Question

如何为sqlite创建一个简单的SignUp（Email，UserName，Password）。然后使用他们的UserName＆amp; SignIn / LogIn。密码？

我尝试了这段代码，但在插入时遇到错误。此代码在SignUp上编写

String user=username.getText().toString();
String pass=password.getText().toString();
String mail=email.getText().toString();

if ((user.matches(""))||(pass.matches(""))||(mail.matches(""))) {
   Log.d("SignUp", "Vacant Field");
   return;
}
else {
    DatabaseAdapter dbadapter=new DatabaseAdapter(null);
    dbadapter.insertdata(user, pass, mail);

    Log.d("SignUp", "Data's stored in SQLite");
}

在 DatabaseAdapter 类中，我使用了此代码

public class DatabaseAdapter {

static final String DATABASE_NAME = "login.db";
static final int DATABASE_VERSION = 1;
public static final int NAME_COLUMN = 1;

// SQL to Create a new Database
static final String DATABASE_CREATE= "create table "+"LOGIN"+
        "( " +"ID"+" integer primary key autoincrement,"+ "USERNAME  text,PASSWORD text, EMAIL text); ";

// Variable to hold the database instance
public SQLiteDatabase db;

// Context of the application using the database.
private final Context context;

// Database open/upgrade helper
private DataBaseHelper dbHelper;

public DatabaseAdapter(Context _context)
{
    context = _context;
    dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
}

public DatabaseAdapter open() throws SQLException
{
    db = dbHelper.getWritableDatabase();
    return this;
}

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

public  SQLiteDatabase getDatabaseInstance()
{
    return db;
}

// to store data`s in SQLite db
public void insertdata(String username, String password, String email)
{
    ContentValues values=new ContentValues();

    // Assign values for each row.
    values.put("USERNAME", username);
    values.put("PASSWORD", password);
    values.put("EMAIL", email);
    Log.d("DatabaseAdapter", "Data's are assin to insert");

    // Insert the row into your table
    db.insert("LOGIN", null, values);
    Log.d("DatabaseAdapter", "Data's stored successfully");
    db.close();
}

public String getSingleEntry(String userName)
{
    Cursor cursor=db.query("LOGIN", null, " USERNAME=?", new String[]{userName}, null, null, null);
    if(cursor.getCount()<1) // UserName Not Exist
    {
        cursor.close();
        return "NOT EXIST";
    }
    cursor.moveToFirst();
    String password= cursor.getString(cursor.getColumnIndex("PASSWORD"));
    cursor.close();
    return password;
   }
}

按下SignUp按钮时出现错误

 FATAL ERROR, Null pointer Exception Error

Answer 1

DatabaseAdapter dbadapter=new DatabaseAdapter(null);这就是你犯错的地方。您应该传递当前活动而不是null。

正确的调用语法应如下所示，

 DatabaseAdapter dbadapter=new DatabaseAdapter(this);

Answer 2

signup.java（活动）

package...name;

    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.view.View;
    import android.widget.EditText;
    import android.widget.TextView;
    import android.widget.Toast;

    public class signup extends AppCompatActivity {
    DatabaseHelper helper = new DatabaseHelper(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_signup);

        //to link to the second activity
        TextView loginScreen = (TextView) findViewById(R.id.link_to_login);
        // Listening to Login Screen link
        loginScreen.setOnClickListener(new View.OnClickListener() {

            public void onClick(View arg0) {
                // Closing registration screen
                // Switching to Login Screen/closing register screen
                finish();
            }
        });
    }
    public void onSignUpClick(View v){
        if(v.getId() == R.id.btn_Register)
        {
            EditText name = (EditText)findViewById(R.id.TFname);
            EditText email = (EditText)findViewById(R.id.TFemail);
            EditText pass1 = (EditText)findViewById(R.id.TFpass1);
            EditText pass2 = (EditText)findViewById(R.id.TFpass2);

