Android 应用程序不断因空指针异常而崩溃
Posted
技术标签:
【中文标题】Android 应用程序不断因空指针异常而崩溃【英文标题】：Android Application Keeps Crashing from Null Pointer Exception 【发布时间】：2015-07-04 06:54:05 【问题描述】：由于某种原因，我的应用程序由于空指针异常而不断崩溃。我正在为我的每个页面使用带有片段的导航抽屉。我还使用 JDBC 连接到我的 oracle 数据库。我遇到的问题是我的两个片段。当我运行程序时，无论我选择第一个片段还是第二个片段，它都可以正常工作。但是如果我再次选择同一个片段或尝试转到另一个片段，那么应用程序就会崩溃。
我能够查明问题所在。它在尝试调用时崩溃：
st = conn.createStatement();
第二次。
这是两个片段的代码：
排名片段：
package com.capstone.hammond.wallstreetfantasyleaguefinal;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
public class StandingsFragment extends Fragment
List<Integer> idList = new ArrayList<>();
List<String> winList = new ArrayList<>();
List<String> lossList = new ArrayList<>();
List<String> firstName = new ArrayList<>();
List<String> lastName = new ArrayList<>();
int resultID;
String resultWins;
String resultLosses;
String firstNameS;
String lastNameS;
Connection conn;
ResultSet rs, rs1, rs2, rs3, rs4, rs5, rs6;
Statement st, st1, st2, st3, st4, st5, st6;
View rootview;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
rootview = inflater.inflate(R.layout.fragment_standings, container, false);
return rootview;
public void onViewCreated(View view, Bundle savedInstanceState)
super.onViewCreated(view, savedInstanceState);
try
List<List> resultList = new Standings().execute().get();
firstName = resultList.get(0);
lastName = resultList.get(1);
winList = resultList.get(2);
lossList = resultList.get(3);
TextView player1;
TextView player2;
TextView player3;
TextView player4;
TextView player5;
TextView player6;
TextView player1Win;
TextView player2Win;
TextView player3Win;
TextView player4Win;
TextView player5Win;
TextView player6Win;
TextView player1Loss;
TextView player2Loss;
TextView player3Loss;
TextView player4Loss;
TextView player5Loss;
TextView player6Loss;
player1 = (TextView) view.findViewById(R.id.player1);
player1.setText(firstName.get(0) + " " + lastName.get(0));
player2 = (TextView) view.findViewById(R.id.player2);
player2.setText(firstName.get(1) + " " + lastName.get(1));
player3 = (TextView) view.findViewById(R.id.player3);
player3.setText(firstName.get(2) + " " + lastName.get(2));
player4 = (TextView) view.findViewById(R.id.player4);
player4.setText(firstName.get(3) + " " + lastName.get(3));
player5 = (TextView) view.findViewById(R.id.player5);
player5.setText(firstName.get(4) + " " + lastName.get(4));
player6 = (TextView) view.findViewById(R.id.player6);
player6.setText(firstName.get(5) + " " + lastName.get(5));
player1Win = (TextView) view.findViewById(R.id.player1_win);
player1Win.setText(winList.get(0));
player2Win = (TextView) view.findViewById(R.id.player2_win);
player2Win.setText(winList.get(1));
player3Win = (TextView) view.findViewById(R.id.player3_win);
player3Win.setText(winList.get(2));
player4Win = (TextView) view.findViewById(R.id.player4_win);
player4Win.setText(winList.get(3));
player5Win = (TextView) view.findViewById(R.id.player5_win);
player5Win.setText(winList.get(4));
player6Win = (TextView) view.findViewById(R.id.player6_win);
player6Win.setText(winList.get(5));
player1Loss = (TextView) view.findViewById(R.id.player1_loss);
player1Loss.setText(lossList.get(0));
player2Loss = (TextView) view.findViewById(R.id.player2_loss);
player2Loss.setText(lossList.get(1));
player3Loss = (TextView) view.findViewById(R.id.player3_loss);
player3Loss.setText(lossList.get(2));
player4Loss = (TextView) view.findViewById(R.id.player4_loss);
player4Loss.setText(lossList.get(3));
player5Loss = (TextView) view.findViewById(R.id.player5_loss);
player5Loss.setText(lossList.get(4));
player6Loss = (TextView) view.findViewById(R.id.player6_loss);
player6Loss.setText(lossList.get(5));
catch(InterruptedException e)
e.printStackTrace();
catch(ExecutionException e)
e.printStackTrace();
public class Standings extends AsyncTask<Void, Void, List<List>>
@Override
protected List<List> doInBackground(Void... params)
try
conn = ConnectionManager.getConnection();
rs = null;
st = null;
if (conn != null)
st = conn.createStatement();
if (st != null)
rs = st.executeQuery("SELECT * FROM L1_STANDINGS");
if (rs != null)
while(rs.next())
resultID = rs.getInt("USERID");
idList.add(resultID);
resultWins = rs.getString("WINS");
winList.add(resultWins);
resultLosses = rs.getString("LOSSES");
lossList.add(resultLosses);
st1 = null;
if (conn != null)
st1 = conn.createStatement();
rs1 = null;
if (st1 != null)
rs1 = st1.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(0)));
if (rs1 != null)
while(rs1.next())
firstNameS = rs1.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs1.getString("LASTNAME");
lastName.add(lastNameS);
st2 = null;
if (conn != null)
st2 = conn.createStatement();
rs2 = null;
if (st2 != null)
rs2 = st2.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(1)));
if (rs2 != null)
while(rs2.next())
firstNameS = rs2.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs2.getString("LASTNAME");
lastName.add(lastNameS);
st3 = null;
if (conn != null)
st3 = conn.createStatement();
rs3 = null;
if (st3 != null)
rs3 = st3.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(2)));
if (rs3 != null)
while(rs3.next())
firstNameS = rs3.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs3.getString("LASTNAME");
lastName.add(lastNameS);
st4 = null;
if (conn != null)
st4 = conn.createStatement();
rs4 = null;
if (st4 != null)
rs4 = st4.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(3)));
if (rs4 != null)
while(rs4.next())
firstNameS = rs4.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs4.getString("LASTNAME");
lastName.add(lastNameS);
st5 = null;
if (conn != null)
st5 = conn.createStatement();
rs5 = null;
if (st5 != null)
rs5 = st5.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(4)));
if (rs5 != null)
while(rs5.next())
firstNameS = rs5.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs5.getString("LASTNAME");
lastName.add(lastNameS);
st6 = null;
if (conn != null)
st6 = conn.createStatement();
rs6 = null;
if (st6 != null)
rs6 = st6.executeQuery("SELECT * FROM USERINFO WHERE USERID = " + (idList.get(5)));
if (rs6 != null)
while(rs6.next())
firstNameS = rs6.getString("FIRSTNAME");
firstName.add(firstNameS);
lastNameS = rs6.getString("LASTNAME");
lastName.add(lastNameS);
List<List> resultList = new ArrayList<>();
resultList.add(firstName);
resultList.add(lastName);
resultList.add(winList);
resultList.add(lossList);
return resultList;
catch (SQLException e)
e.printStackTrace();
finally
try
if(rs!=null)
rs.close();
if(rs1!=null)
rs1.close();
if(rs2!=null)
rs2.close();
if(rs3!=null)
rs3.close();
if(rs4!=null)
rs4.close();
if(rs5!=null)
rs5.close();
if(rs6!=null)
rs6.close();
if(st!=null)
st.close();
if(st1!=null)
st1.close();
if(st2!=null)
st2.close();
if(st3!=null)
st3.close();
if(st4!=null)
st4.close();
if(st5!=null)
st5.close();
if(st6!=null)
st6.close();
if(conn!=null)
conn.close();
catch(SQLException e)
e.printStackTrace();
return null;
每周匹配片段：
package com.capstone.hammond.wallstreetfantasyleaguefinal;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
public class WeeklyMatchFragment extends Fragment
Connection conn;
ResultSet rs, rs1, rs2;
Statement st, st1, st2;
View rootview;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
rootview = inflater.inflate(R.layout.fragment_weekly_match, container, false);
return rootview;
public void onViewCreated(View view, Bundle savedInstanceState)
super.onViewCreated(view, savedInstanceState);
try
TextView user1;
TextView user2;
TextView bank1;
TextView bank2;
List<String> resultList = new MatchDetails().execute().get();
user1 = (TextView) view.findViewById(R.id.player1);
user1.setText(UserLoginInfo.fName + " " + UserLoginInfo.lName);
bank1 = (TextView) view.findViewById(R.id.bank1);
bank1.setText("Bank: $" + resultList.get(0));
user2 = (TextView) view.findViewById(R.id.user2);
user2.setText(resultList.get(1) + " " + resultList.get(2));
bank2 = (TextView) view.findViewById(R.id.bank2);
bank2.setText("Bank: $" + resultList.get(3));
catch(InterruptedException e)
e.printStackTrace();
catch(ExecutionException e)
e.printStackTrace();
public class MatchDetails extends AsyncTask<Void, Void, List<String>>
@Override
protected List<String> doInBackground(Void... params)
try
List<String> resultList = new ArrayList<>();
conn = ConnectionManager.getConnection();
