助手类：
package com.deangrobler.myApp;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.*;
public class DataBaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.deangrobler.chumperoo/databases/";
private static String DB_NAME = "ChumperooDB.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database: " + e.getStackTrace());
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
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;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
//Queries the database
public Cursor queryDataBase(String table, String[] columns, String selection){
return myDataBase.query(table, columns, selection, null, null, null, null);
}
}
在我的 Main.java 中使用如下：
DataBaseHelper myDbHelper = new DataBaseHelper(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
//Get cursor and print out data
Cursor returnedCur = myDbHelper.queryDataBase("Expenses", new String[]{"Name","Amount"}, null);
if (returnedCur.moveToFirst()){
do{
String data = returnedCur.getString(returnedCur.getColumnIndex("data"));
System.out.println("Returned Data: "+data);
}while(returnedCur.moveToNext());
}
returnedCur.close();
最后我的整个日志：
> 06-05 13:28:35.885: E/CursorWindow(733): Bad request for field slot 0,-1. numRows = 1, numColumns = 2
06-05 13:28:35.885: D/AndroidRuntime(733): Shutting down VM
06-05 13:28:35.885: W/dalvikvm(733): threadid=1: thread exiting with uncaught exception (group=0x40015560)
06-05 13:28:35.904: E/AndroidRuntime(733): FATAL EXCEPTION: main
06-05 13:28:35.904: E/AndroidRuntime(733): **java.lang.RuntimeException: Unable to start activity ComponentInfo{com.deangrobler.chumperoo/com.deangrobler.chumperoo.Main}: java.lang.IllegalStateException: get field slot from row 0 col -1 failed**
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.os.Handler.dispatchMessage(Handler.java:99)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.os.Looper.loop(Looper.java:123)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread.main(ActivityThread.java:3647)
06-05 13:28:35.904: E/AndroidRuntime(733): at java.lang.reflect.Method.invokeNative(Native Method)
06-05 13:28:35.904: E/AndroidRuntime(733): at java.lang.reflect.Method.invoke(Method.java:507)
06-05 13:28:35.904: E/AndroidRuntime(733): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
06-05 13:28:35.904: E/AndroidRuntime(733): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
06-05 13:28:35.904: E/AndroidRuntime(733): at dalvik.system.NativeStart.main(Native Method)
06-05 13:28:35.904: E/AndroidRuntime(733): Caused by: java.lang.IllegalStateException: get field slot from row 0 col -1 failed
06-05 13:28:35.904: E/AndroidRuntime(733): at android.database.CursorWindow.getString_native(Native Method)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.database.CursorWindow.getString(CursorWindow.java:329)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:49)
06-05 13:28:35.904: E/AndroidRuntime(733): at com.deangrobler.chumperoo.Main.onCreate(Main.java:55)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-05 13:28:35.904: E/AndroidRuntime(733): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586)
06-05 13:28:35.904: E/AndroidRuntime(733): ... 11 more
06-05 13:28:53.264: I/Process(733): Sending signal. PID: 733 SIG: 9
不知道为什么会这样，我已经用谷歌搜索了半天了，没有什么能帮助我解决这个问题:-(