Android底部导航活动在onCreate中给出了空指针异常 [英] Android Bottom Navigation Activity gives a Null Pointer Exception in onCreate

问题描述

我在项目中添加了一个底部导航活动，但是当我启动相关活动时，它会给出一个空指针异常。

I added a Bottom Navigation Activity to my project but when i start the relevant activity it gives out a Null Pointer Exception.

该异常在以下位置触发行号28

It says that the exception is fired at line number 28

at lk.apiit.eea.mobile.Activities.CompanyProfile.onCreate（CompanyProfile.java:28）

at lk.apiit.eea.mobile.Activities.CompanyProfile.onCreate(CompanyProfile.java:28)

以下是例外，代码
请帮助我解决此问题。.谢谢

Following is the Exception and the Code PLease help me fix this.. Thank you

java.lang.RuntimeException: Unable to start activity ComponentInfo{lk.apiit.eea.mobile/lk.apiit.eea.mobile.Activities.CompanyProfile}: 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:2720)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2781)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1508)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:241)
    at android.app.ActivityThread.main(ActivityThread.java:6274)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
 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:100)
    at androidx.navigation.NavController.addOnDestinationChangedListener(NavController.java:218)
    at androidx.navigation.ui.NavigationUI.setupActionBarWithNavController(NavigationUI.java:220)
    at lk.apiit.eea.mobile.Activities.CompanyProfile.onCreate(CompanyProfile.java:28)
    at android.app.Activity.performCreate(Activity.java:6720)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2673)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2781) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1508) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:241) 
    at android.app.ActivityThread.main(ActivityThread.java:6274) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

这是onCreateMethod中的代码

An this is the code in onCreateMethod

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_company_profile);
    BottomNavigationView navView = findViewById(R.id.nav_view);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
            R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)
            .build();
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
    NavigationUI.setupWithNavController(navView, navController);
}

推荐答案

如果您不打电话 setSupportActionBar（），并且您使用的是 NoActionBar 主题，则没有ActionBar。 setupActionBarWithNavController（）假定您有一个ActionBar，因此假定为NullPointerException。

If you aren't calling setSupportActionBar() and you are using a NoActionBar theme, then you don't have an ActionBar. setupActionBarWithNavController() assumes you have an ActionBar, hence the NullPointerException.

您应该切换到提供ActionBar或在布局中使用工具栏调用 setSupportActionBar（），然后再调用 setupActionBarWithNavController（）。

You should switch to a theme that provides an ActionBar or call setSupportActionBar() with a Toolbar in your layout before calling setupActionBarWithNavController().

这篇关于Android底部导航活动在onCreate中给出了空指针异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！