将游标中的值保存到变量中
Saving value from cursor into a variable
我有一个 android studio 应用程序，它使用 sqlite 保存用户数据，例如用户名、密码等。在用户输入其登录凭据后的登录页面中，用户单击一个按钮调用来自 DatabaseHelper java class 的以下函数检查信息是否正确：
public boolean checkLogin(String username, String password){
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.getCount() > 0){
return true;
}
else {
return false;
}
}
我想保存与该用户匹配的行 ID，以便将来使用它，我正在考虑将该 ID 保存到一个变量中，然后我将使用一个意图将其发送到不同的活动。问题是我不知道如何从查询中保存 ID。
基本上你只需要
cursor.getInt([column position])
或
cursor.getString([column position])
从数据库的列中检索数据。我举了一个例子，希望对你有帮助。有些情况我对编程语言不是很熟悉所以我不能再争论了。
public class User {
private int id;
private String name;
private String password;
private boolean isLogged = false;
public User() {
}
public void setId(int id) {
this.id = id;
}
public int getId() {
return id;
}
public boolean isLogged() {
return isLogged;
}
public void setLogged(boolean x) {
this.isLogged = x;
}
}
检索 Id 的方法要求您可以创建一个字符串或其他内容..
public User checkLogin(String username, String password) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ", new String[] {username, password});
if (cursor.moveToFirst() || cursor.getCount() > 0) {
User user = new User();
user.setId(cursor.getInt(0));//if you created a primary key should be the first column
user.setLogged(true);
cursor.close();// * Closes the Cursor, releasing all of its resources and making it completely invalid.
db.close(); // * Releases a reference to the object, closing the object if the last reference* was released.
return user;
} else {
return null;
}
}
如果 user/password 组合不存在，我建议返回一个 int 而不是布尔值，long 是 id 或 -1。所以：-
public int checkLogin(String username, String password){
int rv = -1;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.moveToFirst()) {
rv = cursor.getInt(cursor.getColumnIndex("id"));
}
cursor.close();
return rv;
}
而不是使用类似的东西：-
if (checkLogin("the_user","the_password")) {
logged in code ....
} else {
not logged in code ....
}
你可以使用类似的东西：-
private int current_userid = -1; // probably declared as a class variable
....
if ((current_userid = db.checkLogin("the_user","the_password")) > 0 ) {
logged in OK code ....
} else {
not logged in code ....
}
I want to save the row ID that matches this user so I can use it in the future and I was thinking of saving the ID into a variable that I will then send to different activities using an intent.
这是一个示例，它执行此操作并将 id 发送到另一个 Activity（下一个 Activity），然后 returns（完成）从 activity 写入登录的用户名和密码。
首先是数据库助手 DBHelper :-
class DBHelper extends SQLiteOpenHelper {
SQLiteDatabase db;
public DBHelper(@Nullable Context context) {
super(context, "mydb", null, 1);
db = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE IF NOT EXISTS user (" +
"id INTEGER PRIMARY KEY, " +
"username TEXT UNIQUE, " +
"password TEXT " +
")");
ContentValues cv = new ContentValues();
cv.put("username","fred");
cv.put("password","password_for_fred");
db.insert("user",null,cv);
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) { }
public int checkLogin(String username, String password){
int rv = -1;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.moveToFirst()) {
rv = cursor.getInt(cursor.getColumnIndex("id"));
}
cursor.close();
return rv;
}
public Cursor getUserById(int userId) {
return db.query("user",null,"id=?",new String[]{String.valueOf(userId)},null,null,null);
}
}
- 请注意，这对 SQLiteDatabase 使用单个 class 变量，因此只需要 1 个 getWriteableDatabase。它还通过在构造函数中包含
db = this.getWriteableDatabase(); 来强制在构造时打开数据库。
- 注意添加的方法
getUserById(ing userId) 方法 returns 根据 userId 的 Cursor。
- 请注意，在创建 table 时会添加一个演示用户。
MainActivity（有点过于复杂，因为它展示了失败的登录尝试（第一次）以及成功的登录尝试（作为处理失败的尝试））：-
public class MainActivity extends AppCompatActivity {
public static final String INTENT_EXTRA_CURRENT_USERID = "current_userid";
DBHelper db;
private int current_userid = -1;
private Intent intent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = new DBHelper(this);
Log.d("LOGIN1","Attempting to Login"); // Will purposefully fail login
if ((current_userid = db.checkLogin("the_user","the_password")) > 0 ) {
Log.d("LOGIN2","Successfully Logged in to user with ID = " + String.valueOf(current_userid));
gotoNextActivity();
} else {
Toast.makeText(this,"Invalid Login, please try again",Toast.LENGTH_SHORT).show();
Log.d("LOGIN1","First attempt to login failed");
// Make 2nd attempt (will work as username and password are correct)
Log.d("LOGIN2","Attemtping to Login (2nd) ");
if((current_userid = db.checkLogin("fred","password_for_fred")) > 0 ) {
Log.d("LOGIN2","Successfully Logged in to user with ID = " + String.valueOf(current_userid));
gotoNextActivity();
}
}
}
private void gotoNextActivity() {
intent = new Intent(this,NextActivity.class);
intent.putExtra(INTENT_EXTRA_CURRENT_USERID,current_userid);
startActivity(intent);
}
}
终于下一个Activity:-
public class NextActivity extends AppCompatActivity {
private int current_userid;
private String current_username, current_password;
private DBHelper db;
Cursor csr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_next);
db = new DBHelper(this);
current_userid = this.getIntent().getIntExtra(MainActivity.INTENT_EXTRA_CURRENT_USERID,-1);
csr = db.getUserById(current_userid);
if (csr.moveToFirst()) {
current_username = csr.getString(csr.getColumnIndex("username"));
current_password = csr.getString(csr.getColumnIndex("password"));
}
if (current_userid > 0) {
Log.d("NEXTACTIVTY","Valid user ID - Username = " + current_username + " password is " + current_password);
} else {
Log.d("NEXTACTIVITY","No Valid userid?");
}
// Finish the Activity and hence return to MainActivity
// Hence it is unlikely that the NextActivity will even be noticed.
finish();
}
@Override
protected void onDestroy() {
super.onDestroy();
if (!csr.isClosed()) {
csr.close();
Log.d("NEXTACTIVITY","Closing Cursor in onDestroy method");
}
}
}
结果
当 运行 日志包括：-
2021-07-17 12:19:37.201 D/LOGIN1: Attempting to Login
2021-07-17 12:19:37.211 D/LOGIN1: First attempt to login failed
2021-07-17 12:19:37.211 D/LOGIN2: Attemtping to Login (2nd)
2021-07-17 12:19:37.212 D/LOGIN2: Successfully Logged in to user with ID = 1
2021-07-17 12:19:37.392 D/NEXTACTIVTY: Valid user ID - Username = fred password is password_for_fred
2021-07-17 12:19:37.745 D/NEXTACTIVITY: Closing Cursor in onDestroy method
我有一个 android studio 应用程序，它使用 sqlite 保存用户数据，例如用户名、密码等。在用户输入其登录凭据后的登录页面中，用户单击一个按钮调用来自 DatabaseHelper java class 的以下函数检查信息是否正确：
public boolean checkLogin(String username, String password){
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.getCount() > 0){
return true;
}
else {
return false;
}
}
我想保存与该用户匹配的行 ID，以便将来使用它，我正在考虑将该 ID 保存到一个变量中，然后我将使用一个意图将其发送到不同的活动。问题是我不知道如何从查询中保存 ID。
基本上你只需要
cursor.getInt([column position])
或
cursor.getString([column position])
从数据库的列中检索数据。我举了一个例子，希望对你有帮助。有些情况我对编程语言不是很熟悉所以我不能再争论了。
public class User {
private int id;
private String name;
private String password;
private boolean isLogged = false;
public User() {
}
public void setId(int id) {
this.id = id;
}
public int getId() {
return id;
}
public boolean isLogged() {
return isLogged;
}
public void setLogged(boolean x) {
this.isLogged = x;
}
}
检索 Id 的方法要求您可以创建一个字符串或其他内容..
public User checkLogin(String username, String password) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ", new String[] {username, password});
if (cursor.moveToFirst() || cursor.getCount() > 0) {
User user = new User();
user.setId(cursor.getInt(0));//if you created a primary key should be the first column
user.setLogged(true);
cursor.close();// * Closes the Cursor, releasing all of its resources and making it completely invalid.
db.close(); // * Releases a reference to the object, closing the object if the last reference* was released.
return user;
} else {
return null;
}
}
如果 user/password 组合不存在，我建议返回一个 int 而不是布尔值，long 是 id 或 -1。所以：-
public int checkLogin(String username, String password){
int rv = -1;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.moveToFirst()) {
rv = cursor.getInt(cursor.getColumnIndex("id"));
}
cursor.close();
return rv;
}
而不是使用类似的东西：-
if (checkLogin("the_user","the_password")) {
logged in code ....
} else {
not logged in code ....
}
你可以使用类似的东西：-
private int current_userid = -1; // probably declared as a class variable
....
if ((current_userid = db.checkLogin("the_user","the_password")) > 0 ) {
logged in OK code ....
} else {
not logged in code ....
}
I want to save the row ID that matches this user so I can use it in the future and I was thinking of saving the ID into a variable that I will then send to different activities using an intent.
