Asynchronous Data Handling, Networking and Files

Asynchronous Data Handling

Performing tasks in the background (non-UI thread) to keep UI smooth.

Why Needed?

• Avoid UI freezing (ANR – Application Not Responding)
• Handle network & database operations efficiently

Synchronous vs Asynchronous

Feature	Synchronous	Asynchronous
Execution	One after another	Parallel/background
UI Blocking	Yes	No
Speed	Slow	Faster

AsyncTask 

Performs background operations and updates UI.

Lifecycle of AsyncTask

onPreExecute()
      ↓
doInBackground()
      ↓
onProgressUpdate()
      ↓
onPostExecute()

Example

private class MyTask extends AsyncTask<Void, Void, String> {

    protected void onPreExecute() {
        // Before execution
    }

    protected String doInBackground(Void... params) {
        return "Data loaded";
    }

    protected void onPostExecute(String result) {
        textView.setText(result);
    }
}

Coroutines (Modern Approach)

Lightweight threads used in Kotlin for async programming.

Features

• Easy to read/write
• Less memory usage
• Structured concurrency

Coroutine Flow

Main Thread
    |
 launch{}
    |
 suspend function
    |
 Background Work

Example (Kotlin)

GlobalScope.launch {
    val data = fetchData()
    withContext(Dispatchers.Main) {
        textView.text = data
    }
}

Coroutine Dispatchers

Dispatcher	Use
Main	UI thread
IO	Network/DB
Default	CPU tasks

API Handling

Fetching data from server using HTTP methods.

Common Methods

Method	Purpose
GET	Retrieve data
POST	Send data
PUT	Update data
DELETE	Remove data

API Flow

App → HTTP Request → Server → JSON Response → UI

JSON Parsing

Converting JSON data into usable objects.

Example JSON

{
  "name": "Jay",
  "age": 25
}

Parsing Example (Java)

JSONObject obj = new JSONObject(jsonString);
String name = obj.getString("name");

JSON Types

Type	Example
Object	{ }
Array	[ ]
Key-Value	"name":"Jay"

Volley Library

Library for network requests.

Features

• Automatic caching
• Easy API calls
• Request queue

Volley Architecture

Request → Queue → Network → Response → UI

Example

RequestQueue queue = Volley.newRequestQueue(this);

StringRequest request = new StringRequest(Request.Method.GET, url,
    response -> textView.setText(response),
    error -> error.printStackTrace()
);

queue.add(request);

Retrofit Library

Type-safe HTTP client for Android.

Features

• Converts JSON to objects
• Easy API interface
• Supports coroutines

Retrofit Flow

Interface → Retrofit → API Call → Response → Model Class

Example

public interface ApiService {
    @GET("users")
    Call<List<User>> getUsers();
}

Volley vs Retrofit

Feature	Volley	Retrofit
Ease of Use	Medium	Easy
JSON Parsing	Manual	Automatic
Performance	Good	Excellent

File Handling in Android

Types

• Internal storage
• External storage

Write File

FileOutputStream fos = openFileOutput("file.txt", MODE_PRIVATE);
fos.write("Hello".getBytes());
fos.close();

Read File

FileInputStream fis = openFileInput("file.txt");

HTML Parsing

Extracting data from HTML content.

Example

Spanned html = Html.fromHtml("<b>Hello</b>");
textView.setText(html);

XML Parsing

Reading XML structured data.

Types

Parser	Description
DOM	Loads full XML
SAX	Event-based
Pull Parser	Efficient

Example (XML Pull)

XmlPullParser parser = Xml.newPullParser();

Broadcast Receivers

Responds to system-wide events.

Examples

• Battery low
• Network change

Flow

System Event → Broadcast Receiver → App Action

Example

public class MyReceiver extends BroadcastReceiver {
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Event Received", Toast.LENGTH_SHORT).show();
    }
}

Services

Runs in background without UI.

---

Types

Type	Description
Foreground	Visible to user
Background	Hidden
Bound	Linked to component

Service Lifecycle

onCreate()
   ↓
onStartCommand()
   ↓
Running
   ↓
onDestroy()

Example

public class MyService extends Service {
    public int onStartCommand(Intent intent, int flags, int startId) {
        return START_STICKY;
    }
}

Combined Architecture Diagram

UI
 |
Coroutine / AsyncTask
 |
API Call (Retrofit/Volley)
 |
JSON Parsing
 |
Database/File
 |
LiveData → UI

Important Exam Questions

Short Questions

• What is AsyncTask?
• Define Retrofit.
• What is Broadcast Receiver?

Long Questions

• Explain coroutines with example.
• Compare Volley and Retrofit.
• Describe Service lifecycle.

Practical Questions

• Write API call using Retrofit.
• Parse JSON data.
• Create Broadcast Receiver.

Final Summary

• AsyncTask → Old async method
• Coroutines → Modern async
• Retrofit/Volley → Networking
• JSON/XML → Data formats
• BroadcastReceiver → Events
• Service → Background tasks