Week 3 Class 1

First Android App

Goal of Today

Concepts for Today

1. Optionals in Kotlin -> Explained (Run time vs compile error))

2. Using Libraries in Android (Library vs Framework)

3. Android App UI -> Image set with a button

4. Declarative vs Imperative Programming?

5. XML vs Compose?

6. Lamda in Kotlin

Why this batch is most important?

Learn how to learn: XML + Compose -> 2022

Errors will come but we will fix together LIVE

Spots -> error

Rs. 1000

Steps to take

1. Designing the App: Figma

2. Why Declarative vs Imperative Approach?

3. Importing Libraries

4. Build and run

COding means handling errors, even when I recreate an app you will see errors and I will fix with you all

Homework Discussion

Read about Retrofit

Library vs Framework?

Android Revision (week2)

Constraint Layout

ImageView

Button Click

Declarative Programming vs Imperative Progamming

Imperative Programming

code: + how it is done?

// how to print list from list container? 4 lines of code

list = [1,2,3,4,5]

for x in list {

print(x)

}

Declarative

Answer using what -> / 1 line of code

getList()

12345

SQL -> Declarative

Select * from Employee

Why Declarative + Imperative

Why Compose + XML?

90%+ of Industry

Compose vs XML?

Compile-Time vs Run-Time Error

Which is Better?

lateinit var vs null object



Initialization	Property is uninitialized until explicitly initialized using lateinit.	Property is initialized to null by default.
Nullable Property	No need for a ? after the property type, as it's not nullable.	Property is implicitly nullable (requires ? after the property type).
Null Safety	Risky if not properly initialized; accessing an uninitialized lateinit property will result in a runtime exception.	Safe by default, as properties are initialized to null. Null checks or safe calls (?.) are required when accessing.
Initialization Responsibility	Developer must ensure that the property is initialized before use.	No obligation to explicitly initialize the property; it can remain null.
Use Cases	- Used when you can guarantee that the property will be initialized before being accessed. - To avoid nullable types and null checks, especially for properties that are expected to always have a value.	- Used when there's a possibility that the property might not be initialized immediately or can be left as null intentionally. - When you need to handle null values explicitly.

Revision: 3 types of Functions

Simple Lamda Example

typealias Callback = (String) -> Unit

fun performTask(callback: Callback) {
    // Simulating some task
    val result = "Task completed successfully"
    callback(result)
}

fun main() {
    performTask { result ->
        println("Callback received: $result")
    }
}

import java.util.function.Consumer;

interface Callback {
    void onComplete(String result);
}

class Task {
    void performTask(Callback callback) {
        // Simulating some task
        String result = "Task completed successfully";
        callback.onComplete(result);
    }
}

public class Main {
    public static void main(String[] args) {
        Task task = new Task();
        task.performTask(result -> System.out.println("Callback received: " + result));
    }
}

What are interfaces

Interface vs Class

Feature	Classes	Interfaces
Method Implementation	Can have method implementations	Only method signatures, no implementations
Inheritance	Single inheritance (extends one class)	Multiple inheritance (implements multiple interfaces)
Usage	Defines objects, properties, and behavior	Defines contracts for behavior
Abstraction	Abstraction of data and behavior	Higher level of abstraction, contract for behavior
Multiple Inheritance	Not supported	Supported (through implementing multiple interfaces)
Example	class MyClass { ... }	interface MyInterface { ... }

without Lamda

public class Main {
    public static void main(String[] args) {
        Adder adder = new Adder();
        int result = adder.add(5, 7);
        System.out.println("Result of adding 5 and 7 is: " + result);
    }
}

class Adder {
    public int add(int a, int b) {
        return a + b;
    }
}

fun main() {
    val add: (Int, Int) -> Int = { a, b -> a + b }

    val result = add(5, 7)
    println("Result of adding 5 and 7 is: $result")
}

with Lamda in Kotlin

ImageView and set Image in Android

1. Which is faster to share Image: Base64 or Downloading?

2. Why use Glide?

Using Library: Glide

1. Never reinvent wheel

2. Use Documentations

3. Gradle import

https://github.com/bumptech/glide

Add Permission

Add internet permisson

  I  Root cause (1 of 1)
java.lang.SecurityException: Permission denied (missing INTERNET permission?)
at java.net.Inet6AddressImpl.lookupHostByName(Inet6AddressImpl.java:150)
at java.net.Inet6AddressImpl.lookupAllHostAddr(Inet6AddressImpl.java:103)
at java.net.InetAddress.getAllByName(InetAddress.java:1152)
at com.android.okhttp.Dns$1.lookup(Dns.java:41)
at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:178)
at com.android.okhttp.internal.http.RouteSelector.nextProxy(Ro