Jetpack Compose: How to set background for a Row element

Introduction

In the world of Android development, Jetpack Compose has revolutionized the way developers build user interfaces. It offers a modern toolkit that simplifies UI creation through declarative programming, making it not only more efficient but also more intuitive. One of the key strengths of Jetpack Compose is its flexibility in creating complex layouts with minimal code. In this example, we'll explore how to work with Row components and apply background colors and gradients to them, demonstrating the power of Jetpack Compose in crafting visually appealing UIs.

This article breaks down an example of how to create a screen layout using Scaffold, Column, and Row composables. The main focus is on setting backgrounds for Row elements, including both solid colors and gradient backgrounds. By the end of this explanation, you'll gain a deeper understanding of how to leverage Jetpack Compose for building responsive and stylish user interfaces.

Understanding the Structure

The starting point of this application is the MainActivity, which serves as the entry point. Here, the onCreate() method sets the content view using the setContent function, where the GetScaffold() composable is called to build the UI. Jetpack Compose allows for this seamless integration by enabling you to define the entire layout within Kotlin code, eliminating the need for XML files.

The GetScaffold() composable leverages Jetpack Compose’s Scaffold component, which is an essential part of designing material-themed applications. This component helps organize different parts of the screen, such as the topBar, content area, and background color. In our example, a TopAppBar is used to display a title, while the main content is defined in a separate composable function called MainContent().

Creating the Main Content Layout

The MainContent() composable is where the primary layout is defined. A Column composable is used to arrange its child elements vertically. Within this column, two Row composables are placed, each designed to take up an equal amount of space thanks to the use of the weight modifier. This ensures that both rows are proportionally spaced within the screen.

The first Row demonstrates how to set a solid color as the background. By using the background() modifier with a specified Color object, the row is filled with a light blue shade. Additionally, the wrapContentSize() modifier centers the text within the row, ensuring that it is aligned neatly in the middle of its container.

Applying Gradient Backgrounds

In the second Row, we explore the use of gradient backgrounds, which can enhance the visual appeal of your application. The Brush.linearGradient() function is utilized to create a smooth color transition between multiple shades. In this example, the gradient transitions from orange to green to purple, giving the row a vibrant and dynamic look. Applying the gradient is as simple as using the background() modifier, but with a Brush instead of a solid Color.

The flexibility of Jetpack Compose's background() modifier allows developers to easily switch between solid colors and gradient backgrounds, making it highly adaptable for different design requirements. The wrapContentSize() modifier is used here as well to center the text within the row, maintaining a consistent alignment throughout the layout.

Previewing the Composables

To ensure that your composables look as expected before deploying the application, Jetpack Compose offers the @Preview annotation. Although the preview function in this example is commented out, it can be quickly enabled to visualize the GetScaffold() composable directly in Android Studio’s preview pane. This feature is incredibly useful for iterative development, as it allows you to see the changes in real-time without having to rebuild the entire application.

Summary

In this example, we demonstrated how to use Jetpack Compose to create a layout with background customization using Row components. We explored the use of solid color backgrounds as well as gradient backgrounds to create a visually appealing user interface. The use of composables like Scaffold, Column, and Row not only makes the code cleaner but also highly reusable, which is a significant advantage in modern Android development.

By mastering these techniques, you can build more interactive and engaging applications. Jetpack Compose’s declarative approach significantly reduces the complexity of Android UI design, making it a valuable skill for any Android developer looking to streamline their workflow.

MainActivity.kt


package com.cfsuman.jetpackcompose

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Brush
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            GetScaffold()
        }
    }


    @Composable
    fun GetScaffold(){
        Scaffold(
            topBar = {TopAppBar(
                title = {Text(
                    "Compose - Row Background",
                    color = Color.White)},
                backgroundColor = Color(0xFF58427C)) },
            content = {MainContent()},
            backgroundColor = Color(0xFFEDEAE0)
        )
    }


    @Composable
    fun MainContent(){
        Column(
            modifier = Modifier
                .fillMaxSize()
                .padding(8.dp),
            verticalArrangement = Arrangement.SpaceEvenly
        ) {
            Row(
                modifier = Modifier
                    .padding(12.dp)
                    .background(Color(0xFF89CFF0))
                    .fillMaxSize()
                    .weight(1f)
                    .wrapContentSize(align = Alignment.Center)
            ) {
                Text(
                    text = "Row Background",
                    style = MaterialTheme.typography.h5
                )
            }

            Row(
                modifier = Modifier
                    .padding(12.dp)
                    .background(
                        Brush.linearGradient(
                            listOf(
                                Color(0xFFFF7E00),
                                Color(0xFF8DB600),
                                Color(0xFF9966CC)
                            )
                        )
                    )
                    .fillMaxSize()
                    .weight(1f)
                    .wrapContentSize(align = Alignment.Center)
            ) {
                Text(
                    text = "Gradient Background",
                    style = MaterialTheme.typography.h5
                )
            }
        }
    }


    @Preview
    @Composable
    fun ComposablePreview(){
        //GetScaffold()
    }
}