📱 Android Studio – Full Story Style Notes

Unit 1: Concepts of Android & Setup

1. What is Android?

Android = Operating System (like Windows for PC, but for mobiles).
Open-source → free for anyone to use or modify.
Developed by Google.

🔹 Example: Just like your bike needs an engine to run, your mobile needs Android to run apps.

2. Features of Android

Open-source → anyone can create apps.
Connectivity → WiFi, Bluetooth, hotspot.
Multi-tasking → play music + chat.
Variety of Apps → Games, Banking, Shopping.
Notifications → WhatsApp popups, Email alerts.

🔹 Example: Your phone is like a supermarket — you can have many different stalls (apps) working together.

3. Android Architecture (Think of it as a layered cake 🎂)

Linux Kernel (Base layer) → Controls hardware (camera, battery, WiFi).
- Example: The foundation of a house.
Libraries → Pre-made code for features (database, web, graphics).
- Example: Kitchen tools like oven, mixer — help in cooking fast.
Android Runtime (DVM/ART) → Converts code into something the mobile understands.
- Example: Netflix reducing HD video size so it runs smoothly on your phone.
Application Framework → Provides services to apps (manages activities, resources).
- Example: A manager in a restaurant who coordinates waiters.
Applications → End-user apps like WhatsApp, Instagram.
- Example: Customers enjoying the food at the restaurant.

4. Dalvik Virtual Machine (DVM)

Special “mini-computer” that runs Android apps in small memory.
Optimized for mobiles (low RAM, small battery).

5. Android Emulator & AVD

Emulator → Fake phone running on your laptop.
AVD (Android Virtual Device) → The test phone you set up inside the emulator.

🔹 Example: Think of emulator as “acting like a phone” inside your computer, so you can test your app without buying a new device.

Unit 2: Creating Basic App

1. Activity

One screen of your app.
🔹 Example: WhatsApp chat screen, call screen, status screen → each is an Activity.

2. Layout

How things look on the screen → buttons, images, text fields.
🔹 Example: Arranging sofa, TV, and chairs in your living room = layout.

3. AndroidManifest.xml

Like the Aadhaar card of your app.
Tells Android:
- Who you are (app name, package name).
- What permissions you need (camera, internet).
  🔹 Example: If your app is a shop, Manifest is the shop license that allows it to operate.

4. R.java

Auto-created file that connects app resources.
🔹 Example: Like your phone contacts. Instead of dialing 9876543210, you just click on “Mom”.

Unit 3: XML (Extensible Markup Language)

Used to design UI layouts and store data.
Looks like HTML but stricter.

🔹 Example:


<Button text="Click Me!" />

Shows a button on screen.

Rules:
- Tags must open & close (<tag></tag>).
- Case-sensitive.
- One root element (like <LinearLayout>...</LinearLayout>).

🔹 Example: Think of XML as the blueprint of a house → it doesn’t build the house, but tells workers how it should look.

Unit 4: Android Widgets (UI Basics)

Title bar → Can hide it for fullscreen apps (like YouTube).
Orientation → Portrait (vertical) / Landscape (horizontal).
Button & onClick Event → Tap to do something.
🔹 Example: WhatsApp “Send” button sends your text.
Toast → Small popup messages.
🔹 Example: “Message deleted” or “Copied to clipboard.”
ToggleButton → Switch ON/OFF.
🔹 Example: WiFi switch in settings.

Unit 5: Other Widgets (UI Advanced)

CheckBox → Select multiple things.
🔹 Example: Pizza order → Cheese + Olives + Corn.
RadioButton → Choose one option only.
🔹 Example: Payment → UPI OR Card OR Cash.
Spinner (Dropdown) → Select from list.
🔹 Example: Select your city (Surat, Mumbai, Delhi).
AlertDialog → Popup asking confirmation.
🔹 Example: “Are you sure you want to exit?”
AutoCompleteTextView → Suggests while typing.
🔹 Example: Google search bar.
TextWatcher → Watches text changes.
🔹 Example: OTP auto-verifies when you type last digit.

🎯 Memory Hacks

Activity = Screen (like different WhatsApp screens)
Layout = Arrangement (like arranging chairs in a room)
Manifest = Aadhaar card of app
Toast = Popup message
CheckBox = Multi-choice pizza toppings
RadioButton = One-choice payment method
Spinner = Dropdown menu
AutoComplete = Google suggestions
TextWatcher = OTP auto verify

:::::::IMPORTANT QUESTION ANSWERS ARE AS FOLLOWS::::::

1. What is Android? Write its features and advantages of open-source.
- Android → Open-source OS by Google for mobile devices.
- Features: Multitasking, rich UI, connectivity (WiFi, Bluetooth), app store, security, cloud sync.
- Open-source advantages: Free to use, customizable, huge community support, faster innovation.
2. Explain Android architecture with a neat diagram.
Layers:
1. Linux Kernel – hardware drivers.
2. Libraries + Android Runtime (ART/DVM) – SQLite, SSL, graphics.
3. Application Framework – Activity Manager, Content Providers.
4. Applications – SMS, Camera, Contacts, User apps.
(Draw 4 stacked layers in exam.)

3. What is Dalvik Virtual Machine (DVM) / ART? Why is it required?
- DVM: Executes .dex files, optimized for low memory.
- ART (Android Runtime): Uses AOT (Ahead of Time) compilation, better performance.
- Required: Runs Java code on mobile efficiently.
4. Define Activity and explain Activity lifecycle methods.
- Activity: Screen/UI in Android app.
- Lifecycle:
  - onCreate() – init
  - onStart() – visible
  - onResume() – interactive
  - onPause() – partially hidden
  - onStop() – invisible
  - onDestroy() – end
  - onRestart() – restart after stop
5. What is Layout? Explain different types with examples.
- Layout = UI structure.
- Types:
  - LinearLayout (arrange vertically/horizontally).
  - RelativeLayout (position relative to parent/others).
  - ConstraintLayout (flexible constraints).
  - FrameLayout (stack views).
  - TableLayout (rows/columns).
6. Purpose of AndroidManifest.xml with example entries.
- Stores app info (permissions, components, hardware).
  Example:
```
<manifest ...>
  <application android:label="MyApp">
    <activity android:name=".MainActivity"/>
  </application>
  <uses-permission android:name="android.permission.INTERNET"/>
</manifest>
```
7. What is R.java? How does it connect resources to code?
- Auto-generated class → gives unique IDs to resources (layouts, strings, drawables).
- Example: R.layout.activity_main connects XML to Java.
8. What is XML? Write a sample XML layout for Button and TextView.
- XML → Markup language to design UI.
  Example:
```
<LinearLayout ...>
  <TextView android:text="Hello" android:id="@+id/tv"/>
  <Button android:text="Click" android:id="@+id/btn"/>
</LinearLayout>
```
9. What is a Toast? Write code to display a Toast on button click.
- Small popup message.
```
btn.setOnClickListener(v -> 
 Toast.makeText(this, "Button Clicked", Toast.LENGTH_SHORT).show());
```
10. Explain ToggleButton with attributes and event methods.
- Button with ON/OFF states.
- XML:
```
<ToggleButton android:id="@+id/toggle" android:textOn="ON" android:textOff="OFF"/>
```
- Java:
```
toggle.setOnCheckedChangeListener((b, checked) -> {});
```
11. Differentiate CheckBox, RadioButton, and ToggleButton with examples.
- CheckBox → Multiple selection (e.g., Pizza toppings).
- RadioButton → Single choice in group (e.g., Gender).
- ToggleButton → Switch ON/OFF (e.g., WiFi).
12. What is Spinner? Write steps/code to implement it.
- Dropdown menu.
  Steps:
1. Define <Spinner> in XML.
2. Create array in strings.xml.
3. Use ArrayAdapter.
```
Spinner sp = findViewById(R.id.spinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
 R.array.items, android.R.layout.simple_spinner_item);
sp.setAdapter(adapter);
```
13. What is AlertDialog? How to create a Yes/No confirmation dialog?
- Dialog box for alerts.
```
new AlertDialog.Builder(this)
  .setTitle("Confirm")
  .setMessage("Are you sure?")
  .setPositiveButton("Yes", (d,i)->{})
  .setNegativeButton("No", null)
  .show();
```
14. Explain AutoCompleteTextView with an example.
- Suggests options as user types.
```
AutoCompleteTextView ac = findViewById(R.id.ac);
String[] names = {"India","Indonesia","USA"};
ArrayAdapter<String> adapter = new ArrayAdapter<>(this,
 android.R.layout.simple_list_item_1, names);
ac.setAdapter(adapter);
```
15. Explain TextWatcher with a real-life use case (e.g., OTP auto-verify).
- Monitors text changes in EditText.
```
edit.addTextChangedListener(new TextWatcher() {
 public void afterTextChanged(Editable s) {
   if(s.length()==6) verifyOTP(s.toString());
 }
 public void beforeTextChanged(CharSequence c,int a,int b,int d){}
 public void onTextChanged(CharSequence c,int a,int b,int d){}
});
```

SpiceSaga

Tuesday, 16 September 2025

Android/ Application Summery of whole syllabus in short~