Java 从活动启动片段活动会导致NullPointerException

我正在尝试向我的项目应用程序的仪表板添加片段。然而，我得到了nullpointerexception 在bottomMenu函数的.setOnItemSelectedListener中，代码如下：

Dashboard.java

}

日志：

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起初，我认为问题是因为我在片段中存储了一个空值，如果是这样的话，那么我该如何修复它，我是新手，所以请让我知道我在这里做错了什么。

您的

chipNavigationBar

变量为空，因此OnItemSelectedListener被实例化为空，这是不可能的

您试图在仪表板中找到chipNavigationBar，但您甚至还没有设置

setContentView（R.layout.yourLayout），这意味着无法找到ViewById

你必须在你的片段中重新设置变量，在那里你有一个有效的视图

chipNavigationBar = findViewById(R.id.bottom_nav_menu);

你忘了设置ContentView，兄弟
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.desikhao, PID: 11751
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.desikhao/com.example.desikhao.LocationOwner.Dashboard}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.ismaeldivita.chipnavigation.ChipNavigationBar.setOnItemSelectedListener(com.ismaeldivita.chipnavigation.ChipNavigationBar$OnItemSelectedListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3308)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3457)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2044)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:224)
    at android.app.ActivityThread.main(ActivityThread.java:7562)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.ismaeldivita.chipnavigation.ChipNavigationBar.setOnItemSelectedListener(com.ismaeldivita.chipnavigation.ChipNavigationBar$OnItemSelectedListener)' on a null object reference
    at com.example.desikhao.LocationOwner.Dashboard.bottomMenu(Dashboard.java:39)
    at com.example.desikhao.LocationOwner.Dashboard.onCreate(Dashboard.java:33)
    at android.app.Activity.performCreate(Activity.java:7893)
    at android.app.Activity.performCreate(Activity.java:7880)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3283)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3457) 
    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$H.handleMessage(ActivityThread.java:2044) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:224) 
    at android.app.ActivityThread.main(ActivityThread.java:7562) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950) 

chipNavigationBar = findViewById(R.id.bottom_nav_menu);