android - Android :iam 总是收到这个提示，任何人都可以解决这个问题吗？

Question

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.mcc.wpnews.adapters.MenuCommonAdapter$ViewHolder.<init>(MenuCommonAdapter.java:67)
    at com.mcc.wpnews.adapters.MenuCommonAdapter.onCreateViewHolder(MenuCommonAdapter.java:47)
    at com.mcc.wpnews.adapters.MenuCommonAdapter.onCreateViewHolder(MenuCommonAdapter.java:27)
    at android.support.v7.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:6493)
    at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5680)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5563)
    at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5559)
    at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2229)
    at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1556)
    at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1516)
    at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:608)
    at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3693)
    at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3109)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    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:19886)
    at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1306)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.widget.ScrollView.onMeasure(ScrollView.java:348)
    at android.view.View.measure(View.java:19886)
    at android.support.v4.widget.SwipeRefreshLayout.onMeasure(SwipeRefreshLayout.java:626)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    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:19886)
    at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
    at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    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:19886)
    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1060)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    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:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    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:19886)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6085)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
    at com.android.internal.policy.DecorView.onMeasure(DecorView.java:693)
    at android.view.View.measure(View.java:19886)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2319)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1410)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1663)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1298)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6437)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:876)
    at android.view.Choreographer.doCallbacks(Choreographer.java:688)
    at android.view.Choreographer.doFrame(Choreographer.java:623)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:862)
    at android.os.Handler.handleCallback(Handler.java:754)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:163)
    at android.app.ActivityThread.main(ActivityThread.java:6238)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)

标签： androidonclicklistener

Answer 1

首先，您必须了解什么是 NullPointer 异常。让我尽可能简单地解释一下。

空指针异常： 当您在尚未初始化的变量（视图）上调用方法或函数时，将引发此异常。

在这里，您会收到此错误，因为您可能尚未正确声明并将视图映射到变量名称。

你必须做什么？ 只需检查您是否已声明该视图。在这里，您收到 OnClick 侦听器错误。所以我假设它是按钮。因此，请检查按钮是否存在于 xml 布局中，并且您已在 java 代码中正确声明和初始化。