            String namestr = name.getText().toString();
            String emailstr = name.getText().toString();
            String pass1str = name.getText().toString();
            String pass2str = name.getText().toString();

            if(!pass1str.equals(pass2str))
            {
                //popup msg:
                Toast tpass = Toast.makeText(signup.this, "passwords don't match", Toast.LENGTH_LONG);
                tpass.show();
            }
            else
            {
                //insert the details in DB:
                Contact c = new Contact();
                c.setName(namestr);
                c.setEmail(emailstr);
                c.setPass(pass1str);

                helper.insertContact(c);
            }

        }
    }

}

DatabaseHelper.java（Class）

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


public class DatabaseHelper extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "contacts.db";
    private static final String TABLE_NAME = "contacts";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_NAME = "name";
    private static final String COLUMN_EMAIL = "email";
    private static final String COLUMN_UNAME = "uname";
    private static final String COLUMN_PASS = "pass";
    SQLiteDatabase db;
    private static final String TABLE_CREATE="create table contacts (id integer primary key not null ," +
            "name text not null, email text not null, uname text not null, pass text not null);";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(TABLE_CREATE);
        this.db = db;
    }

    public void insertContact(Contact c)
    {
        db = this.getWritableDatabase();
        ContentValues values = new ContentValues();

        //create a string query
        String query = "select  * from contacts ";
        Cursor cursor = db.rawQuery(query, null);
        int count = cursor.getCount();

        values.put(COLUMN_ID, count);
        values.put(COLUMN_NAME, c.getName());
        values.put(COLUMN_EMAIL, c.getEmail());
        values.put(COLUMN_PASS, c.getPass());

        //this will insert the content in the database
        db.insert(TABLE_NAME, null, values);
        db.close();
    }

    public String searchPass(String name){

        db = this.getReadableDatabase();
        String query = "select name, pass from" +TABLE_NAME;
        Cursor cursor = db.rawQuery(query, null);
        String a, b;
        b="not found";
        if(cursor.moveToFirst()){
            do{
                a=cursor.getString(0);

                if(a.equals(name)){
                    b=cursor.getString(1);
                    break;
                }
            }
            while (cursor.moveToNext());
        }
        return b;
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String query = "DROP TABLE IF EXISTS"+TABLE_NAME;
        db.execSQL(query);
        this.onCreate(db);
    }
}

Contact.java（class）

public class Contact {
    String name, email, uname, pass;


    public void setName(String name)
    {
        this.name  = name;
    }
    public String getName()
    {
        return this.name;
    }
    public void setEmail(String email)
    {
        this.email  = email;
    }
    public String getEmail()
    {
        return this.email;
    }
    public void setUname(String uname)
    {
        this.uname  = uname;
    }
    public String getUname()
    {
        return this.uname;
    }
    public void setPass(String pass)
    {
        this.pass  = pass;
    }
    public String getPass()
    {
        return this.pass;
    }

}

Login.java（活动）

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class Login extends Activity {

    DatabaseHelper helper = new DatabaseHelper(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        TextView registerScreen = (TextView) findViewById(R.id.link_to_signup);

        // Listening to register new account link
        registerScreen.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {
                // Switching to Register screen
                Intent i = new Intent(getApplicationContext(), signup.class);
                startActivity(i);
            }
        });
    }
    public void onSigninClick(View v){
        if(v.getId() == R.id.btnLogin)
        {
            EditText a = (EditText)findViewById(R.id.TFname);
            String str = a.getText().toString();
            EditText b = (EditText)findViewById(R.id.TFpassword);
            String pass = a.getText().toString();

            String password = helper.searchPass(str);
            if(pass.equals(password))
            {
                Intent i = new Intent(Login.this, signup.class);
                i.putExtra("name" , str);
                startActivity(i);
            }
            else{//popup msg:
                Toast temp = Toast.makeText(Login.this, "username & passwords don't match", Toast.LENGTH_LONG);
                temp.show();}
        }

    }
}

Display.java（活动）

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class Display extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_display);
        String name = getIntent().getStringExtra("name");
        TextView tv = (TextView)findViewById(R.id.TFname);
        tv.setText(name);
    }

}

Answer 3

主要活动

Button login_button;
    EditText email_edit, password_edit;
    TextView goToRegister;
    DatabaseHelper userDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login);

        email_edit = (EditText) findViewById(R.id.edit_email_login);
        password_edit = (EditText) findViewById(R.id.edit_password_login);
        userDatabase = new DatabaseHelper(this);

        //Go to Register Activity
        goToRegister = (TextView) findViewById(R.id.go_to_register);
        goToRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent goToRegister = new Intent(MainActivity.this, RegisterActivity.class);
                startActivity(goToRegister);


            }
        });

        login_button = (Button) findViewById(R.id.button_register);
        login_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (validate()) {

                    //Get values from EditText fields
                    String email = email_edit.getText().toString();
                    String password = password_edit.getText().toString();

