我无法运行setfab.setOnClickListener（new View.OnClickListener（），如果我单击自动停止的onlick意向应用程序

Question

2019-11-10 00:11:11.004 20790-20790/com.adworld.admin.forplay E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.adworld.admin.forplay, PID: 20790
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.adworld.admin.forplay/com.adworld.admin.forplay.Main2Activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.floatingactionbutton.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2932)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3010)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1707)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:192)
        at android.app.ActivityThread.main(ActivityThread.java:6758)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:557)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:875)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.floatingactionbutton.FloatingActionButton.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.adworld.admin.forplay.Main2Activity.onCreate(Main2Activity.java:35)
        at android.app.Activity.performCreate(Activity.java:7147)
        at android.app.Activity.performCreate(Activity.java:7138)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1219)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2885)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3010) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1707) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:192) 
        at android.app.ActivityThread.main(ActivityThread.java:6758) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:557) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:875) 

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Answer 1

我认为您的错误是您尝试在findviewbyid中呼叫FloatingActionButton的地方：

 FloatingActionButton fab = findViewById(R.id.nav_controller_view_tag);

检查您的XML文件以确保您输入正确的ID来找到它