Scrollable Modifier Monitored By an Offset Value in Android using Jetpack Compose
In Android, a Scrollable modifier detects the scroll gestures, and calculates the scroll offset value, but does not offset its contents. In simpler words, the Scroll Modifier will calculate the amount of scroll performed in a particular orientation (vertical or horizontal), but will actually not displace the view or the element in either scroll direction. We can assume the example of a computer mouse, where the mouse moves over the screen as well as on the trackpad but the trackpad does not change its position. Common applications can be volume bar and screen brightness bar.
In this article, we will show you how you could create a Scrollable Modifier and monitor it in Android using Jetpack Compose. Follow the below steps once the IDE is ready.
Step by Step Implementation
Step 1: Create a New Project in Android Studio
To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. While choosing the template, select Empty Compose Activity. If you do not find this template, try upgrading the Android Studio to the latest version. We demonstrated the application in Kotlin, so make sure you select Kotlin as the primary language while creating a New Project.
Step 2: Working with the MainActivity.kt file
Go to the MainActivity.kt file and refer to the following code. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.
Kotlin
package com.w3wiki.jcscrollablemodifier import android.os.Bundle import androidx.activity.ComponentActivity import androidx.activity.compose.setContent import androidx.compose.foundation.background import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.rememberScrollableState import androidx.compose.foundation.gestures.scrollable import androidx.compose.foundation.layout.* import androidx.compose.material.* import androidx.compose.runtime.getValue import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.runtime.setValue import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.graphics.Color import androidx.compose.ui.unit.dp class MainActivity : ComponentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) setContent { // Creating a Simple Scaffold // Layout for the application Scaffold( // Creating a Top Bar topBar = { TopAppBar(title = { Text( "GFG | Scrollable Modifier" , color = Color.White) }, backgroundColor = Color( 0xff0f9d58 )) }, // Creating Content content = { // Creating a Column Layout Column(Modifier.fillMaxSize(), horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center) { // actual composable state var offset by remember { mutableStateOf(0f) } Box( Modifier .size( 150 .dp) .scrollable( orientation = Orientation.Vertical, // Scrollable state: describes how to consume // scrolling delta and update offset state = rememberScrollableState { delta -> offset += delta delta } ) .background(Color.LightGray), contentAlignment = Alignment.Center ) { Text(offset.toString()) } } } ) } } } |
Output:
You can see that we are able to create a Scrollable Modifier and monitor its offset value.