我已经在这里阅读了与我的问题相关的几乎所有主题，所以请不要说它是重复的或者之前已被质疑过。
我在Sqlite Expert Personal 3中创建了表和数据库。我将它复制到assets文件夹中。现在我想告诉android检查是否已经有数据库，从assets文件夹中复制数据库。所以我这样做：
datasource = new DataSource(this);
List<Prayer> prayers = datasource.findAllPrayers();
if (prayers.size == 0)
{
dbopenhelper.copyDataBase();
}
datasource.open();
这里应该检查表格中是否有任何行＆＃34;祈祷＆＃34;如果没有任何行，它应该复制数据库。但是当我运行程序时，我得到nullPointerException。
这是我的OpenHelper课程：
package org.bihe.database;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBOpenHelper extends SQLiteOpenHelper
{
public static final String LOGTAG = "PRAYERBOOK_APP";
//
private static Context context;
//
private static String DB_PATH;
//
public static final String DATABASE_NAME = "Prayers.db";
public static final int DATABASE_VERSION = 1;
// ***Tables***
public static final String TABLE_PRAYERTOPIC = "prayertopic";
public static final String TABLE_PRAYER = "prayer";
public static final String TABLE_FAVORITES = "favorites";
public static final String TABLE_PRAYEROFTOPIC = "prayeroftopic";
public static final String TABLE_FAVORITEPRAYERS = "favoriteprayers";
public static final String TABLE_AUDIOPRAYERS = "audioprayers";
// ***Table prayertopic columns***
public static final String COLUMN_PRAYERTOPIC_ID = "prayertopic_ID";
public static final String COLUMN_PRAYERTOPIC_NAME = "prayertopic_name";
// ***Table prayer columns***
public static final String COLUMN_PRAYER_ID = "prayer_ID";
public static final String COLUMN_PRAYER_NAME = "prayer_name";
public static final String COLUMN_PRAYER = "prayer";
// ***Table favorites columns***
public static final String COLUMN_FAVORITE_ID = "favorite_ID";
public static final String COLUMN_FAVORITE_NAME = "favorite_name";
// ***Table prayeroftopic columns***
public static final String COLUMN_PRAYEROFTOPIC_ID = "prayeroftopic_ID";
public static final String COLUMN_PRAYER_ID_POT = "prayer_ID";
public static final String COLUMN_PRAYERTOPIC_ID_POT = "prayertopic_ID";
// ***Table favoriteprayer columns***
public static final String COLUMN_FAVORITEPRAYER_ID = "favoriteprayer_ID";
public static final String COLUMN_FAVORITE_ID_FP = "favorite_ID";
public static final String COLUMN_PRAYER_ID_FP = "prayer_ID";
// ***Table auidioprayers***
public static final String COLUMN_AUDIOPRAYER_ID = "audioprayer_ID";
public static final String COLUMN_AUDIOPRAYER_NAME = "audioprayer_name";
public static final String COLUMN_AUDIOPRAYER_ADDRESS = "audioprayer_address";
// ***Creating Tables***
private static final String CREATE_PRAYER_TABLE = "CREATE TABLE "
+ TABLE_PRAYER + " (" + COLUMN_PRAYER_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_PRAYER_NAME
+ " TEXT, " + COLUMN_PRAYER + " TEXT " + ")";
//
private static final String CREATE_PRAYERTOPIC_TABLE = "CREATE TABLE "
+ TABLE_PRAYERTOPIC + " (" + COLUMN_PRAYERTOPIC_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_PRAYERTOPIC_NAME
+ " TEXT" + ")";
//
private static final String CREATE_PRAYEROFTOPIC_TABLE = "CREATE TABLE "
+ TABLE_PRAYEROFTOPIC + " (" + COLUMN_PRAYEROFTOPIC_ID
+ " INTEGER PRIMARY KEY AUTOINCREMENT, " + " FOREIGN KEY("
+ COLUMN_PRAYER_ID_POT + ") REFERENCES " + TABLE_PRAYER + "("
+ COLUMN_PRAYER_ID + ") ON UPDATE CASCADE ON DELETE CASCADE "
+ " FOREIGN KEY(" + COLUMN_PRAYERTOPIC_ID_POT + ") REFERENCES "
+ TABLE_PRAYERTOPIC + "(" + COLUMN_PRAYERTOPIC_ID
+ ") ON UPDATE CASCADE ON DELETE CASCADE " + ") ";
public DBOpenHelper(Context ctx)
{
super(ctx, DATABASE_NAME, null, DATABASE_VERSION);
context = ctx;
DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
}
//
public static void copyDataBase()
{
try
{
InputStream input = context.getAssets().open(DATABASE_NAME);
FileOutputStream output = new FileOutputStream(DB_PATH
+ DATABASE_NAME);
byte[] data = new byte[1024];
int buffer;
while ((buffer = input.read(data)) != -1)
{
output.write(data, 0, buffer);
}
output.flush();
output.close();
input.close();
} catch (IOException ex)
{
Log.e(LOGTAG, "Error in copying database...");
}
}
//
// ***--***
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(CREATE_PRAYER_TABLE);
Log.i(LOGTAG, "Table has been created");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
// db.execSQL("DROP TABLE IF EXISTS " + TABLE_PRAYER);
onCreate(db);
}
}
如果有人能告诉我我的代码有什么问题，我将非常感激。感谢提前
编辑：
02-21 20:06:17.346: E/Trace(4814): error opening trace file: No such file or directory (2)
02-21 20:06:17.896: I/PRAYERBOOK_APP(4814): Database opened
02-21 20:06:17.968: I/PRAYERBOOK_APP(4814): Database opened
02-21 20:06:18.278: D/libEGL(4814): loaded /system/lib/egl/libEGL_emulation.so
02-21 20:06:18.430: D/(4814): HostConnection::get() New Host Connection established 0x2a13b0b8, tid 4814
02-21 20:06:19.047: D/libEGL(4814): loaded /system/lib/egl/libGLESv1_CM_emulation.so
02-21 20:06:19.057: D/libEGL(4814): loaded /system/lib/egl/libGLESv2_emulation.so
02-21 20:06:20.127: W/EGL_emulation(4814): eglSurfaceAttrib not implemented
02-21 20:06:20.169: D/OpenGLRenderer(4814): Enabling debug mode 0
02-21 20:06:20.507: D/dalvikvm(4814): GC_CONCURRENT freed 84K, 7% free 2706K/2908K, paused 91ms+6ms, total 199ms
02-21 20:06:56.497: I/PRAYERBOOK_APP(4814): Database closed
02-21 20:06:57.127: D/dalvikvm(4814): GC_FOR_ALLOC freed 65K, 6% free 2992K/3180K, paused 35ms, total 52ms
02-21 20:06:57.137: I/dalvikvm-heap(4814): Grow heap (frag case) to 4.110MB for 1127536-byte allocation
02-21 20:06:57.217: D/dalvikvm(4814): GC_FOR_ALLOC freed 3K, 5% free 4090K/4284K, paused 77ms, total 77ms
02-21 20:06:57.347: D/dalvikvm(4814): GC_CONCURRENT freed 5K, 5% free 4086K/4284K, paused 27ms+32ms, total 134ms
02-21 20:06:57.457: D/AndroidRuntime(4814): Shutting down VM
02-21 20:06:57.457: W/dalvikvm(4814): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
02-21 20:06:57.477: E/AndroidRuntime(4814): FATAL EXCEPTION: main
02-21 20:06:57.477: E/AndroidRuntime(4814): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.bihe.prayerbookletapp/org.bihe.prayerbookletapp.ExpListActivity}: java.lang.NullPointerException
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.os.Handler.dispatchMessage(Handler.java:99)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.os.Looper.loop(Looper.java:137)
02-21 20:06:57.477: E/AndroidRuntime(4814): at android.app.ActivityThread.main(ActivityThread.java:5041)
02-21 20:06:57.477: E/AndroidRuntime(4814): at java.lang.reflect.Method.invokeNative(Native Method)
02-21 20:06:57.477: E/AndroidRuntime(4814): at java.lang.reflect.Method.invoke(Method.java:511)
02-21 20:06:57.477: E/AndroidRuntime(4814): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-21 20:06:57.477: E/AndroidRuntime(4814): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-21 20:06:57.477: E/AndroidRuntime(4814): at dalvik.system.NativeStart.main(Native Method)
02-21 20:06:57.477: E/AndroidRuntime(4814): Caused by: java.lang.NullPointerException
02-21 20:06:57.477: E/AndroidRuntime(4814): at org.bihe.database.DataSource.findAllPrayers(DataSource.java:163)
02-21 20:06:57.477: E/AndroidRuntime(4814): at org.bihe.prayerbookletapp.ExpListActivity.onCreate(ExpListActivity.java:65)
02-21 20:06:57.477: E/AndroidRuntime(4814): at
android.app.Activity.performCreate（Activity.java:5104） 02-21 20：06：57.477：E / AndroidRuntime（4814）：在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1080） 02-21 20：06：57.477：E / AndroidRuntime（4814）：在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2144） 02-21 20：06：57.477：E / AndroidRuntime（4814）：... 11更多
和这里：02-21 20：06：57.477：E / AndroidRuntime（4814）：at org.bihe.database.DataSource.findAllPrayers（DataSource.java:163）
它指的是Datasource类中的findAllPrayers（）方法：
Here is my findAllPrayers() method which is in datasource class:
public List<Prayer> findAllPrayers()
{
List<Prayer> prayerlist = new ArrayList<Prayer>();
//
Cursor cursor = database.query(DBOpenHelper.TABLE_PRAYER,
allPrayerColumns, null, null, null, null, null);
//
Log.i(LOGTAG, "Child Cursor returned " + cursor.getCount() + " row(s).");
if (cursor.getCount() > 0)
{
while (cursor.moveToNext())
{
Prayer p = new Prayer();
p.setPrayer_name(cursor.getString(cursor
.getColumnIndex(DBOpenHelper.COLUMN_PRAYER_NAME)));
p.setPrayer_ID(cursor.getLong(cursor
.getColumnIndex(DBOpenHelper.COLUMN_PRAYER_ID)));
p.setPrayer(cursor.getString(cursor
.getColumnIndex(DBOpenHelper.COLUMN_PRAYER)));
prayerlist.add(p);
}
}
return prayerlist;
}