Winforms 如何实现自动售货机？

对于一个学校项目，我被要求使用VisualBasic在windows窗体应用程序中创建一个虚拟自动售货机。我大约完成了80%，但我有一些问题，我已经研究了多次，但仍然找不到帮助

首先，在自动售货机上，当我购买商品时，如果剩余（更改）的信用低于产品的原始价格，它将显示一条错误消息，说明您没有足够的信用来购买产品。如果信用卡不足以在购买前购买产品，而不是在购买后立即购买产品，我如何使其仅显示该消息

其次，我将如何着手为购买后剩余的信用创建一个系统，因为目前我只有一个信用返回按钮，用户将使用该按钮提取购买后剩余的信用，而不是一个用于支付零钱的系统

最后，我如何使用户不被允许在文本框中输入文本，因为自动售货机使用两个文本框，一个显示信用，另一个显示其他一般消息，例如澄清您购买了某个产品或您没有足够的信用购买某个产品

以下是我目前的代码：

Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    RichTextBox1.Text = "You Have Selected Galaxy Caramel, Please Insert 60p"
    If credit >= 60 Then RichTextBox1.Text = "Thank you for purchasing a Galaxy Caramel bar"
    credit = credit - 60
    TextBox1.Text = credit
    If credit < 60 Then RichTextBox1.Text = "You do not have enough credit to purchase a Galaxy Caramel Bar"



End Sub

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
    RichTextBox1.Text = "You Have Selected Cadburys Milk Chocolate, Please Insert 75p"
    If credit >= 75 Then RichTextBox1.Text = "Thank you for purchasing a Cadburys Milk Chocolate Bar"
    credit = credit - 75
    TextBox1.Text = credit
    If credit < 75 Then RichTextBox1.Text = "You do not have enough credit to purchase a Cadburys Milk Chocolate Bar"
End Sub

Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
    RichTextBox1.Text = "You Have Selected Bounty, Please Insert 70p"
    If credit >= 70 Then RichTextBox1.Text = "Thank you for purchasing a Bounty bar"
    credit = credit - 70
    TextBox1.Text = credit
    If credit < 70 Then RichTextBox1.Text = "You do not have enough credit to purchase a Bounty Bar"



End Sub

Private Sub Button4_Click(sender As System.Object, e As System.EventArgs) Handles Button4.Click
    RichTextBox1.Text = "You Have Selected Yorkie, Please Insert 60p"
    If credit >= 60 Then RichTextBox1.Text = "Thank you for purchasing a Yorkie bar"
    credit = credit - 60
    TextBox1.Text = credit
    If credit < 60 Then RichTextBox1.Text = "You do not have enough credit to purchase a Yorkie Bar"




End Sub

Private Sub Button8_Click(sender As System.Object, e As System.EventArgs) Handles Button8.Click
    RichTextBox1.Text = "You Have Selected Doritos Tangy Cheese, Please Insert 85p"
    If credit >= 85 Then RichTextBox1.Text = "Thank you for purchasing Doritos Tangy Cheese Crisps"
    credit = credit - 85
    TextBox1.Text = credit
    If credit < 85 Then RichTextBox1.Text = "You do not have enough credit purchase Doritos Tangy Cheese Crisps"



End Sub

Private Sub Button7_Click(sender As System.Object, e As System.EventArgs) Handles Button7.Click
    RichTextBox1.Text = "You Have Selected Doritos Cool Original, Please Insert 75p"
    If credit >= 75 Then RichTextBox1.Text = "Thank you for purchasing Doritos Cool Original Crisps"
    credit = credit - 75
    TextBox1.Text = credit
    If credit < 75 Then RichTextBox1.Text = "You do not have enough credit to purchase Doritos Cool Original Crisps"

End Sub

Private Sub Button6_Click(sender As System.Object, e As System.EventArgs) Handles Button6.Click
    RichTextBox1.Text = "You Have Selected Walkers Cheese & Onion, Please Insert 70p"
    If credit >= 70 Then RichTextBox1.Text = "Thank you for purchasing Walkers Cheese & Onion Crisps"
    credit = credit - 70
    TextBox1.Text = credit
    If credit < 70 Then RichTextBox1.Text = "You do not have enough credit to purchase Walkers Cheese & Onion Crisps"


End Sub

Private Sub Button5_Click(sender As System.Object, e As System.EventArgs) Handles Button5.Click
    RichTextBox1.Text = "You Have Selected Mccoy's Cheddar, Please Insert 80p"
    If credit >= 80 Then RichTextBox1.Text = "Thank you for purchasing Mccoy's Cheddar Crisps"
    credit = credit - 80
    TextBox1.Text = credit
    If credit < 80 Then RichTextBox1.Text = "You do not have enough credit to purchase Mccoy's Cheddar Crisps"


End Sub

Private Sub Button9_Click(sender As System.Object, e As System.EventArgs) Handles Button9.Click
    RichTextBox1.Text = "You Have Selected Pepsi Max, Please Insert £1.10"
    If credit >= 110 Then RichTextBox1.Text = "Thank you for purchasing Pepsi Max"
    credit = credit - 110
    TextBox1.Text = credit
    If credit < 110 Then RichTextBox1.Text = "You do not have enough credit to purchase Pepsi Max"


End Sub

Private Sub Button12_Click(sender As System.Object, e As System.EventArgs) Handles Button12.Click
    RichTextBox1.Text = "You Have Selected Mountain Dew, Please Insert 99p"
    If credit >= 99 Then RichTextBox1.Text = "Thank you for purchasing Mountain Dew"
    credit = credit - 99
    TextBox1.Text = credit
    If credit < 99 Then RichTextBox1.Text = "You do not have enough credit to purchase Mountain Dew"

End Sub

Private Sub Button10_Click(sender As System.Object, e As System.EventArgs) Handles Button10.Click
    RichTextBox1.Text = "You Have Selected Fanta, Please Insert £1.05"
    If credit >= 105 Then RichTextBox1.Text = "Thank you for purchasing Fanta"
    credit = credit - 105
    TextBox1.Text = credit
    If credit < 105 Then RichTextBox1.Text = "You do not have enough credit to purchase Fanta"

End Sub

Private Sub Button11_Click(sender As System.Object, e As System.EventArgs) Handles Button11.Click
    RichTextBox1.Text = "You Have Selected Dr.Pepper, Please Insert £1.20"
    If credit >= 120 Then RichTextBox1.Text = "Thank you for purchasing Dr.Pepper"
    credit = credit - 120
    TextBox1.Text = credit
    If credit < 120 Then RichTextBox1.Text = "You do not have enough credit to purchase Dr.Pepper"

End Sub

Private Sub Button13_Click(sender As System.Object, e As System.EventArgs) Handles Button13.Click
    RichTextBox1.Text = "You Have Selected Buxton Mineral Water, Please Insert 90p"
    If credit >= 90 Then RichTextBox1.Text = "Thank you for purchasing Buxton Mineral Water"
    credit = credit - 90
    TextBox1.Text = credit
    If credit < 90 Then RichTextBox1.Text = "You do not have enough credit to purchase Buxton Mineral Water"
End Sub

Private Sub Button14_Click(sender As System.Object, e As System.EventArgs) Handles Button14.Click
    credit = credit + 1
    TextBox1.Text = credit
End Sub

Private Sub Button21_Click(sender As System.Object, e As System.EventArgs) Handles Button21.Click
    credit = credit + 2
    TextBox1.Text = credit
End Sub

Private Sub Button20_Click(sender As System.Object, e As System.EventArgs) Handles Button20.Click
    credit = credit + 5
    TextBox1.Text = credit
End Sub

Private Sub Button19_Click(sender As System.Object, e As System.EventArgs) Handles Button19.Click
    credit = credit + 10
    TextBox1.Text = credit
End Sub

Private Sub Button18_Click(sender As System.Object, e As System.EventArgs) Handles Button18.Click
    credit = credit + 20
    TextBox1.Text = credit
End Sub

Private Sub Button17_Click(sender As System.Object, e As System.EventArgs) Handles Button17.Click
    credit = credit + 50
    TextBox1.Text = credit
End Sub

Private Sub Button16_Click(sender As System.Object, e As System.EventArgs) Handles Button16.Click
    credit = credit + 100
    TextBox1.Text = credit
End Sub

Private Sub Button15_Click(sender As System.Object, e As System.EventArgs) Handles Button15.Click
    credit = credit + 200
    TextBox1.Text = credit
End Sub

Private Sub Button22_Click(sender As System.Object, e As System.EventArgs) Handles Button22.Click
    credit = 0
    TextBox1.Text = credit
    RichTextBox1.Text = "Credit has been returned"
End Sub

Private Sub TextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles TextBox1.TextChanged
    If credit < 0 Then credit = 0
    TextBox1.Text = credit


    If credit >= 1000 Then credit = 1000
    TextBox1.Text = credit
    If credit = 1000 Then RichTextBox1.Text = "Maximum credit of £10"
End Sub

Private Sub Button23_Click(sender As System.Object, e As System.EventArgs) Handles Button23.Click
    RichTextBox1.Text = "You Have Selected Monster Munch, Please Insert 90p"
    If credit >= 90 Then RichTextBox1.Text = "Thank you for purchasing Monster Munch Crisps"
    credit = credit - 90
    TextBox1.Text = credit
    If credit < 90 Then RichTextBox1.Text = "You do not have enough credit to purchase Monster Munch Crisps"


End Sub

Private子按钮1\u单击（发送方作为System.Object，e作为System.EventArgs）处理按钮1。单击
RichTextBox1.Text=“您已选择Galaxy焦糖，请插入60p”
如果信用>=60，则RichTextBox1.Text=“感谢您购买Galaxy焦糖棒”
信用=信用-60
TextBox1.Text=信用卡
如果信用<60，则RichTextBox1.Text=“您没有足够的信用购买Galaxy焦糖棒”
端接头
私有子按钮2\u单击（发送者作为System.Object，e作为System.EventArgs）处理按钮2。单击
RichTextBox1.Text=“您已选择Cadburys牛奶巧克力，请插入75便士”
如果信用>=75，则RichTextBox1.Text=“感谢您购买Cadburys牛奶巧克力”
信用=信用-75
TextBox1.Text=信用卡
如果信用<75，则RichTextBox1.Text=“您没有足够的信用购买Cadburys牛奶巧克力”
端接头
私有子按钮3\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮3。单击
RichTextBox1.Text=“您已选择赏金，请插入70便士”
如果信用>=70，则RichTextBox1.Text=“感谢您购买赏金吧”
信用=信用-70
TextBox1.Text=信用卡
如果信用<70，则RichTextBox1.Text=“您没有足够的信用购买赏金条”
端接头
私有子按钮4\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮4。单击
RichTextBox1.Text=“您已选择Yorkie，请插入60p”
如果信用>=60，则RichTextBox1.Text=“感谢您购买约克酒吧”
信用=信用-60
TextBox1.Text=信用卡
如果信用<60，则RichTextBox1.Text=“您没有足够的信用购买约克酒吧”
端接头
私有子按钮8\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮8。单击
RichTextBox1.Text=“您已选择多丽托斯浓烈奶酪，请插入85便士”
如果信用>=85，则RichTextBox1.Text=“感谢您购买多力多司香脆奶酪”
信用=信用-85
TextBox1.Text=信用卡
如果信用<85，则RichTextBox1.Text=“您没有足够的信用购买多力多滋味奶酪薯片”
端接头
私有子按钮7\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮7。单击
RichTextBox1.Text=“您已选择Doritos Cool Original，请插入75p”
如果信用>=75，则RichTextBox1.Text=“感谢您购买Doritos Cool原创薯片”
信用=信用-75
TextBox1.Text=信用卡
如果信用度<75，则RichTextBox1.Text=“您没有足够的信用度购买Doritos Cool Original Crisps”
端接头
私有子按钮6\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮6。单击
RichTextBox1.Text=“您已选择Walkers奶酪和洋葱，请插入70便士”
如果信用>=70，则RichTextBox1.Text=“感谢您购买Walkers奶酪和洋葱薯片”
信用=信用-70
TextBox1.Text=信用卡
如果信用<70，则RichTextBox1.Text=“您没有足够的信用购买Walkers奶酪和洋葱薯片”
端接头
私有子按钮5\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮5。单击
RichTextBox1.Text=“您选择了Mccoy的切达干酪，请插入80便士”
如果信用>=80，则RichTextBox1.Text=“感谢您购买麦考伊的切达薯片”
信用=信用-80
TextBox1.Text=信用卡
如果信用<80，则RichTextBox1.Text=“您没有足够的信用购买Mccoy的切达薯片”
端接头
私有子按钮9\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮9。单击
RichTextBox1.Text=“您已选择百事Max，请插入1.10英镑”
如果信用>=110，则RichTextBox1.Text=“感谢您购买百事Max”
信用=信用-110
TextBox1.Text=信用卡
如果信用<110，则RichTextBox1.Text=“您没有足够的信用购买百事Max”
端接头
私有子按钮12\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮12。单击
RichTextBox1.Text=“您已选择Mountain Dew，请插入99p”
如果信用>=99，则RichTextBox1.Text=“感谢您购买Mountain Dew”
信用=信用-99
TextBox1.Text=信用卡
如果信用<99，则RichTextBox1.Text=“您没有足够的信用购买Mountain Dew”
端接头
私有子按钮10\u单击（发件人作为System.Object，e作为System.EventArgs）处理按钮10。单击
RichTextBox1.Text=“您已选择芬达，请插入1.05英镑”
如果信用>=105，则RichTextBox1.Text=“感谢您购买芬达”
信用=信用-105
TextBox1.Text=信用卡
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    RichTextBox1.Text = "You Have Selected Galaxy Caramel, Please Insert 60p"
    If credit >= 60 Then
        RichTextBox1.Text = "Thank you for purchasing a Galaxy Caramel bar"
        credit = credit - 60
        TextBox1.Text = credit
    Else
        RichTextBox1.Text = "You do not have enough credit to purchase a Galaxy Caramel Bar"
    End If
End Sub

    /// <summary>
    /// This method attempts to calculate required change from a given coin inventory
    /// </summary>
    /// <param name="coinInventory">Key is the denomination of coin and value is the available number </param>
    /// <param name="changeRequired">The change to count and return</param>
    /// <param name="updatedCoinInventory"></param>
    /// <param name="coinsToReturn"></param>
    /// <returns>True if changeRequired could be calculated, False if coinsToReturn represent less than changeRequired </returns>
    public bool GetChange(IDictionary<int, int> coinInventory, int changeRequired, 
                          ref IDictionary<int, int> updatedCoinInventory, 
                          ref IDictionary<int, int> coinsToReturn,
                          ref int amountDue) 
    {
        int changeOutstanding = changeRequired;

        updatedCoinInventory = coinInventory.ToDictionary(kvp => kvp.Key, kvp => kvp.Value); 

        coinsToReturn = new Dictionary<int, int>();

        foreach (KeyValuePair<int, int> coin in coinInventory)
        {
            if (changeOutstanding == 0) break;

            int numberOfAvailableCoins = coin.Value;

            while (changeOutstanding >= coin.Key && numberOfAvailableCoins >= 1)
            {
                if (!coinsToReturn.ContainsKey(coin.Key))
                {
                    coinsToReturn.Add(coin.Key, 1);
                }
                else
                {
                    ++ coinsToReturn[coin.Key];
                }

                changeOutstanding = changeOutstanding - coin.Key;

                -- updatedCoinInventory[coin.Key];
                -- numberOfAvailableCoins;
            }
        }

        amountDue = changeOutstanding;

        return changeOutstanding == 0;
    }

}