                    //Authenticate User
                    User currentUser = userDatabase.Authenticate(new User(null, null, email, password));

                    //Check Authentication is successful or not
                    if (currentUser != null) {
                        Intent goToDash = new Intent(MainActivity.this, DashboardActivity.class);
                        goToDash.putExtra("Email", currentUser.email);
                        goToDash.putExtra("Name", currentUser.name);
                        startActivity(goToDash);
                        Toast.makeText(MainActivity.this, " Login Successful!", Toast.LENGTH_SHORT).show();

                    } else {
                        Toast.makeText(MainActivity.this, " Failed to Logged in!", Toast.LENGTH_LONG).show();
                    }
                }
            }
        });
    }

    private boolean validate() {
        boolean valid = false;

        //Get values from EditText fields
        String email = email_edit.getText().toString();
        String pass = password_edit.getText().toString();

        //Handling validation
        if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            valid = false;
            email_edit.setError("Please enter valid Email");
        } else {
            valid = true;
            email_edit.setError(null);

        }

        //Handling Password
        if (pass.isEmpty()) {
            valid = false;
            password_edit.setError("Please enter Valid Password");
        }
        return valid;
    }
}

注册活动

 Button register_butoon;
    TextView goToLogin;
    EditText edit_email, edit_password, edit_confirm_pass, edit_full_name;
    DatabaseHelper userDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);

        userDatabase = new DatabaseHelper(this);

        edit_full_name = (EditText) findViewById(R.id.edit_full_name);
        edit_email = (EditText) findViewById(R.id.edit_email_register);
        edit_password = (EditText) findViewById(R.id.edit_password_register);
        edit_confirm_pass = (EditText) findViewById(R.id.edit_confirm_pass);

        register_butoon = (Button) findViewById(R.id.button_register);

        goToLogin = (TextView) findViewById(R.id.register_text_view);

        goToLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent goToLogin = new Intent(RegisterActivity.this, MainActivity.class);
                startActivity(goToLogin);

            }
        });

        register_butoon.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if (validate()) {

                    //Get Input From edit text
                    String userName = edit_full_name.getText().toString();
                    String userEmail = edit_email.getText().toString();
                    String userPass = edit_password.getText().toString();
                    String userConfirmationPass = edit_confirm_pass.getText().toString();

                    if (userConfirmationPass.equals(userPass) && !userDatabase.isEmailExists(userEmail)) {

                        //Insert data in Database from EditText field
                        userDatabase.addUser(new User(null, userName, userEmail, userPass));
                        Toast.makeText(RegisterActivity.this, "User created successfully! Please Login ", Toast.LENGTH_LONG).show();
                        new Handler().postDelayed(new Runnable() {
                            @Override
                            public void run() {
                                finish();
                            }
                        }, Toast.LENGTH_LONG);

                    } else if (!userConfirmationPass.equals(userPass)) {
                        Toast.makeText(RegisterActivity.this, "Password is not Matched ", Toast.LENGTH_LONG).show();

                    } else {
                        Toast.makeText(RegisterActivity.this, "User already exists , Check your email ", Toast.LENGTH_LONG).show();

                    }

                }

            }
        });
    }


    //This method is used to validate input given by user
    public boolean validate() {
        boolean valid = false;

        //Get values from EditText fields
        String UserName = edit_full_name.getText().toString();
        String Email = edit_email.getText().toString();
        String Password = edit_password.getText().toString();

        //Handling validation for UserName field
        if (UserName.isEmpty()) {
            valid = false;
            edit_full_name.setError("Please enter valid username!");
        } else {
            if (UserName.length() > 5) {
                valid = true;
                edit_full_name.setError(null);
            } else {
                valid = false;
                edit_full_name.setError("Username is to short!");
            }
        }

        //Handling validation for Email field
        if (!Patterns.EMAIL_ADDRESS.matcher(Email).matches()) {
            valid = false;
            edit_email.setError("Please enter valid email!");
        } else {
            valid = true;
            edit_email.setError(null);
        }

        //Handling validation for Password field
        if (Password.isEmpty()) {
            valid = false;
            edit_password.setError("Please enter valid password!");
        } else {
            if (Password.length() > 2) {
                valid = true;
                edit_password.setError(null);
            } else {
                valid = false;
                edit_password.setError("Password is to short!");
            }
        }
        return valid;
    }
}

个人资料活动或仪表板活动

  TextView email_display, user_name;
    Button logOut;
    DatabaseHelper userDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.dashboard);

        userDatabase = new DatabaseHelper(this);

        logOut = (Button) findViewById(R.id.logout);
        logOut.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //Finish current Activity
                finish();
                Toast.makeText(DashboardActivity.this, "LogOut Successful", Toast.LENGTH_SHORT).show();
            }
        });

        email_display = (TextView) findViewById(R.id.display_email);
        user_name = (TextView) findViewById(R.id.user_name);

        Intent i = this.getIntent();
        String email = i.getStringExtra("Email");
        String name = i.getStringExtra("Name");

        user_name.setText(name);
        email_display.setText(email);

    }
}

DatabaseHelper类

//Table Name
    public static final String TABLE_NAME = "user";
    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "UserManager.db";

    // User Table Columns names
    public static final String COLUMN_USER_ID = "user_id";
    public static final String COLUMN_USER_NAME = "user_name";
    public static final String COLUMN_USER_EMAIL = "user_email";
    public static final String COLUMN_USER_PASSWORD = "user_password";

    // create table sql query
    private String CREATE_USER_TABLE = "CREATE TABLE " + TABLE_NAME + "("
            + COLUMN_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + COLUMN_USER_NAME + " TEXT,"
            + COLUMN_USER_EMAIL + " TEXT,"
            + COLUMN_USER_PASSWORD + " TEXT" + ")";

    // drop table sql query
    private String DROP_USER_TABLE = "DROP TABLE IF EXISTS " + TABLE_NAME;

    /**
     * Constructor
     *
     * @param context
     */
    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

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


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

        //Drop User Table if exist
        db.execSQL(DROP_USER_TABLE);

        // Create tables again
        onCreate(db);

    }

    //Add user in Database
    public void addUser(User user) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();

        values.put(COLUMN_USER_NAME, user.name);
        values.put(COLUMN_USER_EMAIL, user.email);
        values.put(COLUMN_USER_PASSWORD, user.password);

        //Inserting row
        db.insert(TABLE_NAME, null, values);

        //Close the database
        db.close();
    }

    public User Authenticate(User user) {

        // array of columns to fetch
        String[] columns = {
                COLUMN_USER_ID,
                COLUMN_USER_NAME,
                COLUMN_USER_EMAIL,
                COLUMN_USER_PASSWORD
        };
        SQLiteDatabase db = this.getReadableDatabase();

        Cursor cursor = db.query(TABLE_NAME, //Table to query
                columns,                    //columns to return
                null,                  //columns for the WHERE clause
                null,              //The values for the WHERE clause
                null,                       //group the rows
                null,                       //filter by row groups
                null);                      //The sort order
        if (cursor != null && cursor.moveToFirst() && cursor.getCount() > 0) {
            do {

                User user1 = new User(cursor.getString(cursor.getColumnIndex(this.COLUMN_USER_ID)),
                        cursor.getString(cursor.getColumnIndex(this.COLUMN_USER_NAME)),
                        cursor.getString(cursor.getColumnIndex(this.COLUMN_USER_EMAIL)),
                        cursor.getString(cursor.getColumnIndex(this.COLUMN_USER_PASSWORD)));

                if (user.password.equalsIgnoreCase(user1.password) && user.email.equals(user1.email)) {
                    return user1;

                }
            } while (cursor.moveToNext());

        }
        cursor.close();
        return null;
    }

    public boolean isEmailExists(String email) {
        SQLiteDatabase db = this.getReadableDatabase();

        // array of columns to fetch
        String[] columns = {COLUMN_USER_EMAIL};

        //Selection
        String selection = COLUMN_USER_EMAIL + " = ? ";

        //Selection Args
        String[] selection_Args = {email};

        //Query
        Cursor cursor = db.query(TABLE_NAME,
                columns,
                selection,
                selection_Args,
                null,
                null,
                null
        );

        if (cursor != null && cursor.moveToFirst() && cursor.getCount() > 0) {
            return true;
        }
        return false;
    }
}

用户类别

public class User {

    //Variable
    public String id;
    public String name;
    public String email;
    public String password;

    //Constructor with two parameters
    public User(String email, String password) {
        this.email = email;
        this.password = password;
    }

    //Parameter Constructor containing all three parameter
    public User(String id, String name, String email, String password) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.password = password;

    }
}

完成SignIn＆amp;使用sqlite数据库在Android中注册？

3 个答案: