View.findViewById（INT）＆＃39;在空对象引用

Question

我是AndroidStudio的新手，我正在使用JDBC lib进行MySQL连接。

编译时没有错误，但是当我运行我的应用时，我收到了这个错误：

  

appname已停止。

谢谢。

  

E / AndroidRuntime：致命异常：主要                                                                                处理：com.example.root14.yourapp，PID：6784                                                                                java.lang.NullPointerException：尝试调用虚方法＆＃39; android.view.View android.view.View.findViewById（int）＆＃39;在null对象引用上                                                                                    在com.example.root14.yourapp.tab1.onCreateView（tab1.java:25）                                                                                    在android.support.v4.app.Fragment.performCreateView（Fragment.java:2080）                                                                                    在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1108）                                                                                    在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1290）                                                                                    在android.support.v4.app.BackStackRecord.run（BackStackRecord.java:801）                                                                                    在android.support.v4.app.FragmentManagerImpl.execSingleAction（FragmentManager.java:1638）                                                                                    在android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss（BackStackRecord.java:679）                                                                                    在android.support.v4.app.FragmentPagerAdapter.finishUpdate（FragmentPagerAdapter.java:143）                                                                                    在android.support.v4.view.ViewPager.populate（ViewPager.java:1240）                                                                                    在android.support.v4.view.ViewPager.populate（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（ViewGroup.java:6120）                                                                                    在android.support.design.widget.CoordinatorLayout.onMeasureChild（CoordinatorLayout.java:700）                                                                                    在android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild（HeaderScrollingViewBehavior.java:90）                                                                                    在android.support.design.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android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）                                                                                    在android.widget.FrameLayout.onMeasure（FrameLayout.java:185）                                                                                    在android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:135）                                                                                    在android.view.View.measure（View.java:19731）                                                                                    在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）                                                                                    在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1464）                                                                                    在android.widget.LinearLayout.measureVertical（LinearLayout.java:758）                                                                                    在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android.view.View.measure（View.java:19731）                                                                                    在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6120）                                                                                    在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1464）                                                                                    在android.widget.LinearLayout.measureVertical（LinearLayout.java:758）                                                                                    在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（View.java:19731）                                                                                    在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2271）                                                                                    在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1358）                                                                                    在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）                                                                                    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.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:865）                                                                                    在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:755）

Answer 1

  

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）'

您是否尝试调试并检查应用程序是否存在上述空指针异常？

似乎代码正在尝试访问content_main.xml或activity_main.xml中不存在的元素。希望这会有所帮助。