Question

我需要帮助。我已经研究了一周来解决我的问题，而且找不到解决方案。

我已经放了一些代码，逻辑上它会起作用。

我的问题是我想从数据库（SQLite）获取信息并将其保存到变量中。

当我按下按钮（getLoginInfo）时，它将使应用程序崩溃。这是代码。

DBHandler.java

package project.asyraf.sar;

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

public class DBHandler extends SQLiteOpenHelper {

public static final String DATABASE_NAME = "kypsarv2.db";
public static final int DATABASE_VERSION = 1;

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

@Override
public void onCreate(SQLiteDatabase db) {

    String createTableLoginInfo = "CREATE TABLE loginInfo (id INTEGER PRIMARY KEY AUTOINCREMENT, username TEXT, password TEXT, accesslevel TEXT, owner TEXT);";
    db.execSQL(createTableLoginInfo);
    String createTableAdmin = "CREATE TABLE admin (id INTEGER PRIMARY KEY AUTOINCREMENT, adminName TEXT, adminIC);";
    db.execSQL(createTableAdmin);
    String createTableLect = "CREATE TABLE lecturer (id INTEGER PRIMARY KEY AUTOINCREMENT, lecturerName TEXT, lecturerIC);";
    db.execSQL(createTableLect);
    String createTableStud = "CREATE TABLE student (id INTEGER PRIMARY KEY AUTOINCREMENT, studentName TEXT, studentIC);";
    db.execSQL(createTableStud);
    String createTableReminder = "CREATE TABLE reminder (id INTEGER PRIMARY KEY AUTOINCREMENT, subject TEXT, activity TEXT, startDate DATE, endDate DATE, description TEXT, owner TEXT);";
    db.execSQL(createTableReminder);
}

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

    db.execSQL("DROP TABLE IF EXISTS loginInfo");
    db.execSQL("DROP TABLE IF EXISTS admin");
    db.execSQL("DROP TABLE IF EXISTS lecturer");
    db.execSQL("DROP TABLE IF EXISTS student");
    db.execSQL("DROP TABLE IF EXISTS reminder");

    onCreate(db);
}

protected String owner, accessLevel;

public void getLoginInfo (String username, String password)
{
    Cursor cursor = this.getReadableDatabase().rawQuery("SELECT * FROM loginInfo WHERE username = ? AND password = ?", new String[] {username, password});
    cursor.moveToFirst();

    accessLevel = cursor.getString(3);
    owner = cursor.getString(4);

    cursor.close();
}

LoginMenu.java

 package project.asyraf.sar;

import android.content.Intent;
import android.database.Cursor;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class LoginMenu extends AppCompatActivity {

DBHandler useDB = new DBHandler(this);

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

public void closeApps (View view){
    finish();
}

public void loginTrial (View view) {

    final EditText getUsername = (EditText) findViewById(R.id.username);
    final EditText getPassword = (EditText) findViewById(R.id.password);

    String textUsername, textPassword = "";

    textUsername = getUsername.getText().toString();
    textPassword = getPassword.getText().toString();

    Intent loginSuccessLecturer = new Intent (this, LecturerDashboard.class);
    Intent loginSuccessStudent = new Intent (this, StudentDashboard.class);
    Intent loginSuccessAdmin = new Intent (this, AdminDashboard.class);

    //Cursor getLogin = useDB.getLoginData(textUsername, textPassword);

    useDB.getLoginInfo(textUsername, textPassword);

    String owner = "";
    String accessLevel = "";
    owner = useDB.owner;
    accessLevel = useDB.accessLevel;

    StringBuffer buffer = new StringBuffer();

    if (textUsername.equals("") || textPassword.equals(""))
    {
        Toast.makeText(getApplicationContext(), "Enter Username or Password", Toast.LENGTH_SHORT).show();
    }
    else if (textUsername.equals("admin") && textPassword.equals("admin"))
    {
        startActivity(loginSuccessAdmin);
    }
    else
    {
        if (owner.equals(""))
        {
            Toast.makeText(getApplicationContext(), "User do not exist", Toast.LENGTH_SHORT).show();
        }
        else
        {
            if (accessLevel.equals("student"))
            {
                startActivity(loginSuccessStudent);
            }
            else if (accessLevel.equals("lecturer"))
            {
                startActivity(loginSuccessLecturer);
            }
        }
    }

    /*
    if (owner.equals(""))
    {
        Toast.makeText(getApplicationContext(), "No Data", Toast.LENGTH_SHORT).show();
    }
    else
    {
        //showMessage("Data",buffer.toString());
        if (!owner.equals("") && accessLevel.equals("student"))
        {
            startActivity(loginSuccessAdmin);
        }
        else
            Toast.makeText(getApplicationContext(), "Login Error, Please Login Again", Toast.LENGTH_SHORT).show();

        if (textUsername.equals(usernameInfo) && textPassword.equals(passwordInfo))
        {
            if (accessInfo.equals("admin"))
            {
                //startActivity(loginSuccessAdmin);
            }
            else if (accessInfo.equals("student"))
            {
                Toast.makeText(getApplicationContext(), "Login to Student", Toast.LENGTH_SHORT).show();
                //startActivity(loginSuccessStudent);
            }
            else if (accessInfo.equals("lecturer"))
            {
                //startActivity(loginSuccessLecturer);
            }
            else
                Toast.makeText(getApplicationContext(), "Access Error, Please Login Again", Toast.LENGTH_SHORT).show();
        }
        else
        {
            Toast.makeText(getApplicationContext(), "Login Error, Please Login Again", Toast.LENGTH_SHORT).show();
        }
    }*/
}
}

错误日志

android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0                           
                                                   at project.asyraf.sar.DBHandler.getLoginInfo(DBHandler.java:144)
                                                   at project.asyraf.sar.LoginMenu.loginTrial(LoginMenu.java:44)

DBHandler.java:144（accessLevel = cursor.getString（3）;）

LoginMenu.java:44（useDB.getLoginInfo（textUsername，textPassword）;）

Answer 1

假设其他一切正常，您的数据库有一个空的Context，因此您需要将其初始化移动到onCreate，其中Context不为null。

DBHandler useDB;

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

    useDB = new DBHandler(this);
}

虽然，问题似乎是Cursor是空的（没有列）

请求索引0，大小为0

在这种情况下，您需要手动卸载应用程序并重新运行以重新创建表格。

要编写不易出错的查询，可以试试这个。

if (cursor != null && cursor.moveToFirst()) {
    accessLevel = cursor.getString(cursor.getColumnIndex("accessLevel"));
    owner = cursor.getString(cursor.getColumnIndex("owner"));
}

如果在尝试访问这些变量时出现错误或无效，则检查数据库中是否有数据。

旁注：我不确定将这些存储为实例变量是个好主意。你应该真的返回Cursor或User对象。

应用程序按下按钮时崩溃

1 个答案: