Question

我试图使用解析用户对象和findInBackground从Parse数据库中检索android中的名称列表但是我得到了FATAL EXCEPTION：main java.lang.NullPointerException

package com.example.user.chat;

import android.app.ActionBar;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import com.example.user.mycareerchat.custom.CustomActivity;
import com.example.user.mycareerchat.utils.Utils;
import com.parse.FindCallback;
import com.parse.ParseException;
import com.parse.ParseQuery;
import com.parse.ParseUser;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by user on 26/Aug/2015.
 */
public class UserList extends CustomActivity{

    private static final String EXTRA_DATA = null ;
    private ArrayList<ParseUser> uList;

    public static ParseUser user;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.user_list);




        /*getActionBar().setDisplayHomeAsUpEnabled(false);*/

       updateUserStatus(true);


    }


    @Override
    protected void onDestroy() {
        super.onDestroy();

        updateUserStatus(false);
    }


    @Override
    protected void onResume() {
        super.onResume();
       loadUserList();
    }

    private void updateUserStatus(boolean online) {

        user.put("online", online);
        user.saveEventually();

    }

    private void loadUserList(){

        final ProgressDialog dia = ProgressDialog.show(this, null, getString(R.string.alert_loading));

        ParseUser.getQuery().whereNotEqualTo("username",user.getUsername()).findInBackground(new FindCallback<ParseUser>() {

            @Override
            public void done(List<ParseUser> li, ParseException e) {
                dia.dismiss();
                if (li != null) {

                    if (li.size() == 0) {
                        Toast.makeText(UserList.this, getString(R.string.msg_no_user_found), Toast.LENGTH_SHORT).show();

                        ListView list = (ListView) findViewById(R.id.list);
                        uList = new ArrayList<ParseUser>(li);

                        list.setAdapter(new UserAdapter());
                        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                            @Override
                            public void onItemClick(AdapterView<?> arg0, View arg1, int pos, long arg3) {

                                startActivity(new Intent(UserList.this, Chat.class).putExtra(EXTRA_DATA, uList.get(pos).getUsername()));


                            }
                        });
                    }

                    else {

                        Utils.showDialog(UserList.this, getString(R.string.err_users) + " " + e.getMessage());
                    }


                }
            }
        });
    }

    private class UserAdapter extends BaseAdapter {
        @Override
        public int getCount() {

            return uList.size();
        }

        @Override
        public ParseUser getItem(int arg0) {
            return uList.get(arg0);
        }

        @Override
        public long getItemId(int arg0) {
            return arg0;
        }

        @Override
        public View getView(int pos, View v, ViewGroup arg2) {

            if(v!=null)
                v=getLayoutInflater().inflate(R.layout.chat_item,null);

            ParseUser c= getItem(pos);
            TextView lbl = (TextView) v;
            lbl.setText(c.getUsername());
            lbl.setCompoundDrawablesWithIntrinsicBounds(c.getBoolean("online")? R.drawable.ic_online:
                    R.drawable.ic_offline,
                    0,R.drawable.arrow,0);
            return v;
        }
    }
}

错误

08-27 18：54：06.039 16446-16446 / com.example.user.mycareerchat E / AndroidRuntime：FATAL EXCEPTION：main 显示java.lang.NullPointerException 在com.example.user.mycareerchat.UserList $ 1.done（UserList.java:106）在com.example.user.mycareerchat.UserList $ 1.done（UserList.java:79）在com.parse.ParseTaskUtils $ 2 $ 1.run（ParseTaskUtils.java:115）在android.os.Handler.handleCallback（Handler.java:725）在android.os.Handler.dispatchMessage（Handler.java:92）在android.os.Looper.loop（Looper.java:137）在android.app.ActivityThread.main（ActivityThread.java:5041） at java.lang.reflect.Method.invokeNative（Native Method）在java.lang.reflect.Method.invoke（Method.java:511）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:793）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:560）在dalvik.system.NativeStart.main（本地方法）

Answer 1

这是整个UserList课吗？因为在提供的代码中，您只声明并使用user对象，而不为其分配ParseUser的实例。

public static ParseUser user; // Only a declaration, "user" still null

因此，user.getUsername()会导致nullpointer异常，因为

时user仍为null

ParseUser.getQuery().whereNotEqualTo("username",user.getUsername()).findInBackground(new FindCallback<ParseUser>() {

您必须为user分配ParseUser类型的对象（或ParseUser的子类）：

public static ParseUser user;
user = new ParseUser(..., args, ...); // Now user is not null anymore and the object's methods can be called

从Parse数据库中检索android中的名称列表

1 个答案: