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一直在使用外部創建的數據庫（一個包含109,000條記錄，大小爲6.307MB的單詞表），這讓我頭痛不已。我需要幫助找出這裏出了什麼問題。任何答案將不勝感激。在Android應用程序中使用外部sqlite數據庫的問題
這是代碼：
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.os.Build;
import android.app.*;
import android.database.Cursor;
public class MainActivity extends Activity
{
private DatabaseHelper db;
private Cursor c;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String[] a = new String[100];
int i=0;
db.openDataBase();
c = db.getWords("sl");
db.close();
while(c.isAfterLast())
{
a[i++]=c.getString(c.getColumnIndex("WORD"));
c.moveToNext();
}
ListView l = (ListView)findViewById(R.id.listView1);
l.setAdapter(new ArrayAdapter(this,android.R.layout.simple_list_item_1,a));
}
}
這是輔助類
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.database.*;
import android.database.sqlite.*;
import android.content.*;
import android.app.*;
public class DatabaseHelper extends SQLiteOpenHelper
{
private static String DB_PATH = "/data/data/com.example.attempt/databases/";
// Data Base Name.
private static final String DATABASE_NAME = "dict.db";
// Data Base Version.
private static final int DATABASE_VERSION = 1;
// Table Names of Data Base.
static final String TABLE_Name1 = "WORDS";
public Context context;
static SQLiteDatabase sqliteDataBase;
public DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null ,DATABASE_VERSION);
this.context = context;
}
@Override
public void onCreate(SQLiteDatabase arg0)
{
}
//check if the database exists
public void createDataBase() throws IOException
{
boolean databaseExist = checkDataBase();
if(databaseExist)
{
// Do Nothing.
}
else
{
this.getWritableDatabase();
copyDataBase();
// TODO Auto-generated catch block
}
}// end if else dbExist
// end createDataBase().
public boolean checkDataBase()
{
File databaseFile = new File(DB_PATH + DATABASE_NAME);
return databaseFile.exists();
}
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 input file to the output file
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();
}
/**
* This method opens the data base connection.
* First it create the path up till data base of the device.
* Then create connection with data base.
*/
public void openDataBase() throws SQLException
{
//Open the database
try {
createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
String myPath = DB_PATH + DATABASE_NAME;
sqliteDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
/**
* This Method is used to close the data base connection.
*/
@Override
public synchronized void close()
{
if(sqliteDataBase != null)
sqliteDataBase.close();
super.close();
}
//declare methods to fetch data
public Cursor getWords(String cat)
{
return sqliteDataBase.query("WORDS",new String[]{"WORD"},"CAT="+"'"+cat+"'", null, null,null,null);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
這裏調試完畢後顯示的logcat的：
04-19 12:17:32.463: D/dalvikvm(4040): GC_FOR_ALLOC freed 58K, 10% free 3450K/3832K, paused 317ms, total 324ms
04-19 12:17:34.073: D/dalvikvm(4040): GC_FOR_ALLOC freed 3K, 10% free 3668K/4056K, paused 414ms, total 415ms
04-19 12:17:34.073: I/dalvikvm-heap(4040): Grow heap (frag case) to 6.307MB for 2536936-byte allocation
04-19 12:17:34.603: D/dalvikvm(4040): GC_FOR_ALLOC freed <1K, 6% free 6145K/6536K, paused 520ms, total 520ms
04-19 12:17:35.623: D/AndroidRuntime(4040): Shutting down VM
04-19 12:17:35.623: W/dalvikvm(4040): threadid=1: thread exiting with uncaught exception (group=0xb1a8bba8)
04-19 12:17:35.673: E/AndroidRuntime(4040): FATAL EXCEPTION: main
04-19 12:17:35.673: E/AndroidRuntime(4040): Process: com.example.lexicant, PID: 4040
04-19 12:17:35.673: E/AndroidRuntime(4040): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lexicant/com.example.lexicant.MainActivity}: java.lang.NullPointerException
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.os.Handler.dispatchMessage(Handler.java:102)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.os.Looper.loop(Looper.java:136)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-19 12:17:35.673: E/AndroidRuntime(4040): at java.lang.reflect.Method.invokeNative(Native Method)
04-19 12:17:35.673: E/AndroidRuntime(4040): at java.lang.reflect.Method.invoke(Method.java:515)
04-19 12:17:35.673: E/AndroidRuntime(4040): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-19 12:17:35.673: E/AndroidRuntime(4040): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-19 12:17:35.673: E/AndroidRuntime(4040): at dalvik.system.NativeStart.main(Native Method)
04-19 12:17:35.673: E/AndroidRuntime(4040): Caused by: java.lang.NullPointerException
04-19 12:17:35.673: E/AndroidRuntime(4040): at com.example.lexicant.MainActivity.onCreate(MainActivity.java:30)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.Activity.performCreate(Activity.java:5231)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-19 12:17:35.673: E/AndroidRuntime(4040): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-19 12:17:35.673: E/AndroidRuntime(4040): ... 11 more
04-19 12:19:09.363: I/Process(4040): Sending signal. PID: 4040 SIG: 9
04-19 12:25:08.663: D/dalvikvm(5842): GC_FOR_ALLOC freed 66K, 11% free 3450K/3836K, paused 242ms, total 247ms
04-19 12:25:09.283: D/dalvikvm(5842): GC_FOR_ALLOC freed 3K, 10% free 3668K/4060K, paused 42ms, total 43ms
04-19 12:25:09.283: I/dalvikvm-heap(5842): Grow heap (frag case) to 6.307MB for 2536936-byte allocation
04-19 12:25:09.353: D/dalvikvm(5842): GC_FOR_ALLOC freed <1K, 7% free 6145K/6540K, paused 58ms, total 58ms
04-19 12:25:09.763: D/AndroidRuntime(5842): Shutting down VM
04-19 12:25:09.773: W/dalvikvm(5842): threadid=1: thread exiting with uncaught exception (group=0xb1a8bba8)
04-19 12:25:09.843: E/AndroidRuntime(5842): FATAL EXCEPTION: main
04-19 12:25:09.843: E/AndroidRuntime(5842): Process: com.example.lexicant, PID: 5842
04-19 12:25:09.843: E/AndroidRuntime(5842): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lexicant/com.example.lexicant.MainActivity}: java.lang.NullPointerException
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.os.Handler.dispatchMessage(Handler.java:102)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.os.Looper.loop(Looper.java:136)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-19 12:25:09.843: E/AndroidRuntime(5842): at java.lang.reflect.Method.invokeNative(Native Method)
04-19 12:25:09.843: E/AndroidRuntime(5842): at java.lang.reflect.Method.invoke(Method.java:515)
04-19 12:25:09.843: E/AndroidRuntime(5842): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-19 12:25:09.843: E/AndroidRuntime(5842): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-19 12:25:09.843: E/AndroidRuntime(5842): at dalvik.system.NativeStart.main(Native Method)
04-19 12:25:09.843: E/AndroidRuntime(5842): Caused by: java.lang.NullPointerException
04-19 12:25:09.843: E/AndroidRuntime(5842): at com.example.lexicant.MainActivity.onCreate(MainActivity.java:30)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.Activity.performCreate(Activity.java:5231)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-19 12:25:09.843: E/AndroidRuntime(5842): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-19 12:25:09.843: E/AndroidRuntime(5842): ... 11 more
04-19 12:25:15.073: I/Process(5842): Sending signal. PID: 5842 SIG: 9