[英]NullPointerException in ContextWrapper.openOrCreateDatabase when using SQLiteOpenHelper
我正在制作一個使用數據庫的新android應用程序。 我使用了類似的代碼來創建和復制數據庫,但是由於某種原因,它無法正常工作。 我不知道,幫助。 logcat的:
07-03 21:38:54.260: E/AndroidRuntime(12172): FATAL EXCEPTION: main
07-03 21:38:54.260: E/AndroidRuntime(12172): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{lv.revopeng.guessthelocation/lv.revopeng.guessthelocation.LevelActivity}: java.lang.NullPointerException
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.os.Handler.dispatchMessage(Handler.java:99)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.os.Looper.loop(Looper.java:123)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread.main(ActivityThread.java:4627)
07-03 21:38:54.260: E/AndroidRuntime(12172): at java.lang.reflect.Method.invokeNative(Native Method)
07-03 21:38:54.260: E/AndroidRuntime(12172): at java.lang.reflect.Method.invoke(Method.java:521)
07-03 21:38:54.260: E/AndroidRuntime(12172): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-03 21:38:54.260: E/AndroidRuntime(12172): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-03 21:38:54.260: E/AndroidRuntime(12172): at dalvik.system.NativeStart.main(Native Method)
07-03 21:38:54.260: E/AndroidRuntime(12172): Caused by: java.lang.NullPointerException
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:112)
07-03 21:38:54.260: E/AndroidRuntime(12172): at lv.revopeng.guessthelocation.DataBaseHelper.open(DataBaseHelper.java:114)
07-03 21:38:54.260: E/AndroidRuntime(12172): at lv.revopeng.guessthelocation.DataBaseHelper.getLastId(DataBaseHelper.java:128)
07-03 21:38:54.260: E/AndroidRuntime(12172): at lv.revopeng.guessthelocation.LevelActivity.<init>(LevelActivity.java:31)
07-03 21:38:54.260: E/AndroidRuntime(12172): at java.lang.Class.newInstanceImpl(Native Method)
07-03 21:38:54.260: E/AndroidRuntime(12172): at java.lang.Class.newInstance(Class.java:1429)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
07-03 21:38:54.260: E/AndroidRuntime(12172): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
07-03 21:38:54.260: E/AndroidRuntime(12172): ... 11 more
DataBaseHelper.java:
public class DataBaseHelper extends SQLiteOpenHelper {
// The Android's default system path of your application database.
private static String DB_PATH = "/data/data/lv.revopeng.guessthelocation/databases/";
private static String DB_NAME = "GuessTheLocationTest.db";
public static final String TABLE_NAME1 = "gtl_levels";
public static final String WHATTODONOW_COLUMN_ID = "_id";
public static final String WHATTODONOW_COLUMN_INFO = "levelInfo";
public static final String WHATTODONOW_COLUMN_ANSWER = "levelAnswer";
public static final String WHATTODONOW_COLUMN_IMAGE = "levelImage";
public static final String WHATTODONOW_COLUMN_CLEARED = "levelCleared";
private DataBaseHelper openHelper;
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();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
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;
}
private void copyDataBase() throws IOException {
InputStream myInput = myContext.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 openDataBase() throws SQLException {
// Open the database
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 myDataBase, int oldVersion,
int newVersion) {
}
public DataBaseHelper open() throws SQLException {
openHelper = new DataBaseHelper(myContext);
myDataBase = openHelper.getWritableDatabase();
return this;
}
public void closee() {
openHelper.close();
}
String[] columns = new String[] { WHATTODONOW_COLUMN_ID,
WHATTODONOW_COLUMN_INFO, WHATTODONOW_COLUMN_ANSWER,
WHATTODONOW_COLUMN_IMAGE, WHATTODONOW_COLUMN_CLEARED };
public int getLastId() {
int id = 0;
open();
final String MY_QUERY = "SELECT MAX(_id) AS _id FROM " + TABLE_NAME1;
Cursor mCursor = myDataBase.rawQuery(MY_QUERY, null);
try {
if (mCursor.getCount() > 0) {
mCursor.moveToFirst();
id = mCursor.getInt(0);
mCursor.close();
close();
}
} catch (Exception e) {
System.out.println(e.getMessage());
} finally {
}
return id;
}
在LevelActivity.java上,將調用createDataBase()方法,並且在首次使用DataBaseHelper時,它將獲得錯誤。
編輯:對我來說,看起來getLastId為null,但不應這樣,因此訪問數據庫時出現問題。 我查看了文件資源管理器,數據庫在那里,並且其中的信息是正確的。
發現我的錯誤。 我調用了一個函數,該函數在創建數據庫之前從數據庫獲取數據。
刪除open()
方法。
不要調用getReadableDatabase();
和/或getWritableDatabase();
而是直接在DataBaseHelper.java中使用數據庫(即,使用execSQL()
, query()
, insert()
等)。 在其他地方使用這些方法作為dataBaseHelper.getReadableDatabase();
, dataBaseHelper.getWritableDatabase();
。
刪除DB_PATH
,不要使用一個。 您不需要提供路徑,系統將從您的packages數據庫文件夾中創建並讀取數據庫。
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