NullPointerException at android.widget.AbsListView.obtainView at android.widget.GridView.onMeasure

本文记录了一次在为GridView设置数据时遇到的空指针异常问题。异常发生在adapter的getView()方法中返回了null值,导致整个应用崩溃。通过本文可以了解到具体的错误信息及解决方法。

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今天给GridView设置数据时一直莫名报空指针,错误信息如下,后来网上搜索查下,才知道知己在adapter的getView()方法里返回的是null,真想给自己一个大嘴巴子,特此记录下这个失误。

 

11-26 16:48:33.209: E/AndroidRuntime(3169): FATAL EXCEPTION: main
11-26 16:48:33.209: E/AndroidRuntime(3169): java.lang.NullPointerException
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.AbsListView.obtainView(AbsListView.java:2269)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.GridView.onMeasure(GridView.java:1030)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:617)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:399)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:617)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:399)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:617)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:399)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1390)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.View.measure(View.java:15172)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:736)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.Choreographer.doCallbacks(Choreographer.java:566)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.Choreographer.doFrame(Choreographer.java:536)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:722)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.os.Handler.handleCallback(Handler.java:615)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.os.Handler.dispatchMessage(Handler.java:92)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.os.Looper.loop(Looper.java:137)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at android.app.ActivityThread.main(ActivityThread.java:4745)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at java.lang.reflect.Method.invokeNative(Native Method)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at java.lang.reflect.Method.invoke(Method.java:511)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-26 16:48:33.209: E/AndroidRuntime(3169):  at dalvik.system.NativeStart.main(Native Method)

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.hjschoolhelper210301201_1, PID: 13135 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at com.example.hjschoolhelper210301201_1.ClubinfoAdpter.getView(ClubinfoAdpter.java:44) at android.widget.AbsListView.obtainView(AbsListView.java:2458) at android.widget.ListView.makeAndAddView(ListView.java:2067) at android.widget.ListView.fillDown(ListView.java:793) at android.widget.ListView.fillFromTop(ListView.java:855) at android.widget.ListView.layoutChildren(ListView.java:1838) at android.widget.AbsListView.onLayout(AbsListView.java:2255) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1855) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332) at android.widget.FrameLayout.onLayout(FrameLayout.java:270) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:536) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332) at android.widget.FrameLayout.onLayout(FrameLayout.java:270) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1891) at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1729) at android.widget.LinearLayout.onLayout(LinearLayout.java:1638) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332) at android.widget.FrameLayout.onLayout(FrameLayout.java:270) at com.android.internal.policy.DecorView.onLayout(DecorView.java:799) at android.view.View.layout(View.java:23693) at android.view.ViewGroup.layout(ViewGroup.java:6413) at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3999) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:3372) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:2328) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:9087) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1231) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:1239) at android.view.Choreographer.doCallbacks(Choreographer.java:899) at android.view.Choreographer.doFrame(Choreographer.java:832) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:1214) at android.os.Handler.handleCallback(Handler.java:942) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loopOnce(Looper.java:201) at android.os.Looper.loop(Looper.java:288) at android.app.ActivityThread.main(ActivityThread.java:7872) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)
05-17
<think>嗯,用户遇到了一个Java中的NullPointerException异常,具体是在调用android.view.View.getVisibility方法时出现的。错误信息是“java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.View.getVisibility()' on a null object reference”。我需要帮他分析这个问题,并提供解决方案。 首先,我应该回忆一下NullPointerException的一般原因。通常,这种异常是因为调用了某个对象的方法,但该对象实际上为null。所以这里的问题可能在于,尝试调用getVisibility()的那个View对象是空的,没有被正确初始化或者已经被销毁了。 接下来,我需要考虑在Android开发中,哪些情况会导致View对象为null。常见的情况包括:在findViewById时没有找到对应的视图,导致返回null;或者在Fragment中,视图还没有被inflate完成,就尝试访问其中的View组件;还有可能在Adapter的getView方法中错误地返回了null,或者在视图已经被销毁后仍然尝试访问它,比如在Activity的onDestroy之后调用了某些方法。 然后,我应该分步骤分析解决方法。第一步肯定是定位问题发生的具体位置,查看堆栈跟踪,找到抛出异常的代码行。用户需要检查那行代码中的View对象是否被正确初始化。例如,是否在setContentView之后调用findViewById,或者在Fragment的onCreateView之后才访问视图组件。 第二步是检查View的初始化过程。比如,在Activity中,是否在setContentView之后才调用findViewById?在Fragment中,是否在onCreateView中正确inflate了布局,并且只在onViewCreated之后访问视图?另外,动态添加的View是否被正确添加到布局中? 第三步是考虑生命周期的问题。比如,是否在Activity的onDestroy之后或者Fragment的onDetach之后仍然尝试访问View?这时候View可能已经被销毁,再次访问就会导致空指针。需要确保在适当的生命周期方法中处理View的引用,避免在视图不可用时进行操作。 第四步是检查Adapter的情况,特别是自定义Adapter中getView方法是否正确返回了非空的View对象。如果getView返回了null,会导致ListView或RecyclerView在渲染时抛出异常。需要确保getView方法总是返回有效的视图,或者检查是否有条件分支导致返回了null。 另外,可能还需要检查是否有异步任务或者回调函数在视图销毁后仍然试图更新UI。比如,网络请求返回后,如果Activity已经结束,而回调中仍然调用view.setVisibility(),就会引发这个问题。这时候需要取消异步任务或者在回调中检查视图是否仍然有效。 还可以建议用户使用空安全操作符,比如在Kotlin中使用安全调用?.,或者在Java中进行空判断,先检查view != null再调用其方法。此外,使用@Nullable和@NonNull注解可以帮助静态分析工具检测潜在的空指针问题。 最后,提醒用户使用Android Studio的调试工具,比如断点调试或者在Logcat中查看详细的堆栈信息,帮助定位问题。还可以建议单元测试或自动化测试来捕捉这类异常。 总结下来,解决方案应该包括:检查View的初始化、确保生命周期正确管理、验证Adapter返回的View非空、处理异步回调中的空指针情况,以及使用工具进行调试和测试。</think>### 解决方案:`java.lang.NullPointerException`(调用`View.getVisibility()`时空指针异常) #### 问题根源 此异常表明代码中尝试调用`view.getVisibility()`时,`view`对象未被正确初始化或已被销毁,导致其值为`null`[^4][^2]。 --- ### 分步排查与解决 #### 1. **定位异常位置** - **查看堆栈跟踪**:找到报错的具体代码行(如`MainActivity.java:42`),定位到涉及`view.getVisibility()`的调用位置。 - **示例代码**: ```java View myView = findViewById(R.id.my_view); int visibility = myView.getVisibility(); // 若myView未正确初始化,此处报错 ``` #### 2. **检查View初始化** - **场景1:Activity/Fragment中未正确绑定视图** - **错误示例**: ```java public class MainActivity extends Activity { private View myView; // 未初始化 public void onCreate(Bundle savedInstanceState) { setContentView(R.layout.activity_main); myView.getVisibility(); // myView为null } } ``` - **修复方法**: ```java public class MainActivity extends Activity { private View myView; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); myView = findViewById(R.id.my_view); // 必须初始化 myView.getVisibility(); } } ``` - **场景2:Fragment中过早访问视图** - **正确做法**:在`onViewCreated()`中操作视图: ```java public class MyFragment extends Fragment { private View myView; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { return inflater.inflate(R.layout.fragment_layout, container, false); } @Override public void onViewCreated(View view, Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); myView = view.findViewById(R.id.my_view); // 此时视图已初始化 myView.getVisibility(); } } ``` #### 3. **验证生命周期状态** - **避免在销毁后操作视图**: ```java public class MainActivity extends Activity { private View myView; @Override protected void onDestroy() { super.onDestroy(); myView = null; // 释放引用 } // 其他方法中需检查myView是否为null private void updateView() { if (myView != null) { myView.getVisibility(); } } } ``` #### 4. **检查Adapter中的空返回** - **自定义Adapter示例**: ```java public class MyAdapter extends BaseAdapter { @Override public View getView(int position, View convertView, ViewGroup parent) { if (convertView == null) { convertView = LayoutInflater.from(parent.getContext()) .inflate(R.layout.item_layout, parent, false); } // 必须确保返回的convertView非空 return convertView; // 若此处返回null,会导致异常 } } ``` #### 5. **异步任务中的空检查** - **示例(网络请求回调)**: ```java public void fetchData() { ApiClient.getData(new Callback() { @Override public void onResponse(Response response) { if (myView != null && !isFinishing()) { // 检查Activity是否存活 myView.setVisibility(View.VISIBLE); } } }); } ``` --- ### 工具辅助 1. **启用`StrictMode`**:检测线程问题导致的视图操作。 2. **使用`@Nullable`/`@NonNull`注解**: ```java public void setViewVisibility(@NonNull View view) { view.getVisibility(); // 编译器会提示非空 } ``` --- ### 总结流程图 ``` 定位异常代码行 → 检查View初始化 → 验证生命周期 → 检查Adapter返回值 → 异步任务空检查 ``` ---
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