Question

我正在尝试制作一个使用Firebase来存储学生的电子邮件和密码的应用程序。但是对于存储任何特定用户的登录会话（例如，如果该用户尚未显式注销并终止该应用程序，则不会要求他/她再次登录并将其直接带到HomeScreen）使用SQLite数据库。但是我的应用程序在尝试访问MyDatabasehelper类中的方法的主屏幕本身上崩溃了。

1）Mydatabasehelper.class 公共类MyDatabaseHelper扩展了SQLiteOpenHelper {

private static final int DATABASE_VERSION = 1; //databse version always starts with 1 (NOT 0)
public static final String TABLE_NAME = "Login";
private static final String DATABASE_NAME = "login.db";
private static final String COLUMN_0_Id = "Id";
private static final String COLUMN_1_IsLogin = "LoginData";

//override these 2 methods (otherwise error on the inheritance)

public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {

    //2 ways -> 1) create string variable and store the query in it 2)
    String CREATE_LOGIN_TABLE = "CREATE TABLE " + TABLE_NAME + "(Id INT PRIMARY KEY, IsLogin INT)";
    sqLiteDatabase.execSQL(CREATE_LOGIN_TABLE); //executing the query using the SQLiteDatabase object 'db' that we get as a parameter
    Insert();

}

//if we are changing the schema of our database, the database gets 'upgraded'
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
    onCreate(sqLiteDatabase);
}

private void Insert() {
    //class which allows us to specify values in the 'key - value' pair way
    ContentValues values = new ContentValues();

    values.put(COLUMN_0_Id, 1);
    values.put(COLUMN_1_IsLogin,0);

    SQLiteDatabase db = this.getWritableDatabase();
    long r = db.insert(TABLE_NAME, null, values);
    Log.d("Return Value : ", String.valueOf(r));
    db.close();
}

public LoginData Search(int StuRN) {
    SQLiteDatabase db = this.getWritableDatabase();

    String query = "SELECT * FROM " + TABLE_NAME + " WHERE Id=" + StuRN;
    Cursor result = db.rawQuery(query, null);

    LoginData logindata=new LoginData();

    if (result.moveToFirst()) {
        logindata.setId(StuRN);
        logindata.setIsLogin(result.getInt(1));

        result.close();
    }
    else {
        logindata = null;
    }
    return logindata;

}

public void updateData(int IsLogin) {
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put(COLUMN_1_IsLogin, IsLogin);
    db.update(TABLE_NAME, contentValues, COLUMN_0_Id + " = " + "1", null);

}
    }

2）MainActivity.class 公共类MainActivity扩展了AppCompatActivity {

private static int SPLASH = 2000;
//private Cursor cursor;
MyDatabaseHelper dbHandler;
LoginData logindata;

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

    dbHandler = new MyDatabaseHelper(MainActivity.this, null, null, 1);
    logindata = new LoginData();

    LoginData l=dbHandler.Search(1);

    final int display=logindata.getIsLogin();
    new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(MainActivity.this,display,Toast.LENGTH_SHORT).show();
                Intent intent = new Intent(MainActivity.this, Login.class);
                startActivity(intent);
                finish();

            }
        },SPLASH);



}
    }

3）错误 AndroidRuntime：致命异常：main 流程：com.example.android.cummins，PID：22698 java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.android.cummins / com.example.android.cummins.MainActivity}：java.lang.IllegalStateException：getDatabase递归调用在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2560）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2626）在android.app.ActivityThread.-wrap11（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1475）在android.os.Handler.dispatchMessage（Handler.java:111）在android.os.Looper.loop（Looper.java:207）在android.app.ActivityThread.main（ActivityThread.java:5740）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:905）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:766）引起原因：java.lang.IllegalStateException：getDatabase递归调用在android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked（SQLiteOpenHelper.java:203）在android.database.sqlite.SQLiteOpenHelper.getWritableDatabase（SQLiteOpenHelper.java:163）在com.example.android.cummins.MyDatabaseHelper.Insert（MyDatabaseHelper.java:49）在com.example.android.cummins.MyDatabaseHelper.onCreate（MyDatabaseHelper.java:30）在android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked（SQLiteOpenHelper.java:251）在android.database.sqlite.SQLiteOpenHelper.getReadableDatabase（SQLiteOpenHelper.java:187）在com.example.android.cummins.MyDatabaseHelper.Search（MyDatabaseHelper.java:56）在com.example.android.cummins.MainActivity.onCreate（MainActivity.java:26）在android.app.Activity.performCreate（Activity.java:6543）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1113）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2513）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2626）在android.app.ActivityThread.-wrap11（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1475）在android.os.Handler.dispatchMessage（Handler.java:111）在android.os.Looper.loop（Looper.java:207）在android.app.ActivityThread.main（ActivityThread.java:5740）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:905）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:766） I / Process：正在发送信号。 PID：22698 SIG：9 应用已终止。

连接到SQLite并尝试访问其方法时，应用程序崩溃

0 个答案: