I am developing an Android app using Kotlin. I am trying to understand how Dagger 2 works to perform dependency injection. I am very new to Dagger 2. I am following this tutorial,https://medium.com/@elye.project/dagger-2-for-dummies-in-kotlin-with-one-page-simple-code-project-618a5f9f2fe8 to understand how it works and applying it to my project too. But I am getting an error. Following is what I have done so far.
I created an interface called AppComponent with the following code
package com.example.utils
import com.example.memento.LoginActivity
import dagger.Component
@Component
interface AppComponent
{
fun inject(app: LoginActivity)
}
I also created a class called AuthService with the following code.
package com.example.services
import javax.inject.Inject
class AuthService @Inject constructor()
{
public fun login(): String
{
return "I am logged in";
}
}
This is my LoginActivity class
class LoginActivity : AppCompatActivity()
{
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
val authService = DaggerAppComponent.create().inject(this) as AuthService
tv_testing.text = authService.login();
}
}
When I run my app, I get the following error
java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at com.example.memento.LoginActivity.onCreate(LoginActivity.kt:25)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at androidx.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:674)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
E/MonitoringInstr: Exception encountered by: com.example.memento.LoginActivity@39cc00e. Dumping thread state to outputs and pining for the fjords.
java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at com.example.memento.LoginActivity.onCreate(LoginActivity.kt:25)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at androidx.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:674)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
E/THREAD_STATE: Thread[MonitoringInstrumentation,5,main]
java.lang.Object.wait(Native Method)
android.app.Instrumentation.startActivitySync(Instrumentation.java:496)
android.app.Instrumentation.startActivitySync(Instrumentation.java:435)
androidx.test.runner.MonitoringInstrumentation.access$101(MonitoringInstrumentation.java:98)
androidx.test.runner.MonitoringInstrumentation$4.call(MonitoringInstrumentation.java:443)
androidx.test.runner.MonitoringInstrumentation$4.call(MonitoringInstrumentation.java:440)
java.util.concurrent.FutureTask.run(FutureTask.java:266)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
java.lang.Thread.run(Thread.java:764)
Thread[Binder:11719_2,5,main]
Thread[magnifier pixel copy result handler,5,main]
android.os.MessageQueue.nativePollOnce(Native Method)
android.os.MessageQueue.next(MessageQueue.java:326)
android.os.Looper.loop(Looper.java:160)
android.os.HandlerThread.run(HandlerThread.java:65)
Thread[FinalizerWatchdogDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Daemons$FinalizerWatchdogDaemon.sleepUntilNeeded(Daemons.java:297)
java.lang.Daemons$FinalizerWatchdogDaemon.runInternal(Daemons.java:277)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[InstrumentationConnectionThread,5,main]
android.os.MessageQueue.nativePollOnce(Native Method)
android.os.MessageQueue.next(MessageQueue.java:326)
android.os.Looper.loop(Looper.java:160)
android.os.HandlerThread.run(HandlerThread.java:65)
Thread[Profile Saver,5,system]
Thread[main,5,main]
dalvik.system.VMStack.getThreadStackTrace(Native Method)
java.lang.Thread.getStackTrace(Thread.java:1538)
java.lang.Thread.getAllStackTraces(Thread.java:1588)
androidx.test.runner.MonitoringInstrumentation.getThreadState(MonitoringInstrumentation.java:643)
androidx.test.runner.MonitoringInstrumentation.dumpThreadStateToOutputs(MonitoringInstrumentation.java:638)
androidx.test.runner.MonitoringInstrumentation.onException(MonitoringInstrumentation.java:632)
androidx.test.runner.AndroidJUnitRunner.onException(AndroidJUnitRunner.java:522)
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2910)
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
android.os.Handler.dispatchMessage(Handler.java:106)
android.os.Looper.loop(Looper.java:193)
android.app.ActivityThread.main(ActivityThread.java:6669)
java.lang.reflect.Method.invoke(Native Method)
com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Thread[Binder:11719_1,5,main]
Thread[ReferenceQueueDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Daemons$ReferenceQueueDaemon.runInternal(Daemons.java:178)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[Jit thread pool worker thread 0,5,main]
Thread[FinalizerDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Object.wait(Object.java:422)
java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:188)
java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:209)
java.lang.Daemons$FinalizerDaemon.runInternal(Daemons.java:232)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[HeapTaskDaemon,5,system]
Thread[Instr: com.example.memento.MockTestRunner,5,main]
java.lang.Object.w
E/MonitoringInstr: Dying now...
D/AndroidRuntime: Shutting down VM
--------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.memento, PID: 11719
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.memento/com.example.memento.LoginActivity}: java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at com.example.memento.LoginActivity.onCreate(LoginActivity.kt:25)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at androidx.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:674)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
E/MonitoringInstr: Exception encountered by: Thread[main,5,main]. Dumping thread state to outputs and pining for the fjords.
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.memento/com.example.memento.LoginActivity}: java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.ClassCastException: kotlin.Unit cannot be cast to com.example.services.AuthService
at com.example.memento.LoginActivity.onCreate(LoginActivity.kt:25)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at androidx.test.runner.MonitoringInstrumentation.callActivityOnCreate(MonitoringInstrumentation.java:674)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
E/THREAD_STATE: Thread[MonitoringInstrumentation,5,main]
java.lang.Object.wait(Native Method)
android.app.Instrumentation.startActivitySync(Instrumentation.java:496)
android.app.Instrumentation.startActivitySync(Instrumentation.java:435)
androidx.test.runner.MonitoringInstrumentation.access$101(MonitoringInstrumentation.java:98)
androidx.test.runner.MonitoringInstrumentation$4.call(MonitoringInstrumentation.java:443)
androidx.test.runner.MonitoringInstrumentation$4.call(MonitoringInstrumentation.java:440)
java.util.concurrent.FutureTask.run(FutureTask.java:266)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
java.lang.Thread.run(Thread.java:764)
Thread[Binder:11719_2,5,main]
Thread[magnifier pixel copy result handler,5,main]
android.os.MessageQueue.nativePollOnce(Native Method)
android.os.MessageQueue.next(MessageQueue.java:326)
android.os.Looper.loop(Looper.java:160)
android.os.HandlerThread.run(HandlerThread.java:65)
Thread[FinalizerWatchdogDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Daemons$FinalizerWatchdogDaemon.sleepUntilNeeded(Daemons.java:297)
java.lang.Daemons$FinalizerWatchdogDaemon.runInternal(Daemons.java:277)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[InstrumentationConnectionThread,5,main]
android.os.MessageQueue.nativePollOnce(Native Method)
android.os.MessageQueue.next(MessageQueue.java:326)
android.os.Looper.loop(Looper.java:160)
android.os.HandlerThread.run(HandlerThread.java:65)
Thread[Profile Saver,5,system]
Thread[main,5,main]
dalvik.system.VMStack.getThreadStackTrace(Native Method)
java.lang.Thread.getStackTrace(Thread.java:1538)
java.lang.Thread.getAllStackTraces(Thread.java:1588)
androidx.test.runner.MonitoringInstrumentation.getThreadState(MonitoringInstrumentation.java:643)
androidx.test.runner.MonitoringInstrumentation.dumpThreadStateToOutputs(MonitoringInstrumentation.java:638)
androidx.test.runner.MonitoringInstrumentation.onException(MonitoringInstrumentation.java:632)
androidx.test.runner.AndroidJUnitRunner.onException(AndroidJUnitRunner.java:522)
androidx.test.runner.MonitoringInstrumentation$3.uncaughtException(MonitoringInstrumentation.java:268)
java.lang.Thread.dispatchUncaughtException(Thread.java:1955)
Thread[Binder:11719_1,5,main]
Thread[ReferenceQueueDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Daemons$ReferenceQueueDaemon.runInternal(Daemons.java:178)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[Jit thread pool worker thread 0,5,main]
Thread[FinalizerDaemon,5,system]
java.lang.Object.wait(Native Method)
java.lang.Object.wait(Object.java:422)
java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:188)
java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:209)
java.lang.Daemons$FinalizerDaemon.runInternal(Daemons.java:232)
java.lang.Daemons$Daemon.run(Daemons.java:103)
java.lang.Thread.run(Thread.java:764)
Thread[HeapTaskDaemon,5,system]
Thread[Instr: com.example.memento.MockTestRunner,5,main]
java.lang.Object.wait(Native Method)
java.lang.Thread.parkFor$(Thread.java:2137)
sun.misc.Unsafe.park(Unsafe.java:358)
java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:230)
java.util.concurrent.FutureTask.awaitDone(FutureTask.java:447)
java.util.concurrent.FutureTask.get(FutureTask.java:205)
androidx.test.runner.MonitoringInstrumentation.startActivitySync(MonitoringInstrumentation.java:448)
androidx.test.rule.ActivityTestRule.launchActivity(ActivityTestRule.java:354)
androidx.test.rule.ActivityTestRule$ActivityStatement.evaluate(ActivityTestRule.java:525)
org.junit.rules.RunRules.evaluate(RunRules.java:20)
org.junit.runners.ParentRunner.runLeaf(ParentRunner
E/MonitoringInstr: Dying now...
W/MonitoringInstr: Invoking uncaught exception handler java.lang.ThreadGroup[name=main,maxpri=10] (a class java.lang.ThreadGroup)
I/Process: Sending signal. PID: 11719 SIG: 9
Test running failed: Instrumentation run failed due to 'Process crashed.'
What is wrong with my code?
I tried updating the LoginActivity to this
class LoginActivity : AppCompatActivity()
{
lateinit var authService: AuthService
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
DaggerAppComponent.create().inject(this)
tv_testing.text = authService.login()
}
}
Then I got this error
kotlin.UninitializedPropertyAccessException: lateinit property authService has not been initialized
at com.example.memento.LoginActivity.onCreate(LoginActivity.kt:27)
DaggerAppComponent.create().inject(this) doesn't return anything but you're trying to cast it to AuthService. Therefore, you get ClassCastException. Instead, you should first declare AuthService as lateinit var and annotate it with @Inject. Then you can call inject() function. You can see full code below:
class LoginActivity : AppCompatActivity()
{
@Inject
private lateinit var authService: AuthService
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_login)
DaggerAppComponent.create().inject(this)
tv_testing.text = authService.login();
}
}
I hope my answer helps.