rs = null;
st = null;
if (conn != null)
st = conn.createStatement();
if (st != null)
rs = st.executeQuery("SELECT * FROM L1_STANDINGS WHERE EMAIL = '" + UserLoginInfo.userEmail + "'");
if (rs != null)
while(rs.next())
resultList.add(rs.getString("BANK"));
UserLoginInfo.currOpp = rs.getInt("CURR_OPP");
st1 = null;
if (conn != null)
st1 = conn.createStatement();
rs1 = null;
if (st1 != null)
rs1 = st1.executeQuery("SELECT * FROM USERINFO WHERE USERID = '" + UserLoginInfo.currOpp + "'");
if (rs1 != null)
while(rs1.next())
resultList.add(rs1.getString("FIRSTNAME"));
resultList.add(rs1.getString("LASTNAME"));
rs2 = null;
st2 = null;
if (conn != null)
st2 = conn.createStatement();
if (st2 != null)
rs2 = st.executeQuery("SELECT * FROM L1_Standings WHERE USERID = '" + UserLoginInfo.currOpp + "'");
if (rs2 != null)
while(rs2.next())
resultList.add(rs2.getString("BANK"));
return resultList;
catch (SQLException e)
e.printStackTrace();
finally
try
if(rs!=null)
rs.close();
if(rs1!=null)
rs1.close();
if(st!=null)
st.close();
if(st1!=null)
st1.close();
if(conn!=null)
conn.close();
catch(SQLException e)
e.printStackTrace();
return null;
LogCat：
04-25 12:55:55.151: E/AndroidRuntime(2409): FATAL EXCEPTION: main
04-25 12:55:55.151: E/AndroidRuntime(2409): Process: com.capstone.hammond.wallstreetfantasyleaguefinal, PID: 2409
04-25 12:55:55.151: E/AndroidRuntime(2409): java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference
04-25 12:55:55.151: E/AndroidRuntime(2409): at com.capstone.hammond.wallstreetfantasyleaguefinal.StandingsFragment.onViewCreated(StandingsFragment.java:72)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:971)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1136)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1499)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:456)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.os.Handler.handleCallback(Handler.java:739)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.os.Handler.dispatchMessage(Handler.java:95)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.os.Looper.loop(Looper.java:135)
04-25 12:55:55.151: E/AndroidRuntime(2409): at android.app.ActivityThread.main(ActivityThread.java:5221)
04-25 12:55:55.151: E/AndroidRuntime(2409): at java.lang.reflect.Method.invoke(Native Method)
04-25 12:55:55.151: E/AndroidRuntime(2409): at java.lang.reflect.Method.invoke(Method.java:372)
04-25 12:55:55.151: E/AndroidRuntime(2409): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
04-25 12:55:55.151: E/AndroidRuntime(2409): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
任何帮助将不胜感激！！！
【问题讨论】：
似乎问题出在 com.capstone.hammond.wallstreetfantasyleaguefinal.StandingsFragment.onViewCreated(StandingsFragment.java:72) 日志几乎总结了这个问题。List<List> resultList = new Standings().execute().get(); 在这里，resultList 是 null，随后对空引用的任何调用都将导致 NullPointerException。如果您显示的异常是日志中唯一的异常，则表示您没有从与您的查询对应的数据库中获得任何结果。
我只是不明白为什么我第一次打开它时它会工作，然后如果我再次尝试打开它就会崩溃。
@MikeHammond 我向您保证，您自己可以更快地找到此问题的根本原因，因为您可以在最后重现它。
【参考方案1】：
在StandingsFragment 中重新访问您的方法onViewCreated。
检查resultList 或您的视图之一（例如player1）是否为空
【讨论】：
是的 resultList 在我第二次尝试时变为空。【参考方案2】：我认为在onViewCreated 中使用AsyncTask 不是用于数据库操作的正确方法。此外，您正在使用get() 方法，onViewCreated 也在线程上运行。 因此，您应该只使用简单函数而不是 AsyncTask。
已编辑 好的， 第一：我不知道我错了：D。 第二：我仍然不确定是否有必要在 Thread 中连接数据库。 第三：我在 Runnable 中做过 :( 这里是：
public class Items extends Fragment
private DBViewOperation mDBViewOp;
private ArrayList<DashboardItem> items;
private Runnable runnable;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
mDBViewOp = new DBViewOperation(getActivity());
/* It is not funny :/ */
runnable= new Runnable()
@Override
public void run()
loadItems();
getActivity().runOnUiThread(runnable);
private void loadItems()
items = mDBViewOp.GetItems(groupID);
int size = items.size();
int flashCount = 0;//....
不要使用conn.createStatement();
检查这个：Android Sqlite getReadableDatabase
【讨论】：
您无法连接到主线程上的数据库。我相信您必须在 AsyncTask 中执行此操作。 不，我最近写了一个在主线程中连接的片段。如果你愿意，我可以与你分享。 那太好了。【参考方案3】：问题是连接以某种方式关闭并且没有正确重新打开。通过保持连接打开（不调用 conn.close()）一切正常。
【讨论】：
以上是关于Android 应用程序不断因空指针异常而崩溃的主要内容，如果未能解决你的问题，请参考以下文章
可滑动视图空异常错误 - Android Studio [重复]