这是一个示例，它执行此操作并将 id 发送到另一个 Activity（下一个 Activity），然后 returns（完成）从 activity 写入登录的用户名和密码。
首先是数据库助手 DBHelper :-
class DBHelper extends SQLiteOpenHelper {
SQLiteDatabase db;
public DBHelper(@Nullable Context context) {
super(context, "mydb", null, 1);
db = this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE IF NOT EXISTS user (" +
"id INTEGER PRIMARY KEY, " +
"username TEXT UNIQUE, " +
"password TEXT " +
")");
ContentValues cv = new ContentValues();
cv.put("username","fred");
cv.put("password","password_for_fred");
db.insert("user",null,cv);
}
@Override
public void onUpgrade(SQLiteDatabase db, int i, int i1) { }
public int checkLogin(String username, String password){
int rv = -1;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM user WHERE username=? AND password=? ",
new String[] {username, password});
if (cursor.moveToFirst()) {
rv = cursor.getInt(cursor.getColumnIndex("id"));
}
cursor.close();
return rv;
}
public Cursor getUserById(int userId) {
return db.query("user",null,"id=?",new String[]{String.valueOf(userId)},null,null,null);
}
}
- 请注意，这对 SQLiteDatabase 使用单个 class 变量，因此只需要 1 个 getWriteableDatabase。它还通过在构造函数中包含
db = this.getWriteableDatabase();来强制在构造时打开数据库。 - 注意添加的方法
getUserById(ing userId)方法 returns 根据 userId 的 Cursor。 - 请注意，在创建 table 时会添加一个演示用户。
MainActivity（有点过于复杂，因为它展示了失败的登录尝试（第一次）以及成功的登录尝试（作为处理失败的尝试））：-
public class MainActivity extends AppCompatActivity {
public static final String INTENT_EXTRA_CURRENT_USERID = "current_userid";
DBHelper db;
private int current_userid = -1;
private Intent intent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
db = new DBHelper(this);
Log.d("LOGIN1","Attempting to Login"); // Will purposefully fail login
if ((current_userid = db.checkLogin("the_user","the_password")) > 0 ) {
Log.d("LOGIN2","Successfully Logged in to user with ID = " + String.valueOf(current_userid));
gotoNextActivity();
} else {
Toast.makeText(this,"Invalid Login, please try again",Toast.LENGTH_SHORT).show();
Log.d("LOGIN1","First attempt to login failed");
// Make 2nd attempt (will work as username and password are correct)
Log.d("LOGIN2","Attemtping to Login (2nd) ");
if((current_userid = db.checkLogin("fred","password_for_fred")) > 0 ) {
Log.d("LOGIN2","Successfully Logged in to user with ID = " + String.valueOf(current_userid));
gotoNextActivity();
}
}
}
private void gotoNextActivity() {
intent = new Intent(this,NextActivity.class);
intent.putExtra(INTENT_EXTRA_CURRENT_USERID,current_userid);
startActivity(intent);
}
}
终于下一个Activity:-
public class NextActivity extends AppCompatActivity {
private int current_userid;
private String current_username, current_password;
private DBHelper db;
Cursor csr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_next);
db = new DBHelper(this);
current_userid = this.getIntent().getIntExtra(MainActivity.INTENT_EXTRA_CURRENT_USERID,-1);
csr = db.getUserById(current_userid);
if (csr.moveToFirst()) {
current_username = csr.getString(csr.getColumnIndex("username"));
current_password = csr.getString(csr.getColumnIndex("password"));
}
if (current_userid > 0) {
Log.d("NEXTACTIVTY","Valid user ID - Username = " + current_username + " password is " + current_password);
} else {
Log.d("NEXTACTIVITY","No Valid userid?");
}
// Finish the Activity and hence return to MainActivity
// Hence it is unlikely that the NextActivity will even be noticed.
finish();
}
@Override
protected void onDestroy() {
super.onDestroy();
if (!csr.isClosed()) {
csr.close();
Log.d("NEXTACTIVITY","Closing Cursor in onDestroy method");
}
}
}
结果
当 运行 日志包括：-
2021-07-17 12:19:37.201 D/LOGIN1: Attempting to Login
2021-07-17 12:19:37.211 D/LOGIN1: First attempt to login failed
2021-07-17 12:19:37.211 D/LOGIN2: Attemtping to Login (2nd)
2021-07-17 12:19:37.212 D/LOGIN2: Successfully Logged in to user with ID = 1
2021-07-17 12:19:37.392 D/NEXTACTIVTY: Valid user ID - Username = fred password is password_for_fred
2021-07-17 12:19:37.745 D/NEXTACTIVITY: Closing Cursor in onDestroy method