调用 getActivity().getApplicationContext() 时片段类中的 Nullpointer 异常 [关闭]答案

【问题标题】：Nullpointer exception inside fragment class while calling getActivity().getApplicationContext() [closed]调用 getActivity().getApplicationContext() 时片段类中的 Nullpointer 异常 [关闭]
【发布时间】：2014-11-05 09:49:30
【问题描述】：

我在这里使用光标时遇到空指针异常。我在这一点上感到困惑，因为我相信每个片段都在一个活动中，并且我在谷歌那里引用了一些点，从我得到这个异常发生而我的片段实例不是附加到活动中。（我的程序是从图库中获取所有图像并将其作为网格视图在我的片段中列出，我在这里使用 SWIPABLE 视图）。提前谢谢...

 public ArrayList<String> getFilePaths()
        {

//       android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI
//       android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI
            Uri u =MediaStore.Images.Media.EXTERNAL_CONTENT_URI; 
            System.out.println("uri is"+u);
            String[] projection =  { MediaStore.Images.Media.DATA }; 

//              {MediaStore.Images.ImageColumns.DATA};
//          { MediaStore.Images.Media.DATA };
            Cursor c = null;

            //treeset in which images are sorted in ascending order
            SortedSet<String> dirList = new TreeSet<String>();
            ArrayList<String> resultIAV = new ArrayList<String>();

             String[] directories = null; 
            if ((u != null) &&(projection!=null)) 
            { 
                System.out.println("projection is"+projection);
                //null pointer exception
//               Cursor cursor = getContentResolver().query(selectedImage,
//                       filePathColumn, null, null, null);
                //getContentResolver().
                Log.e("devicetab","cursor not equalto null");
                Log.e("devicetab",getActivity().getApplicationContext().toString());
                //not executing this line
                //getSupportLoadManager().initLoader(0, null, getActivity());
//              c=getSupportLoaderManager.(u, projection,null,null,null); 
                System.out.println("context "+getActivity().getApplicationContext());

                System.out.println("activity"+getActivity());
                c =getActivity().getApplicationContext().getContentResolver().query(u, projection, null, null, null); 
//              c =getActivity().getContentResolver().query(u, projection,null,null,null); 
                getActivity().startManagingCursor(c);
                c.moveToFirst();
                Log.e("devicetab","cursor");

            } 

            if ((c != null) && (c.moveToFirst())) 
            { 
                do 
                {
                    String tempDir = c.getString(0);
                    tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
                    try{
                        dirList.add(tempDir);
                    }
                    catch(Exception e)
                    {

                    }
                } 
                while (c.moveToNext());
                //string array driectories
                directories = new String[dirList.size()];
                dirList.toArray(directories);

            }
//             c.close();
            for(int i=0;i<dirList.size();i++)
            {
                File imageDir = new File(directories[i]);
                File[] imageList = imageDir.listFiles();

//              File targetDirector = new File(picturePath);
//              Log.e("Devicetab","before files");
//              File[] files = targetDirector.listFiles();



                if(imageList == null)
                    continue;
                for (File imagePath : imageList) { 
                    try {

                            if(imagePath.isDirectory())
                            {
                                imageList = imagePath.listFiles();

                            }
                            if ( imagePath.getName().contains(".jpg")|| imagePath.getName().contains(".JPG")  
                                    || imagePath.getName().contains(".jpeg")|| imagePath.getName().contains(".JPEG")                                    
                                    || imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
                                    || imagePath.getName().contains(".gif") || imagePath.getName().contains(".GIF")
                                    || imagePath.getName().contains(".bmp") || imagePath.getName().contains(".BMP")                         
            )
                            {



                                String path= imagePath.getAbsolutePath();
                            resultIAV.add(path);

                            }
                        }
                //  }
                catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }

            return resultIAV;


        }

这是我的日志

11-05 05:19:25.659: W/TabsPagerAdapter(9498): inside class2 fragmentmanager
11-05 05:19:25.689: E/Bqswipeview(9498): inside onTabSelected
11-05 05:19:25.689: E/Bqswipeview(9498): tabs added
11-05 05:19:26.269: W/TabsPagerAdapter(9498): inside class2 tabspageradapter
11-05 05:19:26.269: I/System.out(9498): uri iscontent://media/external/images/media
11-05 05:19:26.269: I/System.out(9498): projection is[Ljava.lang.String;@b1155080
11-05 05:19:26.269: E/devicetab(9498): cursor not equalto null
11-05 05:19:26.269: D/AndroidRuntime(9498): Shutting down VM
11-05 05:19:26.269: W/dalvikvm(9498): threadid=1: thread exiting with uncaught exception (group=0xb0d13b20)
11-05 05:19:26.269: E/AndroidRuntime(9498): FATAL EXCEPTION: main
11-05 05:19:26.269: E/AndroidRuntime(9498): Process: com.bq.bqgdrive, PID: 9498
11-05 05:19:26.269: E/AndroidRuntime(9498): java.lang.NullPointerException
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.bq.bqgdrive.DeviceTab.getFilePaths(DeviceTab.java:185)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.bq.bqgdrive.DeviceTab.<init>(DeviceTab.java:145)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.bq.tabsswipe.adapter.TabsPagerAdapter.getItem(TabsPagerAdapter.java:28)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:327)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2291)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.View.measure(View.java:16497)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1916)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1113)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1295)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.Choreographer.doCallbacks(Choreographer.java:574)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.Choreographer.doFrame(Choreographer.java:544)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.os.Handler.handleCallback(Handler.java:733)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.os.Handler.dispatchMessage(Handler.java:95)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.os.Looper.loop(Looper.java:136)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at android.app.ActivityThread.main(ActivityThread.java:5017)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at java.lang.reflect.Method.invokeNative(Native Method)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at java.lang.reflect.Method.invoke(Method.java:515)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
11-05 05:19:26.269: E/AndroidRuntime(9498):     at dalvik.system.NativeStart.main(Native Method)

【问题讨论】：

你也可以给我们看看 logcat 吗？
嘿，我在我的问题下给了我的日志猫，请检查..

