调用对象的实例

Question

我有一个让我非常困惑的问题。在我的类的构造函数中，我创建了一个 SeatManager.cs 实例，它包含两个数组（字符串和双精度）。在方法 btnReserveCancel_Click 中，我尝试用数据填充这两个数组。但是，当我稍后调用 UpdateGUI() 方法时，会创建 SeatManager.cs 的另一个实例（当我需要帮助处理另一件事时，我的老师添加了该行代码），当发生这种情况时，我刚刚填充两个数组的所有数据都会得到丢失的！奇怪的是，如果我删除在 UpdateGUI() 中创建新实例的行，编译器会向我大喊有问题。

为什么 UpdateGUI() 需要 SeatManager.cs 的新实例，而 btnReserveCancel_Click 不需要？当实例变量中有一个可用的 SeatManager.cs 实例时，为什么 UpdateGUI() 需要一个新的 SeatManager.cs 实例？

    private double revenue = 0.0;
    private const int totalNumOfSeats = 10;
    private int numOfReservedSeats = 0; //Increases every time a new reservation is made
    const double minLimit = 10;
    const double maxLimit = 50;
    private SeatManager seatMngr;

    public MainForm()
    {
        InitializeComponent();
        InitializeGUI();
        seatMngr = new SeatManager(totalNumOfSeats);//skapar en instans av klassen SeatManager
        UpdateGUI();
    }



    private void btnReserveCancel_Click(object sender, EventArgs e)
    {
        if (rbtnReserved.Checked == true)//Om radiobutton RESERVE är iklickad
        {
            string customerName = string.Empty;
            double seatPrice = 0.0;

            int selection = listBox1.SelectedIndex;
            if (selection == -1)
            {
                MessageBox.Show(string.Format("You must select which seat you want to reserve!"), "Select a seat.", MessageBoxButtons.OK, MessageBoxIcon.None);

            }
            else
            {
                string getSeatNumber = listBox1.SelectedItem.ToString();//Tar första bokstaven i den markerade strängen i listboxen och gör om till index.
                int seatNumber = int.Parse(getSeatNumber.Substring(0, 1));

                bool inputOk = ReadAndValidateInput(out customerName, out seatPrice);
                bool validSeats = CheckVacantSeats();

                if (inputOk && validSeats)
                {
                    if (seatMngr.ReserveSeat(customerName, seatPrice, seatNumber) != true)
                    {
                        var result = MessageBox.Show(string.Format("Do you wish to overwrite reservation? "), "Seat already registered", MessageBoxButtons.YesNo, MessageBoxIcon.None);
                        if (result == DialogResult.Yes)
                        {
                            double amount = seatMngr.GetPaidPrice(seatNumber);
                            MoneyBackWhenCancelOrOverwrite(amount);
                            seatMngr.ReserveSeatOverwrite(customerName, seatPrice, seatNumber);
                            revenue += seatPrice;
                        }
                    }
                    else
                    {
                        seatMngr.ReserveSeat(customerName, seatPrice, seatNumber);
                        numOfReservedSeats++;
                        revenue += seatPrice;
                        if (seatMngr.ReserveSeat(customerName, seatPrice, seatNumber) == true)
                        {
                            MessageBox.Show(string.Format("Det funkade "), "Sfgdfg", MessageBoxButtons.OK, MessageBoxIcon.None);
                        }
                    }
                }
            }
        }
        else if (rbtnCancel.Checked == true)//Om radiobutton CANCEL är iklickad.
        {
            string getSeatNumber = listBox1.SelectedItem.ToString();//Tar första bokstaven i den markerade strängen i listboxen och gör om till index.
            int seatNumber = int.Parse(getSeatNumber.Substring(0, 1));

            var result = MessageBox.Show(string.Format("Do you wish to cancel reservation? "), "Seat registered", MessageBoxButtons.YesNo, MessageBoxIcon.None);
            if (result == DialogResult.Yes)
            {
                double amount = seatMngr.GetPaidPrice(seatNumber);
                MoneyBackWhenCancelOrOverwrite(amount);
                seatMngr.CancelSeat(seatNumber);
                numOfReservedSeats--;
            }
            else { }
        }
        UpdateGUI();
    }



    private void UpdateGUI()
    {
        labelVacant.Text = (totalNumOfSeats - numOfReservedSeats).ToString();//Visar antal ledig platser.
        labelReserved.Text = numOfReservedSeats.ToString();//Visar antal reserverade platser.
        labelRevenue.Text = revenue.ToString();//Visar intäkter.
        labelSeats.Text = totalNumOfSeats.ToString();//Visar totalt antal platser. Värdet är konstant så det kan inte ändras.
        DisplayOptions choice = (DisplayOptions)comboBox1.SelectedIndex;

        string[] strSeatInfoStrings;


        //seatMngr = new SeatManager(totalNumOfSeats);

        int display = seatMngr.GetSeatInfoStrings(choice, out strSeatInfoStrings);
        listBox1.Items.Clear();
        if (strSeatInfoStrings == null)
        {
            listBox1.Items.Add("No seats where found");
        }
        else
        {
            listBox1.Items.AddRange(strSeatInfoStrings);
        }
    }

Answer 1

如果您有一个指向内存中对象的引用，然后为它分配一个新实例，则它之前指向的对象将“丢失”（假设不再有对它的引用）并最终被垃圾收集。这就是为什么当您在 UpdateGUI() 中创建新实例时会丢失所有先前填充的数据。

如果您计划跨方法调用维护状态，则正确的版本显然没有新的实例化。如果删除该行，会出现什么编译器错误？

编辑：当您声明 SeatMngr 时，尝试同时进行实例化并将其从构造函数中删除：

private SeatManager seatMng = new SeatManager(totalNumOfSeats);

Answer 2

您需要发布 SeatManager 类的代码，否则很难知道发生了什么。现在，除非当前注释掉的行：

//seatMngr = new SeatManager(totalNumofSeats);

未注释，否则我目前没有看到问题。