I got a null pointer exception while playing with navigation in jetpack compose. Dont know exactly why it is giving a null pointer exception. I have two screens Home and Details. This is MainActivity.
package com.example.composenavigation
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.navigation.NavController
import androidx.navigation.NavHostController
import androidx.navigation.compose.rememberNavController
import com.example.composenavigation.ui.theme.ComposeNavigationTheme
class MainActivity : ComponentActivity() {
private lateinit var navController: NavHostController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
ComposeNavigationTheme {
navController = rememberNavController()
SetupNavGraph(navController = navController)
}
}
}
}
This is My Home and Detailed Screen respectively.
package com.example.composenavigation
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.navigation.NavController
import androidx.navigation.compose.rememberNavController
@Composable
fun HomeScreen(
navController: NavController
) {
Box(
modifier = Modifier.fillMaxSize(),
contentAlignment = Alignment.Center
) {
Text(
modifier = Modifier.clickable {
navController.navigate(route = Screen.Detail.route)
},
text = "Home",
color = MaterialTheme.colorScheme.primary,
fontSize = MaterialTheme.typography.displayMedium.fontSize
)
}
}
@Preview(showBackground = true)
@Composable
fun HomeScreenPreview() {
HomeScreen(navController = rememberNavController())
}
package com.example.composenavigation
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Text
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.tooling.preview.Preview
import androidx.navigation.NavController
import androidx.navigation.compose.rememberNavController
@Composable
fun DetailedScreen(
navController: NavController
) {
Box(
modifier = Modifier.fillMaxSize(),
contentAlignment = Alignment.Center
) {
Text(
modifier = Modifier.clickable {
navController.popBackStack()
},
text = "Details",
color = Color.Red,
fontSize = MaterialTheme.typography.displayMedium.fontSize
)
}
}
@Preview(showBackground = true)
@Composable
fun DetailedScreenPreview() {
DetailedScreen(navController = rememberNavController())
}
This is my Screen.kt sealed class.
package com.example.composenavigation
sealed class Screen(val route: String) {
object Home : Screen(route = "home_route")
object Detail : Screen(route = "detail_route")
}
This is my Nav Graph.
package com.example.composenavigation
import androidx.compose.runtime.Composable
import androidx.navigation.NavController
import androidx.navigation.NavHostController
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.rememberNavController
@Composable
fun SetupNavGraph(
navController: NavHostController
) {
NavHost(
navController = navController,
startDestination = Screen.Home.route
) {
composable(
route = Screen.Home.route
) {
HomeScreen(navController = rememberNavController())
}
composable(
route = Screen.Detail.route
) {
DetailedScreen(navController = rememberNavController())
}
}
}
This is my stack trace.
FATAL EXCEPTION: main
Process: com.example.composenavigation, PID: 14947
java.lang.NullPointerException
at androidx.navigation.NavController.navigate(NavController.kt:1612)
at androidx.navigation.NavController.navigate(NavController.kt:1938)
at androidx.navigation.NavController.navigate$default(NavController.kt:1933)
at com.example.composenavigation.HomeScreenKt$HomeScreen$1$1.invoke(HomeScreen.kt:26)
at com.example.composenavigation.HomeScreenKt$HomeScreen$1$1.invoke(HomeScreen.kt:25)
at androidx.compose.foundation.ClickableKt$clickable$4$gesture$1$1$2.invoke-k-4lQ0M(Clickable.kt:167)
at androidx.compose.foundation.ClickableKt$clickable$4$gesture$1$1$2.invoke(Clickable.kt:156)
at androidx.compose.foundation.gestures.TapGestureDetectorKt$detectTapAndPress$2$1$1.invokeSuspend(TapGestureDetector.kt:234)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTaskKt.resume(DispatchedTask.kt:178)
at kotlinx.coroutines.DispatchedTaskKt.dispatch(DispatchedTask.kt:166)
at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:397)
at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl(CancellableContinuationImpl.kt:431)
at kotlinx.coroutines.CancellableContinuationImpl.resumeImpl$default(CancellableContinuationImpl.kt:420)
at kotlinx.coroutines.CancellableContinuationImpl.resumeWith(CancellableContinuationImpl.kt:328)
at androidx.compose.ui.input.pointer.SuspendingPointerInputFilter$PointerEventHandlerCoroutine.offerPointerEvent(SuspendingPointerInputFilter.kt:566)
at androidx.compose.ui.input.pointer.SuspendingPointerInputFilter.dispatchPointerEvent(SuspendingPointerInputFilter.kt:456)
at androidx.compose.ui.input.pointer.SuspendingPointerInputFilter.onPointerEvent-H0pRuoY(SuspendingPointerInputFilter.kt:469)
at androidx.compose.ui.node.BackwardsCompatNode.onPointerEvent-H0pRuoY(BackwardsCompatNode.kt:394)
at androidx.compose.ui.input.pointer.Node.dispatchMainEventPass(HitPathTracker.kt:314)
at androidx.compose.ui.input.pointer.Node.dispatchMainEventPass(HitPathTracker.kt:301)
at androidx.compose.ui.input.pointer.NodeParent.dispatchMainEventPass(HitPathTracker.kt:183)
at androidx.compose.ui.input.pointer.HitPathTracker.dispatchChanges(HitPathTracker.kt:102)
at androidx.compose.ui.input.pointer.PointerInputEventProcessor.process-BIzXfog(PointerInputEventProcessor.kt:98)
at androidx.compose.ui.platform.AndroidComposeView.sendMotionEvent-8iAsVTc(AndroidComposeView.android.kt:1329)
at androidx.compose.ui.platform.AndroidComposeView.handleMotionEvent-8iAsVTc(AndroidComposeView.android.kt:1275)
at androidx.compose.ui.platform.AndroidComposeView.dispatchTouchEvent(AndroidComposeView.android.kt:1214)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3138)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2797)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3138)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2797)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3138)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2797)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3138)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2797)
at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:469)
at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1859)
at android.app.Activity.dispatchTouchEvent(Activity.java:3996)
at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:427)
at android.view.View.dispatchPointerEvent(View.java:13737)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:5691)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:5485)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4984)
2023-02-17 14:41:48.799 AndroidRuntime E at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:5037)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:5003)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:5143)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:5011)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:5200)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4984)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:5037)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:5003)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:5011)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4984)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:7810)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:7779)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:7729)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:7949)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:188)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:336)
at android.os.Looper.loop(Looper.java:215)
at android.app.ActivityThread.main(ActivityThread.java:7593)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:980)
Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [androidx.compose.ui.platform.MotionDurationScaleImpl@e98cd80, androidx.compose.runtime.BroadcastFrameClock@6acafb9, StandaloneCoroutine{Cancelling}@7275ffe, AndroidUiDispatcher@777735f]
What's wrong here?
You have too many navControllers.
You only need one:
setContent {
ComposeNavigationTheme {
navController = rememberNavController() // Leave this one
SetupNavGraph(navController = navController)
}
}
Use an existing controller, don't create new ones:
@Composable
fun SetupNavGraph(
navController: NavHostController
) {
NavHost(
navController = navController,
startDestination = Screen.Home.route
) {
composable(
route = Screen.Home.route
) {
HomeScreen(navController = navController) // Here
}
composable(
route = Screen.Detail.route
) {
DetailedScreen(navController = navController) //And here
}
}
}