java - 首次启动 Android 时应用程序崩溃

Question

我有一个应用程序，它从 sqlite 数据库浏览器读取数据库，然后复制数据库并继续。然而，每次我在 sqlite 数据库浏览器中更改数据库时，我都必须卸载并重新安装应用程序才能再次复制它。 (这仅适用于大学作业)在第一次启动时它总是崩溃，但在第二次启动时却可以工作。有办法避免这种崩溃吗？

这是我的一些代码:

 public DbH(Context context) throws IOException {
    super(context, DB_NAME, null, 1);
    this.mycontext = context;
}

public void createdatabase() throws IOException {
    boolean dbexist = checkdatabase();
    if (dbexist) {
        System.out.println(" Database exists.");
    } else {
        this.getReadableDatabase();
        try {
            copydatabase();
        } catch (IOException e) {
            throw new Error("Error copying database");
        }
    }
}

private boolean checkdatabase() {
    // SQLiteDatabase checkdb = null;
    boolean checkdb = false;
    try {
        String myPath = DB_PATH + DB_NAME;
        File dbfile = new File(myPath);
        checkdb = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE) != null;
        checkdb = dbfile.exists();
    } catch (SQLiteException e) {
        System.out.println("Database doesn't exist");
    }

    return checkdb;
}

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);

}

public synchronized void close() {
    if (myDataBase != null) {
        myDataBase.close();
    }
    super.close();

} 

这是 Logcat 中的错误

    04-01 22:24:55.909: E/SqliteDatabaseCpp(25335): DB info: sqlite3_open_v2("/data/data/com.example.databasebrowser/databases , key = T", &handle, 2,     NULL) failed
    04-01 22:24:55.909: E/SqliteDatabaseCpp(25335): DB info: errno = 2, errno message = No such file or directory
    04-01 22:24:55.949: E/SQLiteDatabase(25335): Failed to open the database. closing it.
    04-01 22:24:55.949: E/SQLiteDatabase(25335): android.database.sqlite.SQLiteCantOpenDatabaseException: unable to open database file
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.dbopen(Native Method)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1093)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1050)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1026)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.example.databasebrowser.DbH.checkdatabase(DbH.java:60)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.example.databasebrowser.DbH.createdatabase(DbH.java:41)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.example.databasebrowser.MyActivity.validateLogin(MyActivity.java:99)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.example.databasebrowser.MyActivity.onClick(MyActivity.java:66)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.view.View.performClick(View.java:3538)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.view.View$PerformClick.run(View.java:14330)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.os.Handler.handleCallback(Handler.java:608)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.os.Handler.dispatchMessage(Handler.java:92)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.os.Looper.loop(Looper.java:156)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at android.app.ActivityThread.main(ActivityThread.java:4977)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at java.lang.reflect.Method.invokeNative(Native Method)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at java.lang.reflect.Method.invoke(Method.java:511)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
    04-01 22:24:55.949: E/SQLiteDatabase(25335):    at dalvik.system.NativeStart.main(Native Method)
    04-01 22:24:56.450: E/SqliteDatabaseCpp(25335): SELECT locale FROM android_metadata failed
    04-01 22:24:56.470: E/SQLiteDatabase(25335): Failed to open the database. closing it.
    04-01 22:24:56.470: E/SQLiteDatabase(25335): android.database.sqlite.SQLiteException: no such table: android_metadata
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:2186)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1094)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1050)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1026)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at com.example.databasebrowser.DbH.opendatabase(DbH.java:98)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at com.example.databasebrowser.MyActivity.validateLogin(MyActivity.java:105)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at com.example.databasebrowser.MyActivity.onClick(MyActivity.java:66)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.view.View.performClick(View.java:3538)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.view.View$PerformClick.run(View.java:14330)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.os.Handler.handleCallback(Handler.java:608)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.os.Handler.dispatchMessage(Handler.java:92)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.os.Looper.loop(Looper.java:156)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at android.app.ActivityThread.main(ActivityThread.java:4977)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at java.lang.reflect.Method.invokeNative(Native Method)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at java.lang.reflect.Method.invoke(Method.java:511)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
    04-01 22:24:56.470: E/SQLiteDatabase(25335):    at dalvik.system.NativeStart.main(Native Method)
    04-01 22:24:56.480: E/AndroidRuntime(25335): FATAL EXCEPTION: main
    04-01 22:24:56.480: E/AndroidRuntime(25335): android.database.sqlite.SQLiteException: no such table: android_metadata
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:2186)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1094)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1050)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:1026)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at com.example.databasebrowser.DbH.opendatabase(DbH.java:98)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at com.example.databasebrowser.MyActivity.validateLogin(MyActivity.java:105)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at com.example.databasebrowser.MyActivity.onClick(MyActivity.java:66)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.view.View.performClick(View.java:3538)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.view.View$PerformClick.run(View.java:14330)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.os.Handler.handleCallback(Handler.java:608)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.os.Handler.dispatchMessage(Handler.java:92)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.os.Looper.loop(Looper.java:156)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at android.app.ActivityThread.main(ActivityThread.java:4977)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at java.lang.reflect.Method.invokeNative(Native Method)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at java.lang.reflect.Method.invoke(Method.java:511)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
    04-01 22:24:56.480: E/AndroidRuntime(25335):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

你应该子类化 SQLiteOpenHelper以避免数据库创建错误。这可以处理所有数据库创建、更新和检查是否存在问题 - 无需您自己执行。此外，它还会在默认推荐路径中创建数据库文件。

以下可以是您可以在代码中使用的数据库打开帮助程序类。

class myDbHelper extends SQLiteOpenHelper {
    public myDbHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }

    // Called when no database exists on disk 
    @Override
    public void onCreate(SQLiteDatabase _db) {
        _db.execSQL(DATABASE_CREATE);
    }

    // Called when there is a database version mismatch meaning that
    // the version of the database on disk needs to be upgraded to
    // the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion,
            int _newVersion) {
        // Upgrade the existing database to conform to the new version.
        _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
        // Create a new one.
        onCreate(_db);
    }
}

拉尔斯·沃格尔有一个 nice tutorial关于这一点。