如何在Android

Question

我正在尝试在android中创建一个登录应用程序。如何从其他活动访问数据库？一旦用户在主活动上输入他的用户名和密码，他就会从数据库中检查他的详细信息。另外，如何让他在同一个数据库中使用单独的活动进行注册？

Answer 1

按照我的步骤。

首先创建xml文件，如下所示：

<?xml version="1.0" encoding="UTF-8"?>

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:padding="10dip">


    <TextView
        android:id="@+id/lblUsername"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp" android:text="Username:"
        android:textStyle="bold"
        android:layout_marginBottom="8dip"

        />

    <EditText
        android:id="@+id/txtUsername"
        android:layout_below="@id/lblUsername"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="12sp"
        android:layout_marginBottom="8dip"
        />

    <TextView
        android:id="@+id/lblPassword"
        android:layout_below="@id/txtUsername"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp" android:text="Password:"
        android:textStyle="bold"
        android:layout_marginBottom="8dip"

        />

    <EditText
        android:id="@+id/txtPassword"
        android:layout_below="@id/lblPassword"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textSize="12sp"
        android:layout_marginBottom="8dip"
        android:password="true"
        />



    <Button
        android:id="@+id/btnLogin"
        android:layout_below="@id/txtPassword"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Login"
        />

</RelativeLayout>

创建一个数据库类：

package com.example.danish;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBUserAdapter 
{ 
    public static final String KEY_ROWID = "_id";
    public static final String KEY_USERNAME= "username";
    public static final String KEY_PASSWORD = "password";    
    private static final String TAG = "DBAdapter";

    private static final String DATABASE_NAME = "usersdb";
    private static final String DATABASE_TABLE = "users";
    private static final int DATABASE_VERSION = 1;

    private static final String DATABASE_CREATE =
        "create table users (_id integer primary key autoincrement, "
        + "username text not null, " 
        + "password text not null);";

    private Context context = null;  
    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public DBUserAdapter(Context ctx) 
    {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper 
    {
        DatabaseHelper(Context context) 
        {
            super(context, "/sdcard/folderName/"+DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) 
        {
            db.execSQL(DATABASE_CREATE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
        {
            Log.w(TAG, "Upgrading database from version " + oldVersion 
                    + " to "
                    + newVersion + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS users");
            onCreate(db);
        }
    }    


    public void open() throws SQLException 
    {
        db = DBHelper.getWritableDatabase();
    }


    public void close() 
    {
        DBHelper.close();
    }    

    public long AddUser(String username, String password)
    {
         ContentValues initialValues = new ContentValues();
         initialValues.put(KEY_USERNAME, username);
         initialValues.put(KEY_PASSWORD, password);       
         return db.insert(DATABASE_TABLE, null, initialValues);

    }

    public boolean Login(String username, String password) throws SQLException 
    {
        Cursor mCursor = db.rawQuery("SELECT * FROM " + DATABASE_TABLE + " WHERE username=? AND password=?", new String[]{username,password});
        if (mCursor != null) {           
            if(mCursor.getCount() > 0)
            {
                return true;
            }
        }
     return false;
    }

}

最后创建您的登录活动：

package com.example.danish;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class LoginActivity extends Activity 
{
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);
        final EditText txtUserName = (EditText)findViewById(R.id.txtUsername);
        final EditText txtPassword = (EditText)findViewById(R.id.txtPassword);
        Button btnLogin = (Button)findViewById(R.id.btnLogin);
        btnLogin.setOnClickListener(new OnClickListener(){

            @Override
            public void onClick(View v) {
                String username = txtUserName.getText().toString();
                String password = txtPassword.getText().toString();
                try{
                    if(username.length() > 0 && password.length() >0)
                    {
                        DBUserAdapter dbUser = new DBUserAdapter(LoginActivity.this);
                        dbUser.open();

                        if(dbUser.Login(username, password))
                        {
                            Toast.makeText(LoginActivity.this,"Successfully Logged In", Toast.LENGTH_LONG).show();
                        }else{
                            Toast.makeText(LoginActivity.this,"Invalid Username/Password", Toast.LENGTH_LONG).show();
                        }
                        dbUser.close();
                    }

                }catch(Exception e)
                {
                    Toast.makeText(LoginActivity.this,e.getMessage(), Toast.LENGTH_LONG).show();
                }
            }

        });
    }
}

注意：在寄存器的情况下，我已经在Database类中编写了该方法，但您必须调用自身才能在数据库中插入值。我刚刚调用了login方法，它会检查数据库中是否存在值。

Answer 2

创建单独的数据库类，如下所示

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;
    }
} 

来自不同活动的电话

DatabaseHandler databaseHandler = new DatabaseHandler(this);
databaseHandler .getContact(15);

Answer 3

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;
    }
}