尝试调用虚方法 'long android.database.sqlite.SQLite

Question

我正在开发 android 项目并获取空对象引用

数据库助手类

package com.example.smartpmr;

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 {

    // DATABASE NAME

    private static final String DATABASE_NAME = "PMR";

    // DATABASE VERSION

    private static final int DATABASE_VERSION = 1;

    // PATIENT TABLE

    private static final String TABLE_PATIENT = "tblPatient";

    // DOCTOR TABLE

    private static final String TABLE_DOCTOR = "tblDoctor";

    // PRESCRIPTION TABLE

    private static final String TABLE_PRESCRIPTION = "tblPrescription";

    // MEDICINE TABLE

    private static final String TABLE_MEDICINES = "tblMedicines";

    // PATIENT TABLE COLUMNS

    public static final String PATIENT_ID = "PATIENT_ID";

    public static final String PATIENT_NAME = "PATIENT_NAME";

    public static final String PATIENT_EMAIL = "PATIENT_EMAIL";

    public static final String PATIENT_PASSWORD = "PATIENT_PASSWORD";

    public static final String PATIENT_AGE = "PATIENT_AGE";

    public static final String PATIENT_CONTACT = "PATIENT_CONTACT";

    public static final String PATIENT_ADDRESS = "PATIENT_ADDRESS";

    // DOCTOR TABLE COLUMS

    public static final String DOCTOR_ID = "DOCTOR_ID";

    public static final String DOCTOR_NAME = "DOCTOR_NAME";

    public static final String DOCTOR_EMAIL = "DOCTOR_EMAIL";

    public static final String DOCTOR_PASSWORD = "DOCTOR_PASSWORD";

    public static final String DOCTOR_CONTACT = "DOCTOR_CONTACT";

Answer 1

您没有db在方法中初始化insertPrescription()并且saveMedicine()（就像您在其他方法中正确执行的那样）：db = this.getWritableDatabase();所以db当你使用它时它是空的。