片段getActivity(). getcontentresolver ().query()返回null

Question

你好，我做了一个Fragment现在我正试图显示我所有的联系人名称给我的ListView我已经做了所有的事情，但我仍然得到Cursor null我也叫getActivity()。错误还是一样的

public class AllContacts extends Fragment {

public AllContacts() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_all_contacts, container, false);
    ListView list = (ListView) view.findViewById(R.id.listview);
    ArrayList<String> arraylist= new ArrayList<>();

    String sorting = ContactsContract.Contacts.DISPLAY_NAME+ "DESC";
    Uri uri = Uri.parse("content://ContactsContract");
    Cursor c = getActivity().getContentResolver().query(uri,null,null,null,sorting);
    while (c.moveToNext()) {
        String contactName = c.getString(c.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
        arraylist.add(contactName);
    }//end loop
       c.close();
    ArrayAdapter adapter = new ArrayAdapter(getContext(),android.R.layout.simple_list_item_1,arraylist);
    list.setAdapter(adapter);
    return view;
}
}

例外:

FATAL EXCEPTION: main
 Process: com.example.awais_pc.contactapp, PID: 25641
java.lang.NullPointerException: Attempt to invoke interface method 'boolean android.database.Cursor.moveToNext()' on a null object reference
at com.example.awais_pc.contactapp.AllContacts.onCreateView(AllContacts.java:43)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1177)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1025)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1545)
at android.view.View.measure(View.java:20151)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
at android.view.View.measure(View.java:20151)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:20151)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328)
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)
at android.view.View.measure(View.java:20151)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:20151)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:747)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:629)
at android.view.View.measure(View.java:20151)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6328)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:3158)
at android.view.View.measure(View.java:20151)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2594)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1549)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1841)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1437)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7397)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:920)
at android.view.Choreographer.doCallbacks(Choreographer.java:695)
at android.view.Choreographer.doFrame(Choreographer.java:631)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:906)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7224)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Answer 1

您的查询有两个问题，第一个是DESC关键字之前缺少空格，第二个是无效的Uri。

修改如下:

String sorting = ContactsContract.Contacts.DISPLAY_NAME+ "DESC";
Uri uri = Uri.parse("content://ContactsContract");
Cursor c = getActivity().getContentResolver().query(uri,null,null,null,sorting);

:

String sorting = ContactsContract.Contacts.DISPLAY_NAME + " DESC";
Cursor c = getActivity().getContentResolver()
    .query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,
        null, null, null, sorting);