我正在尝试从我的资源文件夹中访问SQLite数据库中的数据。数据库的名称是“fruits.sql”。
第一：
public class ArticlesTable {
public String TABLE_NAME="fruit";
public String ORANGE="orange";
}
然后我的模态
public class Article {
public String orange;
}
最后我的DBHelper类是
public class DBHelper {
private final String DATABASE_PATH = "/data/data/mon.immeuble/databases/";
private final String DATABASE_NAME = "frui.sqlite";
private final static int DATABASE_VERSION = 1;
private Context context;
private SQLiteDatabase database = null;
OpenHelper openHelper=null;
StringBuilder query =null;
Cursor cursor=null;
ArticlesTable articlesTable=new ArticlesTable();
public static DBHelper dbHelper = null;
private DBHelper(Context context) {
this.context = context;
openHelper = new OpenHelper(this.context);
this.database = openHelper.getWritableDatabase();
try {
createDataBase();
openDataBase();
} catch (IOException e) {
e.printStackTrace();
}
}
public static DBHelper getInstance(Context context)
{
if(dbHelper == null)
dbHelper = new DBHelper(context);
return dbHelper;
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DATABASE_PATH + DATABASE_NAME;
database = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException
{
openHelper.getReadableDatabase();
if(getDBAlreadyCopiedToDeviceOnceFlag(context) == false){
try {
copyDataBase();
setDBAlreadyCopiedToDeviceOnceFlag(context);
} catch (IOException e) {
e.printStackTrace();
throw new Error("Error copying database");
}
}
}
/**
* 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
*/
@SuppressWarnings("unused")
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DATABASE_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}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 = context.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DATABASE_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();
}
private class OpenHelper extends SQLiteOpenHelper
{
@SuppressWarnings("unused")
SQLiteStatement insertStmt;
public OpenHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
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 void setDBAlreadyCopiedToDeviceOnceFlag(Context ctx)
{
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(ctx);
SharedPreferences.Editor editor = prefs.edit();
editor.putBoolean("isDBAlreadyCopiedToDeviceOnce", true);
editor.commit();
}
public boolean getDBAlreadyCopiedToDeviceOnceFlag(Context ctx)
{
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(ctx);
boolean isDBAlreadyCopiedToDeviceOnce = prefs.getBoolean("isDBAlreadyCopiedToDeviceOnce", false);
return isDBAlreadyCopiedToDeviceOnce;
}
public ArrayList<Article> getArticlesList()
{
ArrayList<Article> items=new ArrayList<Article>();
try
{
query = new StringBuilder();
query.append("select * from "+articlesTable.TABLE_NAME+" ORDER BY nom DESC");
cursor=this.database.rawQuery(query.toString(),null);
if (cursor.moveToFirst())
{
do
{
Article a=new Article();
a.orange=cursor.getString(cursor.getColumnIndex(articlesTable.FRUIT));
items.add(a);
System.out.println("added_items:"+items);
}
while (cursor.moveToNext());
}
if (cursor != null && !cursor.isClosed())
{
cursor.close();
}
}
catch(SQLiteException e){
e.printStackTrace();
return null;
}
return items;
}
//--here
public boolean addArticle(Article a){
this.database.beginTransaction();
try{
ContentValues contentValues=new ContentValues();
contentValues.put(articlesTable.FRUIT, a.fruit);
this.database.insert(articlesTable.TABLE_NAME,null,contentValues);
this.database.setTransactionSuccessful();
}catch(Exception e){
e.printStackTrace();
return false;
}finally{
this.database.endTransaction();
}
return true;
}
和我访问数据的全局类
public class Globals {
public static DBHelper dbHelper;
public static ArrayList<Article> articles;
public static void copyArticles(ArrayList<Article> articlesList) {
if(articlesList!=null){
if(articles==null)
articles=new ArrayList<Article>();
else
articles.clear();
for(Article a: articlesList)
articles.add(a);
}
}
但是，当我使用
在我的创建活动中调用一个字段时 public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fruit);
System.out.println(Globals.articles.get(0).adresse1);
}
我得到一个空指针异常。
更新
Alex G.解决了这个问题，现在我在日志中收到此错误
04-22 13:43:52.375: E/AndroidRuntime(5015): FATAL EXCEPTION: main
04-22 13:43:52.375: E/AndroidRuntime(5015): java.lang.Error: Error copying database
04-22 13:43:52.375: E/AndroidRuntime(5015): at .db.DBHelper.createDataBase(DBHelper.java:82)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .db.DBHelper.<init>(DBHelper.java:47)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .db.DBHelper.getInstance(DBHelper.java:59)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .utils.Globals.init(Globals.java:17)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .utils.map.Map.onCreate(Map.java:71)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.startActivityNow(ActivityThread.java:1491)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:657)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.widget.TabHost.setCurrentTab(TabHost.java:329)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .TabSample.setProximite(TabSample.java:567)
04-22 13:43:52.375: E/AndroidRuntime(5015): at .TabSample.onCreate(TabSample.java:81)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.os.Handler.dispatchMessage(Handler.java:99)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.os.Looper.loop(Looper.java:130)
04-22 13:43:52.375: E/AndroidRuntime(5015): at android.app.ActivityThread.main(ActivityThread.java:3687)
04-22 13:43:52.375: E/AndroidRuntime(5015): at java.lang.reflect.Method.invokeNative(Native Method)
04-22 13:43:52.375: E/AndroidRuntime(5015): at java.lang.reflect.Method.invoke(Method.java:507)
04-22 13:43:52.375: E/AndroidRuntime(5015): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
04-22 13:43:52.375: E/AndroidRuntime(5015): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
04-22 13:43:52.375: E/AndroidRuntime(5015): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：2)
您正在尝试从ArrayList articles获取一个项目，但您没有在任何地方初始化它。如果没有评论你的类结构，你至少需要初始化你的dbhelper和你的arraylist：
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fruit);
Globals.init(this);
System.out.println(Globals.articles.get(0).adresse1);
}
请注意添加对init的调用。然后：
public class Globals {
public static DBHelper dbHelper;
public static ArrayList<Article> articles;
public static void init(Context ctx) {
DBHelper helper = DBHelper.getInstance(ctx);
copyArticles(helper.getArticlesList());
}
public static void copyArticles(ArrayList<Article> articlesList) {
if(articlesList!=null){
if(articles==null)
articles=new ArrayList<Article>();
else
articles.clear();
for(Article a: articlesList)
articles.add(a);
}
}
}
同样，我没有对您的代码的结构方式做出任何评论，只是简单地指出了您收到错误的原因。