(R.id.listview); listView.setAdapter(adapter);
17. VIEW ADAPTERS CLICK LISTENING // Create a message handling object as an anonymous class. private OnItemClickListener handler= new OnItemClickListener() { public void onItemClick(AdapterView parent, View v, int position, long id) { // Do something in response to the click } }; listView.setOnItemClickListener(handler);
18. VIEW ADAPTER UPDATE LIST notifyDataSetChanged () Triggers a complete redraw of all (visible) children at once ArrayList<String> list = new ArrayList<>(); list.add(“first”); ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, list); ListView listView = (ListView) findViewById(R.id.listview); listView.setAdapter(adapter); //in some other callback list.add(“second”); listView.getAdapter().notifyDataSetChanged();
19. LISTVIEW
20. GRIDVIEW
21. ADVANCED: CUSTOM VIEW ADAPTER override getView() in adapter to return a custom view
22. public class CustomUsersAdapter extends ArrayAdapter<User> { public CustomUsersAdapter(Context context, ArrayList<User> users) { super(context, 0, users); } @Override public View getView(int position, View convertView, ViewGroup parent){ // Get the data item for this position User user = getItem(position); View view = LayoutInflater.from(getContext()). inflate(R.layout.item_user, parent, false); TextView tvName = (TextView) v.findViewById(R.id.tvName); TextView tvHome = (TextView) v.findViewById(R.id.tvHometown); tvName.setText(user.name); tvHome.setText(user.hometown); return view; } }
23. ADVANCED: PERFORMANCE OPTIMIZATION 1)reusing already inflated view convertView in getView() 2)viewholder pattern reusing references to resources in inflated view using custom class Recycling of views is a very useful: saves CPU + memory
24. ADVANCED: PERFORMANCE OPTIMIZATION
25. public class CustomUsersAdapter extends ArrayAdapter<User> { public CustomUsersAdapter(Context context, ArrayList<User> users) { super(context, 0, users); } @Override public View getView(int position, View convertView, ViewGroup parent) User user = getItem(position); // Check if an existing view is being reuse if (convertView == null) { convertView = LayoutInflater.from(getContext()). inflate(R.layout.item_user, parent, false); } // Lookup view for data population TextView tvName = (TextView) convertView.findViewById(R.id.tvName) TextView tvHome = (TextView) convertView.findViewById(R.id.tvHomet tvName.setText(user.name); tvHome.setText(user.hometown); return convertView; } }
26. RECYCLER VIEW Replacement for ListView Released with Android 5.0 Benefits: • Tighter integration of viewholder pattern (caching) • Better animation support Can use in older versions through support library: dependencies { compile 'com.android.support:recyclerview-v7:21.0.+' }
27. REST SERVICES HTTP GET/POST + JSON = REST service Stateless: HTTP server does not retain information or status for the duration of multiple requests = each time state parameters are passed by.
28. HTTP GET Request GET /blog/posts/1 Host: myblog.com Accept: application/json Response: HTTP/1.1 200 Success Content-Type: application/json Content-Length: 65 {"id":"1","title":"Hello World!","body":"This is my first post!"}
29. HTTP POST Request POST /blog/newpost Host: myblog.com Accept: application/json Content-Type: application/json {"title":"Hello World!","body":"This is my first post!"} Response: HTTP/1.1 201 Created
30. JSON { "name": "John", "surname": "Doe", "cars": [ { "manufacturer": "Audi", "model": "A4", "capacity": 1.8, "accident": false }, { "manufacturer": "Škoda", "model": "Octavia", "capacity": 2, "accident": true } ], "phone": 245987453 }
31. JSON public class Person { private String name; private String surname; private Car[] cars; private int phone; private int age; private Person() { } }
32. JSON PARSING The hard way: manually String json = loadJsonFromHttpUrl(“http://….”); JSONObject jObj = new JSONObject(json); Person person = new Person(); person.name = jObj.getString("name"); person.surname = jObj.getString("surname"); person.phone = jObj.getInt("phone"); person.age = jObj.getInt("age"); JSONArray jArr = jObj.getJSONArray("cars"); for (int i=0; i < jArr.length(); i++) { JSONObject obj = jArr.getJSONObject(i); Car car = new Car(); car.manu………... }
33. JSON PARSING The efficient way: auto deserializer String json = loadJsonFromHttpUrl(“http://….”); Gson gson = new Gson(); Person johnDoe = gson.fromJson(json, Person.class); Most popular libraries: Gson, Jackson
34. READING FOR HOME http://developer.android.com/guide/topics/resources/runtime-changes.html http://en.wikipedia.org/wiki/JSON http://en.wikipedia.org/wiki/Representational_state_transfer http://developer.android.com/training/improving-layouts/smooth-scrolling. html
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