Android：尝试在空对象引用上调用虚拟方法“void android.database.sqlite.SQLiteDatabase.execSQL(java.lang.String)”[重复]

Question

我收到此错误：

无法开始活动 组件信息{amsi.dei.estg.ipleiria.pt.ima/amsi.dei.estg.ipleiria.pt.ima.ListaEmpresas}： java.lang.NullPointerException：尝试调用虚拟方法'void android.database.sqlite.SQLiteDatabase.execSQL(java.lang.String)' 在一个 空对象引用”在我的 DBHelper 中的这一行：

错误在这一行：

database.execSQL(createEmpresasTable);

我的 DBHelper：

public class ImaBDHelper extends SQLiteOpenHelper {

private static final String DB_NAME = "IMA";
private static final int DB_VERSION = 1;

private static final String EMPRESAS_TABLE_NAME = "empresas";
private static final String NOME_EMPRESA = "nome";
private static final String DESCRICAO_EMPRESA = "descricao";
private static final String LOCALIDADE_EMPRESA = "localidade";
private static final String AREA_EMPRESA = "area";

private final SQLiteDatabase database;

public ImaBDHelper(Context context)
{
    super(context, DB_NAME, null, DB_VERSION);

    this.database = getWritableDatabase();
}


@Override
public void onCreate(SQLiteDatabase db) {
    String createEmpresasTable = "CREATE TABLE " + EMPRESAS_TABLE_NAME +
            "(id INTENGER PRIMARY KEY AUTOINCREMENT," +
            NOME_EMPRESA + " TEXT NOT NULL," +
            DESCRICAO_EMPRESA + " TEXT," +
            LOCALIDADE_EMPRESA + " TEXT NOT NULL," +
            AREA_EMPRESA + " TEXT NOT NULL," + ")";
database.execSQL(createEmpresasTable);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    String sql = "DROP TABLE IF EXISTS " + EMPRESAS_TABLE_NAME;
    database.execSQL(sql);
    this.onCreate(database);
}

其余的只是创建、读取、更新和删除的方法。

对不起，如果这是重复的，但我在搜索中没有找到这个确切问题的答案。提前谢谢！

Answer 1

使用onCreate(SQLiteDatabase db) 签名值代替private final SQLiteDatabase database; 执行如下查询

@Override
public void onCreate(SQLiteDatabase db) {
    String createEmpresasTable = "CREATE TABLE " + EMPRESAS_TABLE_NAME +
            "(id INTENGER PRIMARY KEY AUTOINCREMENT," +
            NOME_EMPRESA + " TEXT NOT NULL," +
            DESCRICAO_EMPRESA + " TEXT," +
            LOCALIDADE_EMPRESA + " TEXT NOT NULL," +
            AREA_EMPRESA + " TEXT NOT NULL," + ")";
db.execSQL(createEmpresasTable);// change here
}

这样也可以在你的 onUpgrade() 中使用