User358218
Reputation: 523
Error with android database program
06-29 01:24:15.882: ERROR/AndroidRuntime(747): Uncaught handler: thread main exiting due to uncaught exception
06-29 01:24:15.922: ERROR/AndroidRuntime(747): java.lang.RuntimeException: Unable to start activity ComponentInfo{one.two/one.two.Arrival}: java.lang.NullPointerException
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2268)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2284)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread.access$1800(ActivityThread.java:112)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1692)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.os.Handler.dispatchMessage(Handler.java:99)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.os.Looper.loop(Looper.java:123)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread.main(ActivityThread.java:3948)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at java.lang.reflect.Method.invokeNative(Native Method)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at java.lang.reflect.Method.invoke(Method.java:521)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at dalvik.system.NativeStart.main(Native Method)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): Caused by: java.lang.NullPointerException
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at one.two.DBAdapter.getAllTitles(DBAdapter.java:167)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at one.two.Arrival.getData(Arrival.java:35)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at one.two.Arrival.onCreate(Arrival.java:21)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231)
06-29 01:24:15.922: ERROR/AndroidRuntime(747): ... 11 more
My Class to call the database
package one.two;
import java.util.ArrayList;
import java.util.List;
import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class Arrival extends ListActivity
{
private ListView listView;
DBAdapter db = new DBAdapter(this);
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
getData();
// db.open();
listView = (ListView) findViewById(android.R.id.list);
// db.close();
}
private void getData()
{
// show some display that you are going to open db
db.open();
// show some display that you have opened
// redundant see below statement ---- List<String> items = new ArrayList<String>();
// call the DBAdapter method to getAllTitles()
List<String> items = DBAdapter.getAllTitles();
// iterate through the items one by one thru display statement or show
// on layout
// check how to do that
ArrayAdapter<String> titles = new ArrayAdapter<String>(this,
R.layout.main, items);
db.close();
}
}
My DBAdapter.java
package one.two;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.List;
import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import java.util.ArrayList;
public class DBAdapter extends ListActivity
{
private static String DB_PATH = "/data/data/one.two/databases/";
private static final String DATABASE_NAME = "ferry.db";
private static final String DATABASE_TABLE = "port";
public static Context context;
public String status = "status";
public String id = "id";
public String arrival = "arrival";
public String destination = "destination";
public String ferry = "ferry";
//null constructor
public DBAdapter()
{
}
//overloaded non-null constructor
public DBAdapter(Context context)
{
}
public class DatabaseHelper extends SQLiteOpenHelper
{
Context context;
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context = context;
}//end constructor DatabaseHelper
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
}//end onUpgrade()
@Override
public void onCreate(SQLiteDatabase db)
{
boolean dbExist = checkDatabase();
if (dbExist)
{
}
else
{
this.getReadableDatabase();
try
{
copyDataBase();
}
catch (IOException e)
{
throw new Error("Error copying database");
}
}
}//end onCreate()
}// end class DatabaseHelper
private static DatabaseHelper DBHelper;
private static SQLiteDatabase db;
private static final int DATABASE_VERSION = 1;
//// context brought up /////////////
//private final Context context;
private boolean checkDatabase()
{
SQLiteDatabase checkDB = null;
try
{
String myPath = DB_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}
catch (SQLiteException e)
{
// database doesn't exist yet
}
if (checkDB != null)
{
checkDB.close();
}
return checkDB != null ? true : false;
}//end checkDatabase()
private void copyDataBase() throws IOException
{
// Open your local db as the input stream
InputStream myInput = context.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DATABASE_NAME;
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0)
{
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}//end copyDataBase()
public void DBAdapter() throws SQLException
{
String myPath = DB_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}//end DBAdapter()
public void open()
{
//Open the database
String myPath = DB_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
// ---closes the database---
public void close()
{
DBHelper.close();
}//end close()
public static List<String> getAllTitles()
{
List<String> titles = new ArrayList<String>();
Cursor c=null;
c = db.query("port",
new String[] { "status", "id", "arrival",
"destination", "ferry" }, null, null,
null, null, null);
try {
if (c!=null) {
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext())
{
DBAdapter title = new DBAdapter(context);
title.status = c.getString(0);
title.id = c.getString(1);
title.arrival = c.getString(2);
title.destination = c.getString(3);
title.ferry = c.getString(4);
}
}
} finally {
if (c!=null) {
c.close();
}
}
return titles;
}//end getAllTitles()
}//end class DBAdapter
Upvotes: 0
Views: 441
Answers (1)
Chris Thompson
Reputation: 35598
You never call open() on your object. You are using a static call in your code, but that static call depends on nonstatic methods being called to set up the static data members. So when you call db.query() db is null, hence the null pointer exception. Your overall architecture is fundamentally flawed. You need to instantiate your DBAdapter object and call several methods such as open from within your static method. However, inside your static method, you are relying on the context object being set. However, you don't set that until you call the constructor. You need to make sure that your references are set before attempting to operate on them. I would suggest not attempting to make a static call like this unless you want to pass it a Context object. From there you will need to instantiate the DBAdapter object and call the appropriate setup methods (like open) before you can interact with the database.
Edit
Based on rereading your code, change your database adapter class to remove the static method:
package one.two;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.List;
import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import java.util.ArrayList;
public class DBAdapter extends ListActivity
{
private static String DB_PATH = "/data/data/one.two/databases/";
private static final String DATABASE_NAME = "ferry.db";
private static final String DATABASE_TABLE = "port";
public static Context context;
public String status = "status";
public String id = "id";
public String arrival = "arrival";
public String destination = "destination";
public String ferry = "ferry";
//null constructor
public DBAdapter()
{
}
//overloaded non-null constructor
public DBAdapter(Context context)
{
}
public class DatabaseHelper extends SQLiteOpenHelper
{
Context context;
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context = context;
}//end constructor DatabaseHelper
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
}//end onUpgrade()
@Override
public void onCreate(SQLiteDatabase db)
{
boolean dbExist = checkDatabase();
if (dbExist)
{
}
else
{
this.getReadableDatabase();
try
{
copyDataBase();
}
catch (IOException e)
{
throw new Error("Error copying database");
}
}
}//end onCreate()
}// end class DatabaseHelper
private static DatabaseHelper DBHelper;
private static SQLiteDatabase db;
private static final int DATABASE_VERSION = 1;
//// context brought up /////////////
//private final Context context;
private boolean checkDatabase()
{
SQLiteDatabase checkDB = null;
try
{
String myPath = DB_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}
catch (SQLiteException e)
{
// database doesn't exist yet
}
if (checkDB != null)
{
checkDB.close();
}
return checkDB != null ? true : false;
}//end checkDatabase()
private void copyDataBase() throws IOException
{
// Open your local db as the input stream
InputStream myInput = context.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DATABASE_NAME;
// Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
// transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0)
{
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}//end copyDataBase()
public void DBAdapter() throws SQLException
{
String myPath = DB_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
}//end DBAdapter()
public void open()
{
//Open the database
String myPath = DB_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
// ---closes the database---
public void close()
{
DBHelper.close();
}//end close()
public List<String> getAllTitles()
{
List<String> titles = new ArrayList<String>();
Cursor c=null;
c = db.query("port",
new String[] { "status", "id", "arrival",
"destination", "ferry" }, null, null,
null, null, null);
try {
if (c!=null) {
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext())
{
DBAdapter title = new DBAdapter(context);
title.status = c.getString(0);
title.id = c.getString(1);
title.arrival = c.getString(2);
title.destination = c.getString(3);
title.ferry = c.getString(4);
}
}
} finally {
if (c!=null) {
c.close();
}
}
return titles;
}//end getAllTitles()
}//end class DBAdapter
And change your Arrival class to use the nonstatic method:
package one.two;
import java.util.ArrayList;
import java.util.List;
import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class Arrival extends ListActivity
{
private ListView listView;
DBAdapter db = new DBAdapter(this);
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
getData();
// db.open();
listView = (ListView) findViewById(android.R.id.list);
// db.close();
}
private void getData()
{
// show some display that you are going to open db
db.open();
// show some display that you have opened
// redundant see below statement ---- List<String> items = new ArrayList<String>();
// call the DBAdapter method to getAllTitles()
List<String> items = db.getAllTitles();
// iterate through the items one by one thru display statement or show
// on layout
// check how to do that
ArrayAdapter<String> titles = new ArrayAdapter<String>(this,
R.layout.main, items);
db.close();
}
}
Upvotes: 2