Why does my android application keep stopping?

Question

This application only has front end work. I worked really hard on it but on running it keeps stopping. Here is the stacktrace

2021-05-26 07:13:37.288 3836-3836/? I/le.instagramap: Late-enabling -Xcheck:jni
2021-05-26 07:13:37.337 3836-3836/? E/le.instagramap: Unknown bits set in runtime_flags: 0x8000
2021-05-26 07:13:37.384 3836-3836/? D/ActivityThread: setConscryptValidator
2021-05-26 07:13:37.384 3836-3836/? D/ActivityThread: setConscryptValidator - put
2021-05-26 07:13:37.859 3836-3836/com.example.instagramapp I/Perf: Connecting to perf service.
2021-05-26 07:13:38.427 3836-3836/com.example.instagramapp D/PhoneWindow: forceLight changed to true [] from com.android.internal.policy.PhoneWindow.updateForceLightNavigationBar:4238 com.android.internal.policy.DecorView.updateColorViews:1510 com.android.internal.policy.PhoneWindow.dispatchWindowAttributesChanged:3216 android.view.Window.setFlags:1148 com.android.internal.policy.PhoneWindow.generateLayout:2444 
2021-05-26 07:13:38.429 3836-3836/com.example.instagramapp I/MultiWindowDecorSupport: updateCaptionType >> DecorView@3d08565[], isFloating: false, isApplication: true, hasWindowDecorCaption: false, hasWindowControllerCallback: true
2021-05-26 07:13:38.429 3836-3836/com.example.instagramapp D/MultiWindowDecorSupport: setCaptionType = 0, DecorView = DecorView@3d08565[]
2021-05-26 07:13:38.449 3836-3836/com.example.instagramapp W/le.instagramap: Accessing hidden method Landroid/view/View;->computeFitSystemWindows(Landroid/graphics/Rect;Landroid/graphics/Rect;)Z (greylist, reflection, allowed)
2021-05-26 07:13:38.450 3836-3836/com.example.instagramapp W/le.instagramap: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (greylist, reflection, allowed)
2021-05-26 07:13:38.465 3836-3836/com.example.instagramapp D/AndroidRuntime: Shutting down VM
2021-05-26 07:13:38.468 3836-3836/com.example.instagramapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.instagramapp, PID: 3836
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.instagramapp/com.example.instagramapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3556)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3703)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2216)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7948)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at androidx.navigation.ui.ActionBarOnDestinationChangedListener.setTitle(ActionBarOnDestinationChangedListener.java:48)
        at androidx.navigation.ui.AbstractAppBarOnDestinationChangedListener.onDestinationChanged(AbstractAppBarOnDestinationChangedListener.java:103)
        at androidx.navigation.NavController.addOnDestinationChangedListener(NavController.java:233)
        at androidx.navigation.ui.NavigationUI.setupActionBarWithNavController(NavigationUI.java:227)
        at com.example.instagramapp.MainActivity.onCreate(MainActivity.java:36)
        at android.app.Activity.performCreate(Activity.java:7955)
        at android.app.Activity.performCreate(Activity.java:7944)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3531)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3703) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2216) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:7948) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075) 

Kindly help me resolve the issue. I have recently started android development so sorry if this question does not pass the site's standards.

Answer 1

You should be calling getSupportActionBar().

Here is a reference article:

Android Error [Attempt to invoke virtual method 'void android.app.ActionBar' on a null object reference]

I've also recently got into Android development and as a heads up, if your emulator starts to have issues, make sure you wipe its data. Go to AKD manager, click the arrow to the far right, and select wipe data.