由于某种原因，我的应用程序因空指针异常而一直崩溃。我正在为每个页面使用带有片段的导航抽屉。我也使用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，如果我再次选择相同的片段或尝试转到另一个片段，则应用程序崩溃。
我能够找出问题所在。它在尝试呼叫时崩溃：
installDir = "your/install/dir"
...
install.packages("yourPackage", dir=installDir)
第二次。
以下是两个片段的代码：
排名片段：
st = conn.createStatement();
每周比赛片段：
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;
}
}
}
logcat的：
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;
}
}
}
任何帮助都将非常感谢!!!
答案 0 :(得分：0)
在onViewCreated中重温您的方法StandingsFragment。
检查resultList或您的某个观点（例如player1）是否为空
答案 1 :(得分：0)
我认为在AsyncTask中使用onViewCreated不是正确的方法来进行数据库操作。此外，您正在使用get()方法，onViewCreated也在Thread上运行。
因此，您应该使用简单的函数而不是AsyncTask。
<强> Editted
好吧，
第一：我不知道我错了：D。
第二：我仍然不确定在Thread中连接数据库是否必要
第三：我在Runnable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();
检查一下：
Android Sqlite getReadableDatabase
答案 2 :(得分：0)
问题是连接以某种方式关闭，而不是正确地重新打开。通过保持连接打开（不调用conn.close（））一切正常。