您好， 我正在构建一个使用现有数据库的Android应用程序。但是，应用程序无法在我的设备上正常运行。
这是我的代码：
Mainactivity.java：
public class MainActivity extends TabActivity {
Cursor model = null;
TerrainAdapter adapter = null;
TextView nom = null;
TextView prenom = null;
TextView fonction = null;
terrainHelper helper = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
helper = new terrainHelper(this);
nom = (TextView) findViewById(R.id.nom);
prenom = (TextView) findViewById(R.id.prenom);
fonction = (TextView) findViewById(R.id.fonction);
ListView list = (ListView) findViewById(R.id.terrains);
model = helper.getAll();
startManagingCursor(model);
adapter = new TerrainAdapter(model);
list.setAdapter(adapter);
TabHost.TabSpec spec = getTabHost().newTabSpec("tag1");
spec.setContent(R.id.terrains);
spec.setIndicator("List", getResources().getDrawable(R.drawable.list));
getTabHost().addTab(spec);
spec = getTabHost().newTabSpec("tag2");
spec.setContent(R.id.details);
spec.setIndicator("Details", getResources().getDrawable(R.drawable.terrain));
getTabHost().addTab(spec);
getTabHost().setCurrentTab(0);
list.setOnItemClickListener(onListClick);
}
@Override
public void onDestroy() {
super.onDestroy();
helper.close();
}
private AdapterView.OnItemClickListener onListClick = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
model.moveToPosition(position);
nom.setText(helper.getNom(model));
prenom.setText(helper.getPrenom(model));
fonction.setText(helper.getFonction(model));
getTabHost().setCurrentTab(1);
}
};
class TerrainAdapter extends CursorAdapter {
TerrainAdapter(Cursor c) {
super(MainActivity.this, c);
}
@Override
public void bindView(View row, Context ctxt, Cursor c) {
TerrainHolder holder = (TerrainHolder) row.getTag();
holder.populateFrom(c, helper);
}
@Override
public View newView(Context ctxt, Cursor c, ViewGroup parent) {
LayoutInflater inflater = getLayoutInflater();
View row = inflater.inflate(R.layout.row, parent, false);
TerrainHolder holder = new TerrainHolder(row);
row.setTag(holder);
return (row);
}
}
static class TerrainHolder {
private TextView ville = null;
private TextView tache = null;
TerrainHolder(View row) {
ville = (TextView) row.findViewById(R.id.ville);
tache = (TextView) row.findViewById(R.id.tache);
}
void populateFrom(Cursor c, terrainHelper helper) {
ville.setText(helper.getNom(c));
tache.setText(helper.getFonction(c));
}
}
}
terrainHelper：
class terrainHelper extends SQLiteOpenHelper {
//Le path des bases du system Android (attention au nom du package de l'appli).
private static String DB_PATH = "/data/data/com.abouchan.docs/databases/";
//nom de la base
private static String DB_NAME = "db.sqlite3";
// la base
private SQLiteDatabase myDataBase;
// le context
private final Context myContext;
/**
* Constructeur
*
* @param context
*/
public terrainHelper(Context context) {
super(context, DB_NAME, null, 2);
this.myContext = context;
}
/**
* On cré une base vide dans le system Android et on réécris dessus.
* */
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
//On fait rien - La base existe déja.
} 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 {
//Copie de la base
copyDataBase();
} catch (IOException e) {
throw new Error("Erreur de copie de la base !");
}
}
}
/**
* On Check la base pour voir si elle existe ou pas
*
* @return true si la base existe, false si elle existe pas.
*/
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;
}
/* (non-Javadoc)
* @see android.database.sqlite.SQLiteOpenHelper#getReadableDatabase()
*/
@Override
public synchronized SQLiteDatabase getReadableDatabase() {
return super.getReadableDatabase();
}
/**
* On copie la base depuis le dossier assets dans le dossier system des bases sous android dans la base vide fraichement créé.
*
* */
private void copyDataBase() throws IOException {
//On ouvre la base locale
InputStream myInput = myContext.getAssets().open(DB_NAME);
// On choisi l'endroit
String outFileName = DB_PATH + DB_NAME;
//On ouvre la base vide
OutputStream myOutput = new FileOutputStream(outFileName);
//On transfert...
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
//On ferme ...
myOutput.flush();
myOutput.close();
myInput.close();
}
/**
*Fonction pour acceder à la base en mode lecture seul
**/
public void openDataBase() throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY | SQLiteDatabase.NO_LOCALIZED_COLLATORS);
}
@Override
public synchronized void close() {
if (myDataBase != null) {
myDataBase.close();
}
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
// On ne crées pas de base
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// pas de mis a jour
}
// developper vos methodes d'acces à la base que vous appelerez dans la Main ETC....
public Cursor getAll() {
return (myDataBase.rawQuery("SELECT nom, prenom, fonction FROM terrain ORDER BY nom ASC", null));
}
public String getNom(Cursor c) {
return (c.getString(1));
}
public String getPrenom(Cursor c) {
return (c.getString(2));
}
public String getFonction(Cursor c) {
return (c.getString(3));
}
}
这是我的logCat：
ERROR AndroidRuntime FATAL EXCEPTION: main
ERROR AndroidRuntime java.lang.RuntimeException: Unable to start activity ComponentInfo{com.abouchan.docs/com.abouchan.docs.MainActivity}: java.lang.NullPointerException
ERROR AndroidRuntime at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1664)
ERROR AndroidRuntime at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1680)
ERROR AndroidRuntime at android.app.ActivityThread.access$1500(ActivityThread.java:117)
ERROR AndroidRuntime at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
ERROR AndroidRuntime at android.os.Handler.dispatchMessage(Handler.java:99)
ERROR AndroidRuntime at android.os.Looper.loop(Looper.java:130)
ERROR AndroidRuntime at android.app.ActivityThread.main(ActivityThread.java:3703)
ERROR AndroidRuntime at java.lang.reflect.Method.invokeNative(Native Method)
ERROR AndroidRuntime at java.lang.reflect.Method.invoke(Method.java:507)
ERROR AndroidRuntime at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
ERROR AndroidRuntime at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
ERROR AndroidRuntime at dalvik.system.NativeStart.main(Native Method)
ERROR AndroidRuntime Caused by: java.lang.NullPointerException
ERROR AndroidRuntime at com.abouchan.docs.terrainHelper.getAll(terrainHelper.java:166)
ERROR AndroidRuntime at com.abouchan.docs.MainActivity.onCreate(MainActivity.java:54)
ERROR AndroidRuntime at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
ERROR AndroidRuntime at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1628)
ERROR AndroidRuntime ... 11 more
答案 0 :(得分：0)
这是你第一次运行吗？
似乎很简单的事实是您的活动可能未在Manifest.xml中声明
<activity android:name=".MainActivity"></activity>
<activity android:name=".TabActivity"></activity>
至少你需要这样的东西。
希望有所帮助！