Question

Hy Guys！

我的问题是Android向我显示一个错误，表示我没有默认的构造函数类。 AndroidManifest中出现错误。

这是我的代码：

package at.atn.android;

import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.content.Context;
import android.database.sqlite.SQLiteException;
import android.database.SQLException;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileOutputStream;

public class DatabaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/at.atn.android/databases/";

public static String DB_NAME = "db.sqlite3";

private SQLiteDatabase myDataBase;

private final Context myContext;


@Override
public void onCreate(SQLiteDatabase db) {
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

/**
 * Constructor
 * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
 *
 * @param context
 */
public DatabaseHelper(Context context) {

    super(context, DB_NAME, null, 1);
    this.myContext = context;
}

/**
 * Creates a empty database on the system and rewrites it with your own database.
 */
public void createDataBase() throws IOException {

    boolean dbExist = checkDataBase();

    if (dbExist) {
        //do nothing - database already exist
    } 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 {

            copyDataBase();

        } catch (IOException e) {

            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
 */
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;
}

/**
 * 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 = myContext.getAssets().open(DB_NAME);

    // Path to the just created empty db
    String outFileName = DB_PATH + DB_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();

}

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();

}

// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.

}

Android Manifest：

<application
    android:allowBackup="true"
    android:icon="@drawable/bus"
    android:label="@string/app_name"
    android:theme="@android:style/Theme.Light.NoTitleBar.Fullscreen" >
    <activity
        android:name="at.atn.android.MainActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name="at.atn.android.PlanActivity"></activity>
    <activity android:name="at.atn.android.InfoActivity"></activity>
    <activity android:name="at.atn.android.PlanAusgabeSubActivity"></activity>
    <activity android:name="at.atn.android.SetzeZeitActivity"></activity>
    <activity android:name="at.atn.android.ListHaltestelleActivity"/>
    <activity android:name="at.atn.android.AktualisiereDB"></activity>
    <activity android:name="at.atn.android.DatabaseHelper"></activity>
</application>

感谢您的帮助！

Answer 1

您只应在清单中声明activity的活动。 DatabaseHelper不是活动，不需要在清单中声明。 AktualisiereDB看起来也很可疑。

只需从清单中删除非活动活动。

DatabaseManager没有默认构造函数

1 个答案: