course on Kotlin Android App Development, Creating Screens Using Jetpack

In Android development, the user interface (UI) is one of the core elements of an application.
To build it, various libraries and tools from Android Jetpack can be utilized.
In this article, we will explore in detail how to create screens using Jetpack Compose with Kotlin.

1. What is Jetpack Compose?

Jetpack Compose is a modern Android UI toolkit.
It uses a declarative UI paradigm to make it easier for developers.
This tool allows for quick UI building and dynamic updates.
It also provides compatibility with the existing XML layout system and has features that enable easy and intuitive composition of UI elements.

2. Advantages of Jetpack Compose

• Declarative UI: The UI automatically updates based on state.
• Modularity: UI components are divided into smaller, reusable units for management.
• Tooling support: Increases productivity through preview features and code refactoring support in Android Studio.

3. Getting Started with Jetpack Compose

To use Jetpack Compose, you need to update Android Studio to the latest version.
Additionally, you must set up Compose during project creation.

3.1. Creating a New Compose Project

1. Run Android Studio and select “New Project”.
2. Select the “Empty Compose Activity” template.
3. Enter the project name and package information, then click the “Finish” button to create the project.

3.2. Configuring build.gradle

Next, you need to configure the build.gradle file of the project.
It is necessary to add dependencies related to Compose.

dependencies {
    implementation "androidx.compose.ui:ui:1.0.0"
    implementation "androidx.compose.material:material:1.0.0"
    implementation "androidx.compose.ui:ui-tooling:1.0.0"
    implementation "androidx.activity:activity-compose:1.3.0"
}

4. Creating a Simple UI Screen

Now, let’s create a simple UI screen.
For example, we will implement user interaction through a basic button and text.

4.1. Constructing Basic UI

package com.example.myapp

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.material.Button
import androidx.compose.material.MaterialTheme
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.tooling.preview.Preview

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            MyApp {
                Greeting("Android")
            }
        }
    }
}

@Composable
fun MyApp(content: @Composable () -> Unit) {
    MaterialTheme {
        content()
    }
}

@Composable
fun Greeting(name: String) {
    Button(onClick = { /* Do something */ }) {
        Text(text = "Hello, $name!")
    }
}

@Preview(showBackground = true)
@Composable
fun DefaultPreview() {
    MyApp {
        Greeting("Android")
    }
}

5. UI Components of Compose

Compose provides various UI components. Here, we will explain some of the key components.

5.1. Text

You can use the Text composable to display text.
The following is an example that displays a string on the screen.

@Composable
fun DisplayText() {
    Text(text = "Hello, Jetpack Compose!")
}

5.2. Button

You can create a button to receive user input.
The code below is an example where the text changes when the button is clicked.

@Composable
fun ButtonExample() {
    var buttonText by remember { mutableStateOf("Please Click") }
    
    Button(onClick = { buttonText = "Clicked!" }) {
        Text(text = buttonText)
    }
}

5.3. Column

You can use the Column composable to arrange components vertically.

@Composable
fun ColumnExample() {
    Column {
        Text("First Text")
        Button(onClick = { /* Do something */ }) {
            Text("Second Text Button")
        }
    }
}

6. State Management

Jetpack Compose allows you to easily manage state-based UI components.
When the state changes, the UI updates automatically.
You can manage the UI’s state through remember and mutableStateOf.

6.1. State Example

@Composable
fun StatefulCounter() {
    var count by remember { mutableStateOf(0) }

    Column {
        Text(text = "Current Count: $count")
        Button(onClick = { count++ }) {
            Text(text = "Increase Count")
        }
    }
}

7. Design Composition

Jetpack Compose natively supports Material Design.
You can maintain a consistent design by using various Material UI components.

7.1. Using Material Theme

@Composable
fun ThemedApp() {
    MaterialTheme {
        Column {
            Text("Material Design Example", style = MaterialTheme.typography.h4)
            Button(onClick = { /* Do something */ }) {
                Text("Button")
            }
        }
    }
}

8. Navigation Management

Managing transitions between multiple screens is very important in Android app development.
In Jetpack Compose, it can be easily implemented using NavHost.

8.1. Adding Navigation Library

dependencies {
    implementation "androidx.navigation:navigation-compose:2.4.0"
}

8.2. Navigation Example

@Composable
fun SetupNavGraph() {
    val navController = rememberNavController()
    NavHost(navController, startDestination = "firstScreen") {
        composable("firstScreen") { FirstScreen(navController) }
        composable("secondScreen") { SecondScreen() }
    }
}

@Composable
fun FirstScreen(navController: NavController) {
    Column {
        Text("First Screen")
        Button(onClick = { navController.navigate("secondScreen") }) {
            Text("Go to Second Screen")
        }
    }
}

@Composable
fun SecondScreen() {
    Text("Second Screen")
}

9. Conclusion

Developing Android screens using Jetpack Compose is very powerful and intuitive.
With declarative UI, you can write UI more efficiently.
This article explained the basic screen composition components, state management, and navigation methods.
In the future, try developing various apps using Jetpack Compose.

Additionally, explore more features through the official documentation and various examples of Jetpack Compose.
You can visit the official Jetpack Compose documentation for more detailed information.