Question

我写了一些测试BankAccount的代码，我完成了它（大部分）。我的目的是试图学习如何抛出和尝试/捕获异常。在大多数情况下，我学到了很多东西。我意识到这不是一个“例外”的案例，if / else语句会更合适。我只是想学习异常处理。我试图编写异常类来扩展一个类，以包含一个新的消息，详细说明抛出异常时发送的错误。我读了一下超类是什么，或者是c＃中的基类，并试了一下。它编译并看起来正确，但我不知道我做错了什么。有人可以向我解释为什么我的抛出新的NegativeDepositException中的消息不会显示。

我想要它做的是抛出一条消息，而不是在MessageBox.Show中放一个字符串。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
public partial class Form1 : Form
{
        public class NegativeBalanceException : Exception { }
        public class NegativeWithdrawException : Exception { }
        public class NegativeDepositException : Exception
        {
            public NegativeDepositException() { } // this  doesn't do what I would like for it to do.
            public NegativeDepositException(string message)
                : base(message) { }
        }
    public Form1()
    {
        InitializeComponent();
    }
    public class BankAccount
    {
        decimal amount = 300.00m;
        // Declare Delegate Type Object
        public delegate void BankDelegate(decimal oldBalance, decimal newBalance);
        // Create Delegate Type Events 
        public event BankDelegate OnDeposit;
        public event BankDelegate OnWithdraw;

        public void Deposit(decimal a)
        {
            if (a < 0)
                throw new NegativeDepositException(); //"type some message here instead of messagebox below");
            OnDeposit(this.amount, this.amount + a);
            this.amount += a;
        }
        public void Withdraw(decimal a)
        {
            if (a < 0)
                throw new NegativeWithdrawException();
            OnWithdraw(this.amount, this.amount - a);
            this.amount -= a;
            if (this.amount < 0)
                throw new NegativeBalanceException();
        }
    }
    // this is my bank class variable...
    BankAccount account = null;
    private void Form1_Load(object sender, EventArgs e)
    {
      account = new BankAccount();
        account.OnDeposit += new BankAccount.BankDelegate(account_OnDeposit);
        account.OnWithdraw += new BankAccount.BankDelegate(account_OnWithdraw);
    }
    private void btnDeposit_Click(object sender, EventArgs e)
    {
        {
            var amount = Convert.ToDecimal(textBox1.Text);
            try { account.Deposit(amount); }
            catch (NegativeDepositException)
            {
                MessageBox.Show("Cannot deposit negative amounts");
            }
        }
    }
    private void btnWIthdraw_Click(object sender, EventArgs e)
    {
        var amount = Convert.ToDecimal(textBox1.Text);
        try { account.Withdraw(amount); }
        catch (NegativeBalanceException)
        {
            MessageBox.Show("Cannot withdraw money that isn't there");
        }
        catch (NegativeWithdrawException)
        {
            MessageBox.Show("Cannot withdraw negative money");
        }
    }
    void account_OnDeposit(decimal oldBalance, decimal newBalance)
    {
        label4.Text = oldBalance.ToString();
        label5.Text = newBalance.ToString();
    }
    void account_OnWithdraw(decimal oldBalance, decimal newBalance)
    {
        label4.Text = oldBalance.ToString();
        label5.Text = newBalance.ToString();
    }
}

Answer 1

也许我误解了这个问题，但是在抛出异常时你没有传递消息;

应该是：

 if (a < 0)
    throw new NegativeDepositException("Cannot deposit negative amounts");

并且在捕获它时需要调用Exception的Message属性（在Exception基类中）

    catch (NegativeWithdrawException exception)
    {
        MessageBox.Show(exception.Message);
    }

在异常中显示消息

1 个答案: