我刚刚开始为Android开发。我在实现SQLite数据库时遇到了一些问题。我使用从assests复制的现有数据库。这是我的代码：
public class CarsDB {
private static final int VERSION_BDD = 1;
private static final String NOM_BDD = "cars.db";
private static final String TABLE = "Models";
private static final String COL_ID = "_id";
private static final int NUM_COL_ID = 2;
private static final String COL_MODEL = "Model";
private static final int NUM_COL_MODEL = 0;
private static final String COL_CONSO = "Conso";
private static final int NUM_COL_CONSO = 1;
private Context context;
private SQLiteDatabase db;
private DataBaseHelper SQLite;
public CarsDB(Context context){
this.context=context;
//SQLite = new DataBaseHelper(context);
}
public CarsDB open() throws SQLException{
SQLite=new DataBaseHelper(context);
//SQLite.close();
db = SQLite.getWritableDatabase();
return this;
}
public void close(){
SQLite.close();
}
public SQLiteDatabase getBDD(){
return db;
}
public Cursor getCarWithModel(String Model){
String loadFav = "SELECT * FROM Models where Model LIKE'"+Model+"%'";
//Cursor c = db.query(TABLE, null,"Model LIKE'"+Model+"%'" , null, null, null, null);
Cursor c = db.rawQuery(loadFav, null);
return c;
//return cursorToCar(c);
}
这是我的OpenHelper：
public class DataBaseHelper extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/com.fresh.watch/databases/";
private static String DB_NAME = "cars.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
public DataBaseHelper(Context context){
super(context, DB_NAME,null,1);
this.myContext=context;
}
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
}else{
this.getReadableDatabase();
this.close();
try {
copyDataBase();
} catch (IOException e) {
// TODO: handle exception
throw new Error("Error copying database");
}
}
}
private boolean checkDataBase() {
// TODO Auto-generated method stub
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
//String myPath = Environment.getExternalStorageDirectory()+"/" + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
// TODO: handle exception
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null? true : false;
}
private void copyDataBase() throws IOException{
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
//String outFileName = Environment.getExternalStorageDirectory()+"/" + DB_NAME;
String outFileName = DB_PATH + DB_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();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
//String myPath = Environment.getExternalStorageDirectory()+"/" + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
堆栈追踪：
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): FATAL EXCEPTION: main
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fresh.watch/com.fresh.watch.Carmodels}: java.lang.NullPointerException
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread.access$1500(ActivityThread.java:123)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.os.Handler.dispatchMessage(Handler.java:99)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.os.Looper.loop(Looper.java:123)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread.main(ActivityThread.java:3835)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at java.lang.reflect.Method.invokeNative(Native Method)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at java.lang.reflect.Method.invoke(Method.java:507)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at dalvik.system.NativeStart.main(Native Method)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): Caused by: java.lang.NullPointerException
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at com.fresh.watch.CarsDB.getCarWithModel(CarsDB.java:76)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at com.fresh.watch.Carmodels.onCreate(Carmodels.java:28)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-04 03:27:46.154: ERROR/AndroidRuntime(23348): ... 11 more