堆栈内存溢出
  繁体   English   中英

使用片段-NullPointerException

[英]Working with fragments - NullPointerException

 原文  2014-08-15 18:36:20  6   3    java/ android/ android-activity/ android-fragments/ parse-platform

问题描述

我的活动包含多个片段，因此收到空指针异常错误。 在该活动中，将基于各种标准（例如性别，最低年龄等）通过解析将用户列表填充到当前用户。

以下是启动应用程序时意外收到的logcat消息。 

08-15 17:42:28.863: E/AndroidRuntime(4974): FATAL EXCEPTION: main
08-15 17:42:28.863: E/AndroidRuntime(4974): Process: com.dooba.beta, PID: 4974
08-15 17:42:28.863: E/AndroidRuntime(4974): java.lang.NullPointerException
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.dooba.beta.Fragment1$1.done(Fragment1.java:108)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:45)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.FindCallback.internalDone(FindCallback.java:1)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.parse.Parse$6$1.run(Parse.java:888)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.handleCallback(Handler.java:733)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.os.Looper.loop(Looper.java:136)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at java.lang.reflect.Method.invoke(Method.java:515)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-15 17:42:28.863: E/AndroidRuntime(4974):     at dalvik.system.NativeStart.main(Native Method)

以下是活动代码，其中包含发生错误的片段 

 public class usermatch extends FragmentActivity {
        private PageAdapter mPagerAdapter;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.viewpager_layout);
            initialisePaging();

        }

        private void initialisePaging() {
            // TODO Auto-generated method stub
            List<Fragment> fragments = new Vector<Fragment>();
            fragments.add(Fragment.instantiate(this, Fragment1.class.getName()));
            fragments.add(Fragment.instantiate(this, Fragment2.class.getName()));
            fragments.add(Fragment.instantiate(this, Fragment3.class.getName()));
            mPagerAdapter = new PageAdapter(this.getSupportFragmentManager(), fragments);
            ViewPager pager = (ViewPager) findViewById(R.id.viewpager);
            pager.setAdapter(mPagerAdapter);

        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {

            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.mood, menu);
            return true;
        }

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            int id = item.getItemId();
            if (id == R.id.action_settings) {
                return true;
            }
            return super.onOptionsItemSelected(item);
        }
    }

以下是我认为触发了错误的片段活动代码 

    public class Fragment1 extends Fragment {
    private String currentUserId;
    private ArrayAdapter<String> namesArrayAdapter;
    private ArrayList<String> names;
    private ListView usersListView;
    private Button logoutButton;
    String userGender = ParseUser.getCurrentUser().getString("Gender");
    String activityName = ParseUser.getCurrentUser().getString("ActivityName");
    Number maxDistance = ParseUser.getCurrentUser().getNumber("Maximum_Distance");


    String userLookingGender = ParseUser.getCurrentUser().getString("Looking_Gender");
    Number minimumAge = ParseUser.getCurrentUser().getNumber("Minimum_Age");
    Number maximumAge = ParseUser.getCurrentUser().getNumber("Maximum_Age");
    Number userage = ParseUser.getCurrentUser().getNumber("Age");


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        if (container == null){
            return null;
        }
        setConversationsList();

        return (LinearLayout)inflater.inflate(R.layout.fragment1_layout, 
                container,false);

}
private void setConversationsList() {
    currentUserId = ParseUser.getCurrentUser().getObjectId();
    names = new ArrayList<String>();
    // String userActivitySelectionName = null;

    ParseQuery<ParseUser> query = ParseUser.getQuery();

    //  query.whereEqualTo("ActivityName",userActivitySelectionName);

    query.whereNotEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
    // users with Gender = currentUser.Looking_Gender
    query.whereEqualTo("Gender", userLookingGender);
    // users with Looking_Gender = currentUser.Gender
    query.whereEqualTo("Looking_Gender", userGender);
    query.setLimit(1);
    query.whereEqualTo("ActivityName", activityName);
    query.whereGreaterThanOrEqualTo("Minimum_Age", minimumAge).whereGreaterThanOrEqualTo("Age", userage);
    query.whereLessThanOrEqualTo("Maximum_Age", maximumAge).whereLessThanOrEqualTo("Age", userage);
    //  query.whereWithinKilometers("Maximum_Distance", point, maxDistance)





    query.findInBackground(new FindCallback<ParseUser>() {

        public void done(List<ParseUser> userList, ParseException e) {
            if (e == null) {
                for (int i=0; i<userList.size(); i++) {
                    names.add(userList.get(i).get("Name").toString());
                    names.add(userList.get(i).get("Headline").toString());
                    names.add(userList.get(i).get("Age").toString());

