Question

我基本上使用this tutorial来创建一个SQLite数据库，这很好。我现在有一个名为camera的新类，我想获取数据库中的所有（或单个）电话号码，但我不知道如何在新类中调用数据库。

我试着看看其他的例子，但是他们在这里使用了DatabaseHelper而不是Handler，而且代码是以不同的方式构造的，这让我很困惑。

我的问题是：如何在新的相机课程中调用我的数据库并获取我需要的所有信息（电话号码）？我不知道这是否重要，但我想在OnClickView事件中打开数据库

DatabaseHandler.java

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();
    }

我要在OnClickView

中为数据库调用的相机类

  public camera extends Activity {
        protected Dialog mSplashDialog;
        private Button foto;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
                populateBtn();
    }

private void populateBtn() {
        foto1 = (Button) this.findViewById(R.id.button2);
        foto1.setOnClickListener(new View.OnClickListener() {
            @SuppressLint("SimpleDateFormat")
            @Override
            public void onClick(View v) 
// here is where i want to call for the database (to get a single, or all the phone numbers)
}

联系班级

Contact.java
package com.androidhive.androidsqlite; 

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;
    }
}

Answer 1

来自您的相机类：

DatabaseHandler myDatabase = new DatabaseHandler(this);
List<Contact> allContacts = myDatabase.getAllContacts();
// do something with your contacts...

希望这会有所帮助。只是指出DatabaseHandler在构造函数中需要一个Context，因此，只要您的类摄像头从Activity扩展，它就可以工作。

Answer 2

只需创建DatabaseHandler类的实例并使用其方法。

获取所有联系人：

DatabaseHandler db = new DatabaseHandler(this);
List<Contact> contacts = db.getAllContacts();
for (Contact contact : contacts) {
    // use your contact methods...
}

对于一位联系人：

DatabaseHandler db = new DatabaseHandler(this);
Contact contact = db.getContact(your_id);
// use your contact methods...

仅当您在Activity类中时才使用this。否则你将需要一个有效的上下文。

更新

OnClickListener是一个内部类。您需要将其外部类用作有效上下文。使用：

private void populateBtn() {
    foto1 = (Button) this.findViewById(R.id.button2);
    foto1.setOnClickListener(new View.OnClickListener() {
        @SuppressLint("SimpleDateFormat")
        @Override
        public void onClick(View v) 
            DatabaseHandler db = new DatabaseHandler(camera.this);
            List<Contact> contacts = db.getAllContacts();
            for (Contact contact : contacts) {
                // use your contact methods...
             }
        }
     }
 }

Answer 3

// Reading all contacts
    Log.d("Reading: ", "Reading all contacts..");
    List<CompanysContact> contacts = db.getAllContacts();       

    for (CompanysContact cn : contacts) {
        String log = "Id: "+cn.getID()+" ,Name: " + cn.getName()
                     + " ,Phone: " + cn.getPhoneNumber() ;
            // Writing Contacts to log
    Log.d("Name: ", log);

    }

将数据库信息提供给Android中的另一个类

3 个答案: