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对空对象引用的View.findViewById（int）'

[英]View.findViewById(int)' on a null object reference

原文 2017-04-08 22:03:28 5 1 java/ android/ nullpointerexception/ mysql-connector

I'm new to AndroidStudio, and I'm working on MySQL connection with JDBC lib. 我是AndroidStudio的新手，并且正在使用JDBC lib进行MySQL连接。

I have no error with compiling but when I run my app, I'm getting this error: 我没有编译错误，但是当我运行我的应用程序时，出现此错误：

appname has stopped. appname已停止。

Thank you. 谢谢。

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.root14.yourapp, PID: 6784 java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference at com.example.root14.yourapp.tab1.onCreateView(tab1.java:25) at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801) at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1638) at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679) at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143) at android.support.v4.view.ViewPager.populate(ViewPager.java:1240) at android.support.v4.view.ViewPager.populate E / AndroidRuntime：致命例外：主进程：com.example.root14.yourapp，PID：6784 java.lang.NullPointerException：尝试在其上调用虚拟方法'android.view.View android.view.View.findViewById（int）' android.support.v4.app上com.example.root14.yourapp.tab1.onCreateView（tab1.java:25）处的空对象引用android.support.v4.app处android.support.v4.app.Fragment.performCreateView（Fragment.java:2080） android.support.v4.app上的.FragmentManagerImpl.moveToState（FragmentManager.java:1108）在android.support.v4.app.BackStackRecord.run（BackStackRecord.java:801）处的FragmentManagerImpl.moveToState（FragmentManager.java:1290） android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss（BackStackRecord.java:679）上的android.support.v4.app.FragmentManagerImpl.execSingleAction（FragmentManager.java:1638）在android.support.v4.app.FragmentPagerAdapter.finishUpdate（ android.support.v4.view.ViewPager.populate上的FragmentPagerAdapter.java:143)(android.support.v4.view.ViewPager.populate上的ViewPager.java:1240） (ViewPager.java:1088) at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:700) at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90) at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1364) at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:765) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at andr （ViewPager.java:1088）在android.support.v4.view.ViewPager.onMeasure（ViewPager.java:1614）在android.view.View.measure（View.java:19731）在android.view.ViewGroup.measureChildWithMargins（ android.support.design.widget.CoordinatorLayout.onMeasureChild（CoordinatorLayout.java:700）上的ViewGroup.java:6120）android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild（HeaderScrollingViewBehavior.java:90）上的ViewGroup.java:6120） .widget.AppBarLayout $ ScrollingViewBehavior.onMeasureChild（AppBarLayout.java:1364）在android.support.design.widget.CoordinatorLayout.onMeasure（CoordinatorLayout.java:765）在android.view.View.measure（View.java:19731）在安卓系统中的android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）android.widget.FrameLayout.onMeasure（FrameLayout.java:185）android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:135） Android上的.view.View.measure（View.java:19731）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120） oid.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) at android.widget.LinearLayout.measureVertical(LinearLayout.java:758) at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) at android.widget.LinearLayout.measureVertical(LinearLayout.java:758) at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) at android.view.View.measure(View.java:19731) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at com.android.internal.policy.DecorView.onMeasure(DecorView.java:687) at android.view.View.measure(View oid.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1464）at android.widget.LinearLayout.measureVertical（LinearLayout.java:758）at android.widget.LinearLayout.onMeasure（LinearLayout.java:640）at android.view.View android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）在android.widget.FrameLayout.onMeasure（FrameLayout.java:185）在android.view.View.measure（View.View.java.19731） java：19731）位于android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）位于android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1464）位于android.widget.LinearLayout.measureVertical（LinearLayout.java:758） android.widget.FrameLayout上的android.widget.LinearLayout.onMeasure（LinearLayout.java:640）在android.view.View.measure（View.java:19731）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）在android.widget.FrameLayout .onMeasure（FrameLayout.java:185）在com.android.internal.policy.DecorView.onMeasure（DecorView.java:687）在android.view.View.measure（查看 .java:19731) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2271) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1358) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1607) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1246) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6301) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:871) at android.view.Choreographer.doCallbacks(Choreographer.java:683) at android.view.Choreographer.doFrame(Choreographer.java:619) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:857) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6077) at java.lang.reflect.Method.invoke(Native Method) 04-08 22:01:09.999 6784-6784/com.example.root14.yourapp E/AndroidRuntime: at com.android. .java：19731，位于android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2271），位于android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1358），位于android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1607）在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1246）在android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:6301）在android.view.Choreographer $ CallbackRecord.run（Choreographer.java:871）在android.view.Choreographer.doCallbacks（Choreographer.java:683）在android.view.Choreographer.doFrame（Choreographer.java:619）在android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:857）在android.os .Handler.handleCallback（Handler.java:751）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:154）在android.app.ActivityThread.main（ ActivityThread.java:6077），位于java.lang.reflect.Method.invoke（本机方法）04-08 22：01：09.999 6784-6784 / com.example.root14.yourapp E / AndroidRuntime：位于com.android。 internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:865）位于com.android.internal.os.ZygoteInit.main（ZygoteInit.java:755）

1 个解决方案

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“ android.view.View android.view.View.findViewById（int）”

Did you tried to debug and check the app for above Null pointer exception? 您是否尝试调试并检查应用程序是否存在上述Null指针异常？

It seems code is trying to access element which is not present in the content_main.xml or activity_main.xml. 似乎代码正在尝试访问content_main.xml或activity_main.xml中不存在的元素。 Hope this helps. 希望这可以帮助。