The document discusses using AsyncTask in Android to perform background operations and update the UI thread. It provides an example of using AsyncTask to fetch distance data from the Google Distance Matrix API in the background. Some key points: 1. AsyncTask allows performing operations in the background using doInBackground() and updating the UI using onPostExecute(). 2. The example API call is made in doInBackground() and the results are extracted from the JSON response. 3. OnPostExecute() receives the results and updates the UI by setting the distance text on button click. 4. Accessing APIs involves getting a JSONObject from the response and extracting the required values using JSON tags. 5

1. HELLO
DIVING INTO DAY FIVE

2. AsyncTask

3. Simple AsyncTask

Basic UI:
−

TextView, EditText
and Button
Goal: To display the
input typed in by the
user in the free space
below.
Timer here will call a thread that
delays the execution of the AsyncTask

4. Simple AsyncTask

Call the AsyncTask on button click:
execute.setOnClickListener(new
View.OnClickListener() {
@Override
Implementing an AsyncTask
with parameters
public void onClick(View arg0) {
// TODO Auto-generated method stub
new
ViewFiller().execute(input.getText().toSt
ring(), timer.getText().toString());
}
});
execute here is the button shown in the earlier layout

5. AsyncTask


Perform operations on a different thread.
Used to prevent heavy processing from
freezing the UI
and also do this

6. How do we do this ?


We create a class inside our Activity that
extends the AsyncTask
We use different methods it offers do perform
operations in the background:
−
OnPreExecute()

−
doInBackground(Params... )

−
Generally used to load the progress bar
All the logic is dumped here
OnProgressUpdate()

Called when publishProgress() is called in the
doInBackground()
−
onPostExecute(Result)

Gives out the desired results

7. ViewFiller extends AsyncTask
public class ViewFiller extends
AsyncTask<String, Integer, String> {
//code here
}
What are the parameters
being defined here ?

8. 
AsyncTask<Params, Progress, Result>
−Params:
the input, what you pass into the AsyncTask
−Progress:
−Result:
on updates, passed to onProgressUpdate()
the output from doInBackground() returned to
the onPostExecute()

9. onPreExecute
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
execute.setText("Running...");
displayProgress("Updating field ... ");
// Start the progress dialog
progress.show();
}

10. doInBackground
protected String doInBackground(String... input) {
try {
int time;
if (input[1].equalsIgnoreCase("")) {
time = 0;
} else {
time = Integer.parseInt(input[1]) * 1000;
for (int i = 1; i <= time / 1000; i++) {
publishProgress(i, time);
Thread.sleep(1000);
}
Call to onProgressUpdate
}
} catch (InterruptedException e) {
e.printStackTrace();
}
return input[0];
}
Passing parameter to onPostExecute

11. onProgressUpdate
@Override
protected void onProgressUpdate(Integer...
values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
displayProgress("Updating field ... " +
values[0] + " of "+ values[1] / 1000);
}
Interaction with the UI

12. onPostExecute
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
execute.setText("Execute");
progress.dismiss();
tvInput.setText(result);
}
Full code: http://bit.ly/1eG57hY

13. Deeper with AsyncTask

The first think you should understand:
−
They rely on Java concepts of GENERICS and
VARARGS
GENERICS:

Can declare of any type
VARARGS:

Arrays… you can pass in number of values

14. Adding AsyncTask to our app

15. @Override
protected void onCreate(Bundle
savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView)
findViewById(R.id.smsList);
progress = (ProgressBar)
findViewById(R.id.progress);
cursor = dbAdapter.getAllRows();
new DBAsync().execute(cursor);
}

16. Class that extends the AsyncTask
public class DBAsync extends AsyncTask <Cursor, String,
Cursor>{
// code here
}

17. onPreExecute
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
//Declare progress as a global variable
progress = new ProgressDialog(Registration.this);
progress.setProgressStyle(ProgressDialog.STYLE_SPINNER
);
progress.setMessage("Loading from Database ...");
progress.show();
}

18. doInBackground
@Override
protected Cursor doInBackground(Cursor...
cursor) {
// TODO Auto-generated method stub
return cursor[0];
}

19. onPostExecute
@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
progress.dismiss();
String[] from = new String[] { dbAdapter.KEY_ROWID,
dbAdapter.KEY_NAME, dbAdapter.KEY_ADD };
int[] to = new int[] { R.id.list_id, R.id.list_name,
R.id.list_address };
SimpleCursorAdapter adapter = new
SimpleCursorAdapter(getApplicationContext(),
R.layout.result_layout, result, from, to, 1);
listView.setAdapter(adapter);
}

20. On click event on ListView
listView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
// TODO Auto-generated method stub
This view is the parameter
defined in the onItemClick method
TextView refId = (TextView)view.findViewById(R.id.list_id);
TextView refName = (TextView)view.findViewById(R.id.list_name);
TextView refAdd = (TextView)view.findViewById(R.id.list_address);
String sd_id = refId.getText().toString();
String sd_name = refName.getText().toString();
String sd_add = refAdd.getText().toString();
buildAlert(sd_id, sd_name, sd_add);
}
});
Method to create an AlertDialog

21. BuildAlert Method
public void buildAlert(String id, String name, String add){
We also have to create the
AlertDialog dialog = new
AlertDialog.Builder(ClassName.this).create(); object prior to declaring it
refers to
default android resources
dialog.setIcon(android.R.drawable.ic_dialog_info);
dialog.setTitle("View on Alert Dialog");
dialog.setMessage("id = "+id+"; name = "+name+"; address = "+add);
dialog.setButton(DialogInterface.BUTTON_POSITIVE, "OK", new
DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,
int which) {
dialog.dismiss();
return;
}
});
POSITIVE, NEGATIVE and NEUTRAL all
contribute to the positioning of the buttons.
Till Honeycomb, the button order
(left to right) is POSITIVE - NEUTRAL - NEGATIVE.
On newer devices, the button order
(left to right) is now NEGATIVE - NEUTRAL - POSITIVE.
dialog.show(); Always remember to show me :)

22. 
Another example using the AsyncTask and
SimpleCursorAdapter:
http://bit.ly/17ipnE4

23. TYPES
OF MOBILE APPS

24. Mobile Apps

Two categories of mobile apps:
−
View-heavy (data-driven)

−
Graphics-heavy (drawing-based)


Social, news.
Games, photo editing.
Focus on data-driven
−
Heart of mobile development
−
Graphics-heavy are more specialized and more
advanced.

25. Data driven apps
Instagram
Tumblr
Facebook

26. Developing View-Heavy apps

Making view-heavy apps rest on a few core
concept
−
Common controls and View Layout

−
Interaction and event handling

−
Application's overall structure.
Data modeling, Networking and Persistence

−
All the touch interactions made by users.
Screen flows and Navigation

−
Android's view system.
Network requests (API interaction), data storage.
Accessing the mobile features

27. API interaction

Interaction through
−
XML


−
Java parser: SAX and the DOM XML parsers
Android provides XmlPullParser which is less
complicated.
JSON

JSONObject and JSONArray are used.

28. Accessing HTTP

There are two ways of accessing HTTP in
android:
−
Using the HttpURLConnection

−
Using the HttpClient


Using the HttpURLConnection object and its method
Use DefaultHttpClient, Http GET & POST,
HttpResponse, HttpEntity
Both of these follow similar steps:
−
Process the Http input
−
Use InputStream and BufferedReader to iterate
through the http output.

29. DistanceMatrix API

URL –
http://maps.googleapis.com/maps/api/distancematrix/json
?params

Parameters:
−
origins

−
destinations

−
origins=Jamal,Kathmandu
destinations=Kalanki,Kathmandu
sensor

sensor=false

30. API Response

31. Application UI
Call on the
AsyncTask
on click
Do NOT FORGET to use
the INTERNET permission

32. 
How do we implement this ?
−Get
the JSONObject
−Extract
Results from the API's response
−Putting
it all together

33. Get the JSONObject

Create a HTTPClient
−

Use the HTTPGet
−

HttpGet httpGet = new HttpGet(url);
Get the HTTPResponse
−

DefaultHttpClient httpClient = new
DefaultHttpClient();
HttpResponse httpResponse =
httpClient.execute(httpGet);
Get the HTTPEntity to an InputStream
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();
// InputStream is

Pass the InputStream to a BufferedReader

Convert the output to a JSONObject

34. Extracting results from the API's
response

To get the JSON output we use:
−
JSONObject

−
'{'
represents the JSONObject
JSONArray

'[' represents the JSONArray

35. JSONObject
JSONArray

36. Accessing JSON
JSONObject googleObject1, googleObject2, googleObject3, googleObject4;
JSONArray googleArray1, googleArray2;
...
String distanceBetween = "";
try{
//Getting array of the API
UserFunctions users = new UserFunctions();
googleObject1 = users.distanceGET(places[0], places[1]);
//places[0] and places[1] are values passed on button click
googleArray1 = googleObject1.getJSONArray(TAG_ROW);
googleObject2 = googleArray1.getJSONObject(0);
googleArray2 = googleObject2.getJSONArray(TAG_ELEMENTS);
googleObject3 = googleArray2.getJSONObject(0);
googleObject4 = googleObject3.getJSONObject(TAG_DISTANCE);
distanceBetween = googleObject4.getString(TAG_TEXT);
}catch(JSONException e){
e.printStackTrace();
Full code: http://bit.ly/HTGTm1

37. Putting it all together




A separate class is created to convert the URL
response to a JSONObject
Button click triggers the AsyncTask where inputs
for the doInBackground() are stated
All the accessing/references to the API is done
in the AsyncTask, where the main logic lies in
the doInBackground()
returns results to the
onPostExecute() where it refreshes the UI
thread
doInBackground()

38. SharedPreferences

39. Android Storage

How do you save your application data ?
−
SharedPreferences*

−
Internal Storage

−
Storage on shared external storage
SQLite Databases*

−
Storage on device memory
External Storage

−
Storage in key-value pairs.
Store structured data in a private database
Network Connections

Store data on web

40. SharedPreferences

The way android stores users preferences

But why SharedPreferences ?
−
Ease of implementation
−
Faster in terms of coding
−
Accessibility of key values
−
Suitable for the small things

e.g. Game difficulty level, user name, user accounts, etc.

41. SharedPreferences

Every thing is saved in terms of key-value
−
e.g. “NAME”, “Android”
“PhoneNumber”, “1234”

For the implementation we will be using the:
−
SharedPreferences
−
General framework to save and retrieve persistent keyvalue pairs
Editor



Interface used for modifying values in a
SharedPreferences object
Use of commit() or apply() to make changes persist

42. Implementation
public class ProjectPreference{
SharedPreferences pref;
We are creating a
separate class
here
Editor editor;
Context _context;
int PRIVATE_MODE = 0;
private static final String PREF_NAME = “prefmyapp”;
... (A)
public ProjectPreference(Context context){
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME,
PRIVATE_MODE);
editor = pref.edit();
} ... (B)

43. A: Define Variables

Suppose we have a contact to save:
−
−
Address
−

Name
Number
Declare them:
public static final String KEY_NAME = “name”;
public static final String KEY_ADD = “address”;
public static final String KEY_NUM = “number”;

44. B: Define Getters and Setters

Defining setters and getters
−
void for setters
public void setName(String key, String value){
editor.putString(key, value);
editor.commit();
}
−
<types> for getters
public String getName(String key){
return pref.getString(key, “”);
}
You can
define your default
values here

45. Accessing SharedPreferences

Create an object
ProjectPreference SM;

Initialize
SM = new ProjectPreference(Class.this);

Access variables and methods
SM.getName(SM.KEY_NAME);

Set values
SM.setName(SM.KEY_NAME, “Android”);

46. Building an application
Spinner
Make a simple application that
displays what the
user sets in the preferences page
onto the application's launcher activity

47. Spinner
<Spinner
...
android:entries="@array/colors" />
Defines the entries
inside Spinner
Declared in strings under
values

48. Spinner
<string-array
name="colors">
<item>Blue</item>
<item>Purple</item>
<item>Red</item>
<item>Orange</item>
<item>Green</item>
<item>Yellow</item>
<item>Black</item>
<item>White</item>
</string-array>

49. Building our application

In our MainActivity:
−
−
Call for the
SharedPreferences.
Check if there is any
value stored.
If yes:
Display the stored
value.
If no:
Call on another class
that allows users to
store value.
Full code: http://bit.ly/HKrhBm