                    //       names.add(userList.get(i).getParseObject("ProfilePicture").;


                }




                usersListView = (ListView)getActivity().findViewById(R.id.usersListView);
                namesArrayAdapter =
                        new ArrayAdapter<String>(getActivity().getApplicationContext(),
                                R.layout.user_list_item, names);
                usersListView.setAdapter(namesArrayAdapter);

                usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> a, View v, int i, long l) {
                        openConversation(names, i);
                    }
                });

            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error loading user list",
                        Toast.LENGTH_LONG).show();
            }
        }
    });
}

    public void openConversation(ArrayList<String> names, int pos) {
        ParseQuery<ParseUser> query = ParseUser.getQuery();
        query.whereEqualTo("Name", names.get(pos));
        query.findInBackground(new FindCallback<ParseUser>() {
            public void done(List<ParseUser> user, ParseException e) {
                if (e == null) {
                    Intent intent = new Intent(getActivity().getApplicationContext(), MessagingActivity.class);
                    intent.putExtra("RECIPIENT_ID", user.get(0).getObjectId());
                    startActivity(intent);
                } else {
                    Toast.makeText(getActivity().getApplicationContext(),
                            "Error finding that user",
                            Toast.LENGTH_SHORT).show();
                }
            }

        });
    }
    }

更新Logcat消息 

08-15 19:23:27.195: E/AndroidRuntime(1340): FATAL EXCEPTION: main
08-15 19:23:27.195: E/AndroidRuntime(1340): Process: com.dooba.beta, PID: 1340
08-15 19:23:27.195: E/AndroidRuntime(1340): java.lang.NullPointerException
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.dooba.beta.Fragment1$1.done(Fragment1.java:108)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.FindCallback.internalDone(FindCallback.java:45)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.FindCallback.internalDone(FindCallback.java:1)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.parse.Parse$6$1.run(Parse.java:888)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Handler.handleCallback(Handler.java:733)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.os.Looper.loop(Looper.java:136)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at android.app.ActivityThread.main(ActivityThread.java:5017)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at java.lang.reflect.Method.invokeNative(Native Method)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at java.lang.reflect.Method.invoke(Method.java:515)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
08-15 19:23:27.195: E/AndroidRuntime(1340):     at dalvik.system.NativeStart.main(Native Method)

108行 

        usersListView.setAdapter(namesArrayAdapter);

更新的活动代码 

public class Fragment1 extends Fragment {

    private String currentUserId;
    private ArrayAdapter<String> namesArrayAdapter;
    private ArrayList<String> names;
    private ListView usersListView;
    private Button logoutButton;
    String userGender = ParseUser.getCurrentUser().getString("Gender");
    String activityName = ParseUser.getCurrentUser().getString("ActivityName");
    Number maxDistance = ParseUser.getCurrentUser().getNumber("Maximum_Distance");
    String userLookingGender = ParseUser.getCurrentUser().getString("Looking_Gender");
    Number minimumAge = ParseUser.getCurrentUser().getNumber("Minimum_Age");
    Number maximumAge = ParseUser.getCurrentUser().getNumber("Maximum_Age");
    Number userage = ParseUser.getCurrentUser().getNumber("Age");

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

        setConversationsList();

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment1_layout, container, false);


        return view;
    }

private void setConversationsList() {
    currentUserId = ParseUser.getCurrentUser().getObjectId();
    names = new ArrayList<String>();
    // String userActivitySelectionName = null;

    ParseQuery<ParseUser> query = ParseUser.getQuery();

    //  query.whereEqualTo("ActivityName",userActivitySelectionName);

    query.whereNotEqualTo("objectId", ParseUser.getCurrentUser().getObjectId());
    // users with Gender = currentUser.Looking_Gender
    query.whereEqualTo("Gender", userLookingGender);
    // users with Looking_Gender = currentUser.Gender
    query.whereEqualTo("Looking_Gender", userGender);
    query.setLimit(1);
    query.whereEqualTo("ActivityName", activityName);
    query.whereGreaterThanOrEqualTo("Minimum_Age", minimumAge).whereGreaterThanOrEqualTo("Age", userage);
    query.whereLessThanOrEqualTo("Maximum_Age", maximumAge).whereLessThanOrEqualTo("Age", userage);
    //  query.whereWithinKilometers("Maximum_Distance", point, maxDistance)





    query.findInBackground(new FindCallback<ParseUser>() {

        public void done(List<ParseUser> userList, ParseException e) {
            if (e == null) {
                for (int i=0; i<userList.size(); i++) {
                    names.add(userList.get(i).get("Name").toString());
                    names.add(userList.get(i).get("Headline").toString());
                    names.add(userList.get(i).get("Age").toString());

                    //       names.add(userList.get(i).getParseObject("ProfilePicture").;


                }




                usersListView = (ListView)getActivity().findViewById(R.id.usersListView);
                namesArrayAdapter =
                        new ArrayAdapter<String>(getActivity().getApplicationContext(),
                                R.layout.user_list_item, names);
                usersListView.setAdapter(namesArrayAdapter);

                usersListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> a, View v, int i, long l) {
                        openConversation(names, i);
                    }
                });

            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error loading user list",
                        Toast.LENGTH_LONG).show();
            }
        }
    });
}

public void openConversation(ArrayList<String> names, int pos) {
    ParseQuery<ParseUser> query = ParseUser.getQuery();
    query.whereEqualTo("Name", names.get(pos));
    query.findInBackground(new FindCallback<ParseUser>() {
        public void done(List<ParseUser> user, ParseException e) {
            if (e == null) {
                Intent intent = new Intent(getActivity().getApplicationContext(), MessagingActivity.class);
                intent.putExtra("RECIPIENT_ID", user.get(0).getObjectId());
                startActivity(intent);
            } else {
                Toast.makeText(getActivity().getApplicationContext(),
                        "Error finding that user",
                        Toast.LENGTH_SHORT).show();
            }
        }
    });
}
}

我有些困惑，即使进行了研究，我也很难找到并解决问题。 请指教，在此先感谢

3 个解决方案

解决方案1
 2  2014-08-15 18:45:25

同样，您在onActivityCreated() getActivity()之前调用getActivity() ，因此getActivity()返回null。

在onActivityCreated()之前调用onCreateView() onActivityCreated() 。 Called when the activity's onCreate() method has returned. onActivityCreated() Called when the activity's onCreate() method has returned. 这意味着调用onCreateView()时，片段的getActivitiy()方法将返回null。

在onCreateView()您可以调用setConversationsList() ，它可以在多个位置访问getActivity() 。 因此， NullPointerException 。

解决方案2
 1  2014-08-15 18:48:46

在迭代之前，您可能需要检查List<ParseUser> userList是否为null。

解决方案3
 1 已采纳  2014-08-15 19:02:48

如果您在setConversationsList()中找到的视图来自片段的布局（ R.layout.fragment1_layout ），则必须首先为布局充气： 

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment1_layout, container, false);

    setConversationsList();

    return view;
}

请注意，在onActivityCreated之前使用getActivity是完全正常的，因为自onAttach以来已经可用。 但是，如果要查找的视图属于活动的布局，则应在onActivityCreated找到它们。

暂无
暂无

声明:本站的技术帖子网页，遵循CC BY-SA 4.0协议，如果您需要转载，请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.

相关问题 NullPointerException-使用片段中的位置 使用带有片段的节，NullPointerException 使用带有textview的片段的NullPointerException Android Fragments NullPointerException错误 NullPointerException，带有片段和自定义列表 片段捆绑：NullPointerException 在片段中获取NullPointerException错误 Robolectric使用Fragments和ActionBarCompat NullPointerException 在片段和活动之间交换数据-NullPointerException 使用ActionBarSherlock片段的按钮中的NullPointerException setOnClickListener
相关标签
 
粤ICP备18138465号  © 2020-2024 STACKOOM.COM