标签： android sqlite gridview android-fragments views

【解决方案1】：

我认为你必须初始化光标，然后从光标中获取任何东西，

你可以直接`getActivity().getContentResolver()。试试这个，

如果它不起作用，则显示 Log cat。

【讨论】：

下面是 logcat...我不知道这是给 log cat 的正确方法。
这不是显示任何数据的正确方式，请编辑您的问题，您将 Log cat 作为答案，这不是答案。下次要小心，否则堆栈溢出将不允许再次提问。
哦，对不起。我会检查把 mylogcat

【解决方案2】：

尝试在实例化 Fragment 时从 Activity 传递上下文，并使用此上下文而不是 getActivity() 函数。

【讨论】：

片段不应该有带参数的构造函数。

【解决方案3】：

java.lang.NullPointerException
  at com.bq.bqgdrive.DeviceTab.getFilePaths(DeviceTab.java:185)
  at com.bq.bqgdrive.DeviceTab.<init>(DeviceTab.java:145)

构造函数或成员变量初始化<init> 调用getActivity() 为时尚早。该片段尚未附加到活动。

将初始化和getFilePaths() 调用移至onAttach() 或fragment lifecycle 中的更高版本。

【讨论】：

是的，我将初始化和 getFilePaths() 方法移到了 onAttach() 但它不会工作同样的异常发生......
之前我使用 onCreate(Bundle savedInstanceState) 而不是 onAttach()

【解决方案4】：

我解决了这个问题...将发生异常的部分移至 onAttach 使用的上下文对象。更多参考请查看下面的代码

 ImageAdapter myImageAdapter;
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    activity.setContentView(R.layout.devicetab);
    Log.e("Devicetab","onCreate ");
    GridView gridview = (GridView) activity.findViewById(R.id.gridView1);
    //myImageAdapter=new ImageAdapter(this);

    ArrayList<String> arrlist=getFilePaths(activity.getApplicationContext());
    Iterator<String> itr=arrlist.iterator();

    myImageAdapter = new ImageAdapter(activity.getApplicationContext());

      do
      {
          String obj=itr.next();
//        setAdapter(obj);
          myImageAdapter.add(obj);
      }
      while(itr.hasNext());

    gridview.setAdapter(myImageAdapter);





}




     public ArrayList<String> getFilePaths(Context cntx)
        {

            Uri u =MediaStore.Images.Media.EXTERNAL_CONTENT_URI; 
            System.out.println("uri is"+u);
            String[] projection =  { MediaStore.Images.Media.DATA }; 

            Cursor c = null;

            //treeset in which images are sorted in ascending order
            SortedSet<String> dirList = new TreeSet<String>();
            ArrayList<String> resultIAV = new ArrayList<String>();

             String[] directories = null; 
            if ((u != null) &&(projection!=null)) 
            { 
                System.out.println("projection is"+projection);

                Log.e("devicetab","cursor not equalto null");

                //System.out.println("context "+getActivity().getApplicationContext());
                //here null pointer occurs

                c =cntx.getContentResolver().query(u, projection, null, null, null); 

                getActivity().startManagingCursor(c);
                c.moveToFirst();
                Log.e("devicetab","cursor");

            } 

            if ((c != null) && (c.moveToFirst())) 
            { 
                do 
                {
                    String tempDir = c.getString(0);
                    tempDir = tempDir.substring(0, tempDir.lastIndexOf("/"));
                    try{
                        dirList.add(tempDir);
                    }
                    catch(Exception e)
                    {

                    }
                } 
                while (c.moveToNext());
                //string array driectories
                directories = new String[dirList.size()];
                dirList.toArray(directories);

            }

            for(int i=0;i<dirList.size();i++)
            {
                File imageDir = new File(directories[i]);
                File[] imageList = imageDir.listFiles();



                if(imageList == null)
                    continue;
                for (File imagePath : imageList) { 
                    try {

                            if(imagePath.isDirectory())
                            {
                                imageList = imagePath.listFiles();

                            }
                            if ( imagePath.getName().contains(".jpg")|| imagePath.getName().contains(".JPG")  
                                    || imagePath.getName().contains(".jpeg")|| imagePath.getName().contains(".JPEG")                                    
                                    || imagePath.getName().contains(".png") || imagePath.getName().contains(".PNG")
                                    || imagePath.getName().contains(".gif") || imagePath.getName().contains(".GIF")
                                    || imagePath.getName().contains(".bmp") || imagePath.getName().contains(".BMP")                         
            )
                            {



                                String path= imagePath.getAbsolutePath();
                            resultIAV.add(path);

                            }
                        }

                catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }

            return resultIAV;


        }

【讨论】：