Question

我有一个错误，我无法排除故障。该程序有效，但当设备空闲并且我恢复到应用程序时它会崩溃。基本上，我的代码所做的是获得用户的邀请。它显示从多个用户收到的邀请，我可以选择接受或拒绝邀请。 0表示拒绝邀请，1表示接受邀请。我正在使用解析BaaS。我收到此错误并且无法解决问题，请需要一些帮助：

错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
            at android.widget.ArrayAdapter.init(ArrayAdapter.java:310)
            at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:153)
            at com.example.davchen.skibuddies.Fragments.InviteTab$2.<init>(InviteTab.java:93)
            at com.example.davchen.skibuddies.Fragments.InviteTab.updateList(InviteTab.java:92)
            at com.example.davchen.skibuddies.Fragments.InviteTab.access$200(InviteTab.java:35)
            at com.example.davchen.skibuddies.Fragments.InviteTab$1.done(InviteTab.java:81)
            at com.example.davchen.skibuddies.Fragments.InviteTab$1.done(InviteTab.java:69)
            at com.parse.ParseTaskUtils$2$1.run(ParseTaskUtils.java:115)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:145)
            at android.app.ActivityThread.main(ActivityThread.java:5942)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

以下是我的代码：

public class InviteTab extends Fragment {

    private static final String TAG = InviteTab.class.getSimpleName();

    private List<Invitation> invites;
    private ListView inviteList;
    private Invitation invitation;

    public InviteTab() {}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        invites =  new ArrayList<Invitation>();
        invitation = new Invitation();
    }

   // @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        //return super.onCreateView(inflater, container, savedInstanceState);
        View rootView = inflater.inflate(R.layout.invite_tab_fragment, container, false);
        inviteList = (ListView)rootView.findViewById(R.id.invitationList);
        queryEventListFromParse();
        return rootView;
    }

    private void queryEventListFromParse() {

        ParseQuery<ParseObject> query = ParseQuery.getQuery("Invitation");
        query.whereEqualTo("Participants", ParseUser.getCurrentUser());
        query.whereEqualTo("Status", "0");
        query.include("EventId");
        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> Objects, ParseException e) {
                if (e == null) {
                    Log.d(TAG, "Check if program enters loop");
                    invites.clear();
                    for (ParseObject EventInvite : Objects) {
                        invites.add((Invitation) EventInvite);
                    }
                    Log.d(TAG, String.valueOf(invites.size()));
                    updateList(); //update the list
                } else {
                    Log.d(TAG, "Unable to retreive Invites: " + e.getMessage());
                }

            }
        });
    }

    private void updateList() {

        ArrayAdapter<Invitation> adapter = new ArrayAdapter<Invitation>(getActivity(),
                R.layout.invitation_list, invites) {
            @Override
            public View getView(final int position, View convertView, ViewGroup parent) {

                if(convertView==null) {
                    convertView = getActivity().getLayoutInflater().inflate(R.layout.invitation_list, parent, false);
                }
                TextView Title = (TextView)convertView.findViewById(R.id.eventName);
                Button button1 =(Button)convertView.findViewById(R.id.acceptButton);
                Button button2 = (Button)convertView.findViewById(R.id.rejectButton);
                //TextView tvStart = (TextView)convertView.findViewById(R.id.textView_start);
               // TextView tvEnd = (TextView)convertView.findViewById(R.id.textView_end);

                invitation = invites.get(position);

                Title.setText(invitation.getEventId().get("EventTitle").toString());
//                tvStart.setText(event.getStartTime());
//                tvEnd.setText(event.getEndTime());

                button1.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        updateStatus(position);
                    }
                });

                return convertView;
            }

            @Override
            public int getCount() {
                return super.getCount();
            }
        };

        Log.d(TAG, "Was in adapter method");
        inviteList.setAdapter(adapter);

    }

    private void updateStatus(int position) {
        Invitation invite = invites.get(position);

        invite.setUserId(ParseUser.getCurrentUser());
        invite.setFlag("1");
        invite.saveInBackground(new SaveCallback() {
            @Override
            public void done(ParseException e) {
                if(e==null) {
                    Toast.makeText(getActivity().getApplicationContext(), "Accepted Request", Toast.LENGTH_LONG).show();
                }
                else{
                    Log.e(TAG, e.getMessage());
                }
            }
        });
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
    }

    @Override
    public void onDetach() {
        super.onDetach();
    }

    @Override
    public void onResume() {
        super.onResume();
        queryEventListFromParse();
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode == getActivity().RESULT_OK) {
            // If a new event has been added, update the list of events
            Log.d(TAG, "Hello");
            queryEventListFromParse();
        }
    }
}

Answer 1

不要使用getActivity()方法be'coz片段de附加当应用程序进入后台并在之后打开时。

请参阅fragment life cycle

在将片段附加到actvity

时初始化context

@Override
public void onAttach(Activity context) {
    super.onAttach(context);
    this.context = context;
}

将代码放入onActivityCreated并使用context而不是getActivity()

 @Override
    public void onActivityCreated(Bundle savedInstanceState) {
     super.onActivityCreated(savedInstanceState);
    queryEventListFromParse();

}

程序在几分钟后崩溃或在闲置几分钟后恢复

1 个答案: