How to Implement Press Back Again to Exit in Android using Jetpack Compose?
The back button is used in many android applications. It is generally used to navigate to the previous page or simply exit the application. Many applications nowadays ask users to press the back button twice to exit the application. In this article, we will be building a simple application in which we will implement press back again to exit the android application using Jetpack Compose.
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: Adding a new color to the Color.kt file
Navigate to app > java > your app’s package name > ui.theme > Color.kt file and add the below code to it.
Kotlin
import androidx.compose.ui.graphics.Color val Purple200 = Color( 0xFF0F9D58 ) val Purple500 = Color( 0xFF0F9D58 ) val Purple700 = Color( 0xFF3700B3 ) val Teal200 = Color( 0xFF03DAC5 ) // on below line we are adding different colors. val greenColor = Color( 0xFF0F9D58 ) |
Step 3: Working with MainActivity.kt file.
Navigate to app>java>your app’s package name>MainActivity.kt file and add the below code to it. Comments are added in the code to get to know in detail.
Kotlin
import android.app.Activity import android.os.Build import android.os.Bundle import android.widget.Toast import androidx.activity.ComponentActivity import androidx.activity.compose.setContent import androidx.annotation.RequiresApi import androidx.compose.foundation.layout.* import androidx.compose.material.* import androidx.compose.runtime.Composable import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.graphics.Color import androidx.compose.ui.platform.LocalContext import androidx.compose.ui.text.font.FontWeight import androidx.compose.ui.text.style.TextAlign import androidx.compose.ui.unit.dp import androidx.compose.ui.unit.sp import com.example.newcanaryproject.ui.theme.NewCanaryProjectTheme import com.example.newcanaryproject.ui.theme.greenColor class MainActivity : ComponentActivity() { @RequiresApi (Build.VERSION_CODES.M) private var pressedTime: Long = 0 override fun onCreate(savedInstanceState: Bundle?) { super .onCreate(savedInstanceState) setContent { NewCanaryProjectTheme { // on below line we are specifying background color for our application Surface( // on below line we are specifying modifier and color for our app modifier = Modifier.fillMaxSize(), color = MaterialTheme.colors.background ) { // on the below line we are specifying the theme as the scaffold. Scaffold( // in scaffold we are specifying the top bar. topBar = { // inside top bar we are specifying background color. TopAppBar(backgroundColor = greenColor, // along with that we are specifying title for our top bar. title = { // in the top bar we are specifying tile as a text Text( // on below line we are specifying // text to display in top app bar. text = "GFG" , // on below line we are specifying // modifier to fill max width. modifier = Modifier.fillMaxWidth(), // on below line we are specifying // text alignment. textAlign = TextAlign.Center, // on below line we are specifying // color for our text. color = Color.White ) }) }) { // on below line we are calling connection information method to display UI pressBackAgainToExit() } } } } } // on below line we are calling on back press method. @RequiresApi (Build.VERSION_CODES.M) override fun onBackPressed() { // on below line we are checking if the press time is greater than 2 sec if (pressedTime + 2000 > System.currentTimeMillis()) { // if time is greater than 2 sec we are closing the application. super .onBackPressed() finish() } else { // in else condition displaying a toast message. Toast.makeText(getBaseContext(), "Press back again to exit" , Toast.LENGTH_SHORT).show(); } // on below line initializing our press time variable pressedTime = System.currentTimeMillis(); } } // on below line we are creating contact picker function. @Composable fun pressBackAgainToExit() { // on below line we are creating variable for activity. val activity = LocalContext.current as Activity // on below line we are creating a column, Column( // on below line we are adding a modifier to it, modifier = Modifier .fillMaxSize() // on below line we are adding a padding. .padding(all = 30 .dp), horizontalAlignment = Alignment.CenterHorizontally, verticalArrangement = Arrangement.Center, ) { // on below line we are adding a text for heading. Text( // on below line we are specifying text text = "Press Back Again to Exit in Android" , // on below line we are specifying text color, font size and font weight color = greenColor, fontSize = 20 .sp, fontWeight = FontWeight.Bold ) } } |