android - 使用我的 DBhelper 类插入和删除值

Question

我找到了一个 dbhelper 类，它将我之前创建的数据库复制到 DB_PATH = "/data/data/"+ context.getPackageName() + "/"+ "databases_name/" 通过这个对象，我可以很容易地从我复制的数据库中读取数据。但是，我不知道如何从该数据库中插入和删除数据。

这是我完整的 dbhelper 对象..

public class DatabaseHelper extends SQLiteOpenHelper {

// The Android's default system path of your application database.
String DB_PATH = null;

private static String DB_NAME = "ContactInfo";

private SQLiteDatabase myDataBase;

private final Context myContext;

/**
 * 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;
    DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
}

/**
 * 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_READWRITE);


}

@Override
public synchronized void close() {

    if (myDataBase != null)
        myDataBase.close();

    super.close();

}

@Override
public void onCreate(SQLiteDatabase arg0) {
    // TODO Auto-generated method stub

}

@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
    // TODO Auto-generated method stub

}

// return cursor
public Cursor query(String table, String[] columns, String selection,
        String[] selectionArgs, String groupBy, String having,
        String orderBy) {
    return myDataBase.query(table, columns, selection, selectionArgs,
            groupBy, having, orderBy);

}

public Cursor rawQuery(String query) {
    // TODO Auto-generated method stub
    return myDataBase.rawQuery(query, null);
}

}

我在我的 Activity 类中创建了这样的对象:

 DatabaseHelper myDbHelper = new DatabaseHelper(MainActivity.this);

    try {
        myDbHelper.createDataBase();
    } catch (IOException ioe) {
        throw new Error("Unable to create database");
    }

    try {
        myDbHelper.openDataBase();
    } catch (SQLException sqle) {
        throw sqle;
    }
   Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_SHORT).show();
    myDbHelper.close();

我可以通过在游标上运行查询来读取数据 c=myDbhelper.rawquery(query);

什么是插入和删除？如何使用此对象进行插入和删除？

Answer 1

您可以使用以下示例代码在数据库中插入值:

public class DatabaseHandler extends SQLiteOpenHelper {

// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "contactsManager";

// Contacts table name
private static final String TABLE_CONTACTS = "contacts";

// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_PH_NO = "phone_number";

public DatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NO + " TEXT" + ")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

    // Create tables again
    onCreate(db);
}

/**
 * All CRUD(Create, Read, Update, Delete) Operations
 */

// Adding new contact
void addContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.getName()); // Contact Name
    values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone

    // Inserting Row
    db.insert(TABLE_CONTACTS, null, values);
    db.close(); // Closing database connection
}

// Getting single contact
Contact getContact(int id) {
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
            KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
            new String[] { String.valueOf(id) }, null, null, null, null);
    if (cursor != null)
        cursor.moveToFirst();

    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1), cursor.getString(2));
    // return contact
    return contact;
}

// Getting All Contacts
public List<Contact> getAllContacts() {
    List<Contact> contactList = new ArrayList<Contact>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_CONTACTS;

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Contact contact = new Contact();
            contact.setID(Integer.parseInt(cursor.getString(0)));
            contact.setName(cursor.getString(1));
            contact.setPhoneNumber(cursor.getString(2));
            // Adding contact to list
            contactList.add(contact);
        } while (cursor.moveToNext());
    }

    // return contact list
    return contactList;
}

// Updating single contact
public int updateContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.getName());
    values.put(KEY_PH_NO, contact.getPhoneNumber());

    // updating row
    return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
            new String[] { String.valueOf(contact.getID()) });
}

// Deleting single contact
public void deleteContact(Contact contact) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
            new String[] { String.valueOf(contact.getID()) });
    db.close();
}


// Getting contacts Count
public int getContactsCount() {
    String countQuery = "SELECT  * FROM " + TABLE_CONTACTS;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    cursor.close();

    // return count
    return cursor.getCount();
}

}

Contact.java

public class Contact {

    //private variables
    int _id;
    String _name;
    String _phone_number;

    // Empty constructor
    public Contact(){

    }
    // constructor
    public Contact(int id, String name, String _phone_number){
        this._id = id;
        this._name = name;
        this._phone_number = _phone_number;
    }

    // constructor
    public Contact(String name, String _phone_number){
        this._name = name;
        this._phone_number = _phone_number;
    }
    // getting ID
    public int getID(){
        return this._id;
    }

    // setting id
    public void setID(int id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting phone number
    public String getPhoneNumber(){
        return this._phone_number;
    }

    // setting phone number
    public void setPhoneNumber(String phone_number){
        this._phone_number = phone_number;
    }
}