在 Android Studio 中将底部导航栏与其他代码合并

Question

I'm building an app with multiple people right now and I'm trying to merge the bottom navigation bar I made with someone else's code - but the app crashes immediately due to a runtime error after I implemented my navigation bar with this really long message. Anyone know how to fix this?

2020-06-30 00:59:26.429 7505-7505/com.example.unieats E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.unieats, PID: 7505
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.unieats/com.example.unieats.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:3430)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3614)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:86)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2199)
        at android.os.Handler.dispatchMessage(Handler.java:112)
        at android.os.Looper.loop(Looper.java:216)
        at android.app.ActivityThread.main(ActivityThread.java:7625)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)
     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 androidx.navigation.ui.ActivityKt.setupActionBarWithNavController(Activity.kt:74)
        at com.example.unieats.MainActivity.onCreate(MainActivity.kt:27)
        at android.app.Activity.performCreate(Activity.java:7458)
        at android.app.Activity.performCreate(Activity.java:7448)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1286)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3409)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3614) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:86) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2199) 
        at android.os.Handler.dispatchMessage(Handler.java:112) 
        at android.os.Looper.loop(Looper.java:216) 
        at android.app.ActivityThread.main(ActivityThread.java:7625) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987) 

Update: it seems like my MainActivity file is the one causing the problems. Below this is the code for that file - everything before val navView is code that already existed, and everything after is what I added.

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment)
        val appBarConfiguration = AppBarConfiguration(setOf(
            R.id.navigation_home, R.id.navigation_search, R.id.navigation_log,
            R.id.navigation_settings, R.id.navigation_profile))
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController) 
         
    }
}

Answer 1

Can you share the code before before val navView i think there is something wrong there or check your AppTheme in your res/values/style.xml if your AppTheme parent ends with.NoActionBar if so change it to.DarkActionBar Hope it helps

Answer 2

The error doesn't seem to be coming from the navigation bar that you are merging, but instead from the ActionBar. Make sure you have the action bar you are calling in the activity/fragment created so that you can set the title to it, as the error indicates.