空指针异常错误android

Question

我的片段类中出现空指针异常错误。 我在程序中使用选项卡活动，列表视图位于片段xml文件中。 码：

    package com.example.timetracker;

import ///


public class MainActivity extends FragmentActivity implements
ActionBar.TabListener, LoaderCallbacks<Cursor> {

    private static String TAG = "MainActivity";
    private static final int CM_DELETE_ID = 1;
    private static final int RESET_STOPWATCH = 2;
    static ListView lvData;
    static DB db;
    static SimpleCursorAdapter scAdapter;
    static Activity act;

    SectionsPagerAdapter mSectionsPagerAdapter;
    ViewPager mViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        //create my tabs...
        }
    }


    //some code...

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a DummySectionFragment (defined as a static inner class
            // below) with the page number as its lone argument.
            if(position == 0){  
                Fragment fragment = new DummySectionFragment();
                Bundle args = new Bundle();
                args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
                fragment.setArguments(args);
                return fragment;
            }

            if (position == 1)
            {
                Fragment fragment2 = new DummySectionFragment2();
                Bundle args = new Bundle();
                args.putInt(DummySectionFragment2.ARG_SECTION_NUMBER, position + 2);
                fragment2.setArguments(args);
                return fragment2;
            }
            return null;

        }


        @Override
        public int getCount() {
            return 2;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            Locale l = Locale.getDefault();
            switch (position) {
            case 0:
                return getString(R.string.title_section1).toUpperCase(l);
            case 1:
                return getString(R.string.title_section2).toUpperCase(l);
            }
            return null;
        }

    }

    public static class DummySectionFragment extends Fragment{

        public static final String ARG_SECTION_NUMBER = "section_number";
        public DummySectionFragment() {
        }

        View v;

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.activity_tracker,
                    container, false);
            v = inflater.inflate(R.layout.activity_statistic,
                    container, false);
            createList();
            return rootView;
        }

        public void createList(){
            db = new DB(act);Log.d(TAG, "1");
            db.open();Log.d(TAG, "2");

            String[] from = new String[] {DB.COLUMN_NAME, DB.COLUMN_TIME  };Log.d(TAG, "3");
            int[] to = new int[] { R.id.tvTextName, R.id.tvText_time};Log.d(TAG, "4");

            scAdapter = new SimpleCursorAdapter(act, R.layout.item, null, from, to, 0);Log.d(TAG, "5");
            lvData = (ListView) v.findViewById(R.id.lvData);Log.d(TAG, "6 ");
                    //after thap i have error
            lvData.setAdapter(scAdapter);Log.d(TAG, "7");
        }
    }

    public static class DummySectionFragment2 extends Fragment implements LoaderCallbacks<Cursor>  {
            //some code....
            }


        @Override
        public Loader<Cursor> onCreateLoader(int arg0, Bundle arg1) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public void onLoadFinished(Loader<Cursor> arg0, Cursor arg1) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onLoaderReset(Loader<Cursor> arg0) {
            // TODO Auto-generated method stub

        }
    }

    //Data base class
    static class MyCursorLoader extends CursorLoader {

        DB db;

        public MyCursorLoader(Context context, DB db) {
            super(context);
            this.db = db;
        }

        @Override
        public Cursor loadInBackground() {
            Cursor cursor = db.getAllData();
            return cursor;
        }

    }

}

请勿使用代码“ lvData.setAdapter（scAdapter）; Log.d（TAG，“ 7”）;“ 日志：

  04-03 20:11:54.830: D/dalvikvm(1684): GC_FOR_ALLOC freed 97K, 6% free 2883K/3040K, paused 9ms, total 9ms
04-03 20:11:54.850: D/MainActivity(1684): 1
04-03 20:11:54.850: D/Data Base(1684): Открытие Подключения
04-03 20:11:54.858: D/Data Base(1684): Подключение открыто
04-03 20:11:54.858: D/MainActivity(1684): 2
04-03 20:11:54.858: D/MainActivity(1684): 3
04-03 20:11:54.858: D/MainActivity(1684): 4
04-03 20:11:54.858: D/MainActivity(1684): 6 
04-03 20:11:54.858: D/MainActivity(1684): 5
04-03 20:11:54.858: D/AndroidRuntime(1684): Shutting down VM
04-03 20:11:54.858: W/dalvikvm(1684): threadid=1: thread exiting with uncaught exception (group=0xa4c41648)
04-03 20:11:54.858: E/AndroidRuntime(1684): FATAL EXCEPTION: main
04-03 20:11:54.858: E/AndroidRuntime(1684): java.lang.NullPointerException
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.example.timetracker.MainActivity$DummySectionFragment.createList(MainActivity.java:200)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.example.timetracker.MainActivity$DummySectionFragment.onCreateView(MainActivity.java:187)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.View.measure(View.java:15848)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.View.measure(View.java:15848)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:302)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.View.measure(View.java:15848)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5012)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2189)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.View.measure(View.java:15848)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1905)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1104)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1284)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.Choreographer.doCallbacks(Choreographer.java:562)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.Choreographer.doFrame(Choreographer.java:532)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.os.Handler.handleCallback(Handler.java:730)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.os.Looper.loop(Looper.java:137)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at android.app.ActivityThread.main(ActivityThread.java:5103)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at java.lang.reflect.Method.invokeNative(Native Method)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at java.lang.reflect.Method.invoke(Method.java:525)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-03 20:11:54.858: E/AndroidRuntime(1684):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您对v.findViewById(R.id.lvData);调用v.findViewById(R.id.lvData); 返回null。 这似乎是因为您尚未在名为v的结构中放入任何视图。 然后，您尝试在下面的行上使用null，这就是导致异常的原因。