Android studio连接sqlite实现登录注册的代码的详细讲解

首先，建立一个Android Studio项目，然后在项目的build.gradle中添加以下依赖项：

dependencies {
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.squareup.retrofit2:retrofit:2.6.1'
    implementation 'com.squareup.retrofit2:converter-gson:2.6.1'
    implementation 'com.squareup.okhttp3:logging-interceptor:3.12.1'
    implementation 'com.squareup.okhttp3:okhttp:3.12.1'
    implementation 'com.google.code.gson:gson:2.8.5'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.android.support:support-v4:28.0.0'
}

然后，创建一个SQLiteOpenHelper类来创建和管理数据库。在此类中，您可以定义数据库名称，表名称和列名称，以及实现创建表和升级表的方法。

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String TAG = DatabaseHelper.class.getSimpleName();

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "users.db";

    private static final String TABLE_USERS = "users";
    private static final String COLUMN_USER_ID = "_id";
    private static final String COLUMN_USER_NAME = "name";
    private static final String COLUMN_USER_EMAIL = "email";
    private static final String COLUMN_USER_PASSWORD = "password";

    private static final String CREATE_TABLE_USERS = "CREATE TABLE " + TABLE_USERS + "("
            + COLUMN_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + COLUMN_USER_NAME + " TEXT,"
            + COLUMN_USER_EMAIL + " TEXT,"
            + COLUMN_USER_PASSWORD + " TEXT"
            + ")";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE_USERS);
        Log.d(TAG, "Database tables created");
    }

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

    public long addUser(String name, String email, String password) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(COLUMN_USER_NAME, name);
        values.put(COLUMN_USER_EMAIL, email);
        values.put(COLUMN_USER_PASSWORD, password);

        long id = db.insert(TABLE_USERS, null, values);
        db.close();

        Log.d(TAG, "New user inserted into database: " + id);

        return id;
    }

    public boolean checkUser(String email, String password) {
        String[] columns = { COLUMN_USER_ID };
        SQLiteDatabase db = this.getReadableDatabase();

        String selection = COLUMN_USER_EMAIL + " = ?" + " AND " + COLUMN_USER_PASSWORD + " = ?";
        String[] selectionArgs = { email, password };

        Cursor cursor = db.query(TABLE_USERS,
                columns,
                selection,
                selectionArgs,
                null,
                null,
                null);

        int cursorCount = cursor.getCount();
        cursor.close();
        db.close();

        if (cursorCount > 0) {
            return true;
        }

        return false;
    }
}

在这个类中，我们定义了一个名为`users.db`的数据库，以及一个名为`users`的表。表中有4列：`_id`，`name`，`email`和`password`。我们还实现了两个方法：`addUser()`和`checkUser()`。`addUser()`方法用于将新用户添加到数据库中，`checkUser()`方法用于验证用户是否存在于数据库中。

接下来，我们将在MainActivity中实现登录和注册功能。我们在`onCreate()`方法中初始化数据库助手，然后在登录按钮上设置一个点击监听器，该监听器获取输入的电子邮件和密码，然后使用`checkUser()`方法验证用户是否存在于数据库中。

public class MainActivity extends AppCompatActivity {

    private EditText mEmailEditText;
    private EditText mPasswordEditText;
    private Button mLoginButton;
    private Button mRegisterButton;
    private DatabaseHelper mDatabaseHelper;

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

        mDatabaseHelper = new DatabaseHelper(this);

        mEmailEditText = findViewById(R.id.email_edit_text);
        mPasswordEditText = findViewById(R.id.password_edit_text);
        mLoginButton = findViewById(R.id.login_button);
        mRegisterButton = findViewById(R.id.register_button);

        mLoginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String email = mEmailEditText.getText().toString();
                String password = mPasswordEditText.getText().toString();

                if (mDatabaseHelper.checkUser(email, password)) {
                    Toast.makeText(getApplicationContext(), "Login successful", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(getApplicationContext(), "Invalid email or password", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    @Override
    protected void onDestroy() {
        mDatabaseHelper.close();
        super.onDestroy();
    }
}

接下来，我们将在MainActivity中实现注册功能。我们在“注册”按钮上设置一个点击监听器，该监听器获取输入的名称，电子邮件和密码，然后使用`addUser()`方法将新用户添加到数据库中。

mRegisterButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String name = mNameEditText.getText().toString();
        String email = mEmailEditText.getText().toString();
        String password = mPasswordEditText.getText().toString();

        long id = mDatabaseHelper.addUser(name, email, password);

        if (id > 0) {
            Toast.makeText(getApplicationContext(), "Registration successful", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(getApplicationContext(), "Registration failed", Toast.LENGTH_SHORT).show();
        }
    }
});

这就是连接SQLite实现登录和注册的代码的详细讲解。