我正在 Android 中做一个项目,我正在尝试将现有数据库加载到我的应用程序中。我遇到了一个错误。
public class DBHelper extends SQLiteOpenHelper{
private static String DB_PATH = "/data/data/com.example.qbox/databases/";
private static String DB_NAME = "frases.db";
private SQLiteDatabase myDatabase;
private final Context _context;
public static final String KEY_ID = "_id";
public final static String KEY_FRASE = "frase";
public final static String KEY_AUTOR = "autor";
public final static String KEY_CATEGORIA = "categoria";
public final static String KEY_FAVORITA = "favorita";
public static final String DATABASE_TABLE = "frases";
private static final String[] cols = new String[] { KEY_ID, KEY_FRASE, KEY_AUTOR, KEY_CATEGORIA, KEY_FAVORITA};
public DBHelper(Context context) {
super(context, DB_NAME, null, 1);
this._context = context;
}
/**
* create new db and then rewrite records.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
// dn exists ... nothing to do
} else {
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copiando Base de Datos");
}
}
}
/**
* Check if db exists
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch(SQLiteException e) {
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copy Database
**/
private void copyDataBase() throws IOException{
InputStream myInput = _context.getAssets().open(DB_NAME);
String outFileName = DB_PATH + DB_NAME;
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while (( length = myInput.read(buffer)) > 0){
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
public void open() throws SQLException{
try {
createDataBase();
} catch (IOException e) {
throw new Error("Ha sido imposible crear la Base de Datos");
}
String myPath = DB_PATH + DB_NAME;
myDatabase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@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) {
}
/**
* INSERTAR NUEVA FRASE
* */
public long insertarFrase(Integer id,String frase, String autor, String categoria, String favorita ) {
ContentValues newValues = new ContentValues();
newValues.put(KEY_ID, id);
newValues.put(KEY_FRASE,frase);
newValues.put(KEY_AUTOR, autor);
newValues.put(KEY_CATEGORIA, categoria);
newValues.put(KEY_FAVORITA, favorita);
return myDatabase.insert(DATABASE_TABLE, null, newValues);
}
/**
* BORRAR FRASE CON _id = _rowIndex
* */
public boolean removerFrase(long _rowIndex) {
return myDatabase.delete(DATABASE_TABLE, KEY_ID + "=" + _rowIndex, null) > 0;
}
/**
* ACTUALIZAR FRASE _id = _rowIndex
* */
public boolean updateFrase(Integer _rowIndex, String frase, String autor, String categoria, String favorita ) {
ContentValues newValues = new ContentValues();
newValues.put(KEY_FRASE,frase);
newValues.put(KEY_AUTOR, autor);
newValues.put(KEY_CATEGORIA, categoria);
newValues.put(KEY_FAVORITA, favorita);
return myDatabase.update(DATABASE_TABLE, newValues, KEY_ID + "=" + _rowIndex, null) > 0;
}
public List<Frase> getTodasLasFrases() {
List<Frase> contacts = new ArrayList<Frase>();
Cursor cursor = myDatabase.query(DBHelper.DATABASE_TABLE,
cols, null, null, null, null, null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
Frase frase = cursorFrase(cursor);
contacts.add(frase);
cursor.moveToNext();
}
cursor.close();
return contacts;
}
private Frase cursorFrase(Cursor cursor) {
Frase frase = new Frase();
frase.setId(cursor.getLong(0));
frase.setFrase(cursor.getString(1));
frase.setAutor(cursor.getString(2));
frase.setCat(cursor.getString(3));
frase.setFav(cursor.getString(4));
return frase;
}
public Frase getContact(int id) {
Cursor cursor = myDatabase.query(DBHelper.DATABASE_TABLE, cols, this.KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Frase frase = cursorFrase(cursor);
return frase;
}
}
在主班
公共类 Home 扩展 Activity 实现 OnClickListener {
ImageButton favBtn,catBtn,infoBtn,shareBtn;
DBHelper db;
ListView lv;
List<Frase> values;
ArrayAdapter<Frase> adapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
favBtn =(ImageButton) findViewById(R.id.favBtn);
catBtn = (ImageButton) findViewById(R.id.catBtn);
infoBtn = (ImageButton) findViewById(R.id.infoBtn);
shareBtn = (ImageButton) findViewById(R.id.shareBtn);
infoBtn.setOnClickListener(this);
catBtn.setOnClickListener(this);
favBtn.setOnClickListener(this);
shareBtn.setOnClickListener(this);
prepararFrases();
}
@Override
public void onClick(View v) {
}
public void prepararFrases(){
db.open();
/*
values = db.getTodasLasFrases();
adapter = new ArrayAdapter<Frase>(this,
android.R.layout.simple_list_item_1, values);
//setListAdapter(adapter);
for (Frase cn : values) {
String log = "Id: "+cn.getId()+" ,Frase: " + cn.getFrase()+ " ,Autor: " + cn.getAutor();
Log.d("Name: ", log);
}
db.close();*/
}
}
错误:
11-10 21:45:08.366: E/AndroidRuntime(5535): Uncaught handler: thread main exiting due to uncaught exception
11-10 21:45:08.376: E/AndroidRuntime(5535): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.qbox/com.example.quotebox.Home}: java.lang.NullPointerException
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2503)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2519)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread.access$2200(ActivityThread.java:123)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1870)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.os.Handler.dispatchMessage(Handler.java:99)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.os.Looper.loop(Looper.java:123)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread.main(ActivityThread.java:4370)
11-10 21:45:08.376: E/AndroidRuntime(5535): at java.lang.reflect.Method.invokeNative(Native Method)
11-10 21:45:08.376: E/AndroidRuntime(5535): at java.lang.reflect.Method.invoke(Method.java:521)
11-10 21:45:08.376: E/AndroidRuntime(5535): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-10 21:45:08.376: E/AndroidRuntime(5535): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
11-10 21:45:08.376: E/AndroidRuntime(5535): at dalvik.system.NativeStart.main(Native Method)
11-10 21:45:08.376: E/AndroidRuntime(5535): Caused by: java.lang.NullPointerException
11-10 21:45:08.376: E/AndroidRuntime(5535): at com.example.qbox.Home.prepararFrases(Home.java:74)
11-10 21:45:08.376: E/AndroidRuntime(5535): at com.example.qbox.Home.onCreate(Home.java:45)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-10 21:45:08.376: E/AndroidRuntime(5535): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2466)
11-10 21:45:08.376: E/AndroidRuntime(5535): ... 11 more