Android development is the process of building applications (apps) for devices running the Android Operating System (OS).

• Android apps are packaged as APK (Android Package) files

• APK contains:

  • Code
  • Resources
  • Assets

👉 Developers upload APKs to the Google Play Store for distribution.

The Android SDK is a collection of tools required to build Android applications.

• Provides APIs, libraries, and debugging tools
• Helps in building, testing, and managing apps
• Fully supported by Google and the developer community

In this course, we will learn:

1. Kotlin Programming Language
2. Android Studio (IDE)
3. Android Ecosystem
4. Core Android Components
5. Building Real Android Applications
6. Publishing Apps on Play Store

Jetpack Compose is a modern toolkit for building native Android UI.

• Less code
• Powerful tools
• Intuitive Kotlin APIs

👉 UI is created using @Composable functions in Kotlin 👉 No need for XML layouts

Kotlin is a statically typed, open-source programming language.

• Supports OOP + Functional Programming
• Runs on JVM (Java Virtual Machine)
• Interoperable with Java

Similar to Java, C#, and Scala

• Static Language: Variable type is determined at compile time
• Dynamic Language: Variable type is determined at runtime

• Fully interoperable with Java
• Easy conversion between Java ↔ Kotlin
• Built-in Java-to-Kotlin converter in Android Studio

• Less code
• Faster development
• Clean and readable syntax
• Supports Web, Desktop, and Android development

• Package: Organizes related classes
• Class: Blueprint for objects
• Object: Instance of a class (contains properties + functions)
• OOP: Programming based on objects and data
• Function: Reusable block of code
• Parameter/Argument: Value passed to a function

• JDK: Development tools
• JRE: Runtime environment
• JVM: Executes Java/Kotlin programs

Used to arrange UI components:

• Row → Horizontal layout
• Column → Vertical layout
• Box → Stack layout (overlapping elements)

👉 Main Direction = Arrangement 👉 Cross Direction = Alignment

• horizontalArrangement
• verticalAlignment

• verticalArrangement
• horizontalAlignment

• Start
• End
• Center
• SpaceBetween
• SpaceAround
• SpaceEvenly

• Top
• CenterVertically
• Bottom

• Top
• Bottom
• Center
• SpaceBetween
• SpaceAround
• SpaceEvenly

• Start
• CenterHorizontally
• End

Spacer is used to create empty space between UI components.

• Fixed space → width(), height(), size()
• Flexible space → weight()

• Add spacing between elements
• Push components apart
• Control layout spacing

A Button is a clickable UI component used to perform actions.

Button(onClick = { }) {
    Text("Click Me")
}

• onClick → Action handler
• modifier → Layout & styling
• colors → Button colors
• enabled → Enable/disable button
• shape → Corner design
• elevation → Shadow
• border → Outline
• content → UI inside button

TextField is used to take input from the user.

var text by remember { mutableStateOf("") }

• value → Current text
• onValueChange → Updates text
• label → Hint text
• modifier → Layout control
• colors → Styling

When state changes, Compose automatically updates only the affected UI.

👉 No manual UI refresh required

Modifiers are used to customize UI elements.

Modifier
    .fillMaxWidth()
    .padding(16.dp)
    .background(Color.Gray)

👉 Modifiers can be chained together

Used to display images from different sources:

• Drawable resources
• Bitmap
• Painter
• URL (using libraries like Coil)

• painter
• contentDescription
• modifier
• contentScale
• alignment

A CheckBox is a two-state component:

• Checked
• Unchecked

Used for selections and user input.

A Switch in Jetpack Compose is a UI component used to toggle between two states — ON and OFF. It is commonly used in settings screens for enabling or disabling features.

It works using a boolean state (true or false) and updates through the onCheckedChange callback when the user interacts with it.

• Stateful: Manages its own state
• Stateless: Receives state from outside

DropdownMenu is used in Jetpack Compose to display a list of selectable menu items in a popup menu.

• expanded → Controls whether the menu is visible or hidden.
• onDismissRequest → Called when the menu should close (outside click/back press).
• modifier → Used to style or position the menu.
• offset → Changes the menu position relative to its anchor.
• properties → Controls additional popup behavior.

DropdownMenuItem represents a single selectable option inside a DropdownMenu.

• text → Displays the content/text of the item.
• onClick → Executes when the item is selected.
• leadingIcon → Adds an icon at the start.
• trailingIcon → Adds an icon at the end.
• enabled → Enables or disables item selection.
• colors → Customizes item colors.
• contentPadding → Adjusts spacing inside the item.

A Toast Message is a small popup message used to show short feedback to the user. It appears for a short time and disappears automatically without user action.

• context -> Defines where the Toast will be shown from.
• "message" -> The text that is displayed inside the Toast.
• "Duration" -> Defines how long the Toast will be visible.
• show() -> Displays the Toast message on the screen.

A Snackbar Message is a message shown at the bottom of the screen to give feedback to the user. It can also include an action button such as Undo, Retry, or Dismiss.

• snackbarHostState -> Controls and manages the Snackbar message.
• SnackbarHost -> Defines the place where the Snackbar will be displayed.
• message -> The text displayed inside the Snackbar.
• actionLabel -> Adds an action button inside the Snackbar.
• "duration" -> Defines how long the Snackbar will stay visible.
• showSnackbar() -> Displays the Snackbar message.
• "CoroutineScope" -> Required because showSnackbar() is a suspend function.