nullpointerexception

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 14 days ago . I'm getting the NullPointerException described in the title, but I don't understand how to use the information in the error message to debug it. How do I know what's null, and what are common causes of that? If you're seeing an error like java.lang.NullPointerException: Attempt to invoke virtual method '...' on a null object reference , this question aims to help

问题 This question already has answers here : What is a NullPointerException, and how do I fix it? (12 answers) Closed 14 days ago . I'm getting the NullPointerException described in the title, but I don't understand how to use the information in the error message to debug it. How do I know what's null, and what are common causes of that? If you're seeing an error like java.lang.NullPointerException: Attempt to invoke virtual method '...' on a null object reference , this question aims to help

问题 My Main Activity. This is where all my coding is done. FrameLayout simpleFrameLayout; TabLayout tabLayout; VideoView video; Button btn_show; InterstitialAd interstitialAd; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); btn_show = (Button) findViewById(R.id.bt_show); interstitialAd = new InterstitialAd(this); interstitialAd.setAdUnitId("ca-app-pub-8708219564656739/2401085524"); interstitialAd.loadAd(new

问题 When i created TextClock widget in layout Android Studio layout preview cahsed and didn't show the changes. But on debug devise widget work perfectly. If I commented it layout preview work successfuly. Another PC Android Studio work successfuly and show TextClock. Error Layout preview java.lang.NullPointerException at android.content.ContentResolver.registerContentObserver(ContentResolver.java:2263) at android.widget.TextClock.registerObserver(TextClock.java:626) at android.widget.TextClock

问题 I need to iterate through all the RadioGroups in my RecyclerView . Code i tried: for(int i=0;i<recyclerView.getAdapter().getItemCount();i++) { radioGroup = recyclerView.findViewHolderForAdapterPosition(i).itemView.findViewById(R.id.radio_group); } but findViewHolderForAdapterPosition(i) returns null for RadioGroups that are off screen and gives me a NullPointerException . How do i iterate through all of them? 回答1: RecyclerView views are created/destroyed as needed when you scroll. You cannot

问题 I added a Bottom Navigation Activity to my project but when i start the relevant activity it gives out a Null Pointer Exception. It says that the exception is fired at line number 28 at lk.apiit.eea.mobile.Activities.CompanyProfile.onCreate(CompanyProfile.java:28) 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

问题 This question's answers are a community effort . Edit existing answers to improve this post. It is not currently accepting new answers or interactions. What are Null Pointer Exceptions ( java.lang.NullPointerException ) and what causes them? What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely? 回答1: When you declare a reference variable (i.e. an object) you are really creating a pointer to an object. Consider

问题 I am getting an error message in the LogCat window of Android Studio; Process: com.riverstonetech.gositeuk, PID: 27370 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.riverstonetech.gositeuk/com.riverstonetech.gositeuk.CountriesActivity}: 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

问题 I am getting an error message in the LogCat window of Android Studio; Process: com.riverstonetech.gositeuk, PID: 27370 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.riverstonetech.gositeuk/com.riverstonetech.gositeuk.CountriesActivity}: 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

问题 When I code I am frustrated with null checks. Especially while coding data structures! I have to do it as String val; if(a != null && a.child != null) val = a.child.getValue(); else val = null; Something sort of this... Is there a operator like ?. (which is a part of C#) for Java to shorten the burden ? С# example: String val = a?.child?.getValue(); 回答1: There is no ?. operator in Java, so, as Hari notes, you have to do things the "long winded" way. However, one could argue that this is a