c# - InterestRate 正在返回 0，我使用的引用来自另一个 Form

Question

我是 C# 的新手，今天我已经在这里发过一次帖，非常感谢能得到的所有帮助!我有一个用 Visual Basic 创建的程序。该表单有一个主表单 - AccountForm.cs，三个副表单 - WithdrawlForm.cs、DepositForm.cs 和 InterestForm.cs。我有两个类，Account.cs 及其派生类 SavingsAccount.cs。我正在尝试将下面字符串中的 InterestRate 更改为用户在 InterestForm 上输入的利率。此代码位于 SavingsAccount 类 .cs 文件中。

     public new string toString()
    {
        return String.Format("Account Number: {0} Balance: {1:C} Interest Rate: {2:P}", AccountNumber, AccountBalance, InterestRate);
    }  

完整的 SavingsAccount.cs 文件

namespace Assignment_6_third_attempt
{
public class SavingsAccount : Account
{
    private InterestForm interestForm = new InterestForm();

    private double interestRate = 0.0;

    #region Constructors
    public SavingsAccount(int accountNumber)
    {
        base.accountNumber = accountNumber;
    }

    public SavingsAccount() { }
    #endregion

   double InterestRate 
   {
        get { return interestForm.interestRate ; }
        set { interestRate = interestForm.interestRate; }
    }

    public double Interest(double amount)
    {
        InterestRate = interestForm.interestRate;
        return InterestRate;          
    }


    public void AddInterest(double amount)
    {
        //interestForm.CalculateInterest();
        AccountBalance = amount;
    }


    public new string toString()
    {
        return String.Format("Account Number: {0} Balance: {1:C} Interest Rate: {2:P}", AccountNumber, AccountBalance, InterestRate);
    }       
}
}

这是我的 AccountForm.cs 文件(此表单是主表单，其中显示了帐号、账户余额和利率。

 namespace Assignment_6_third_attempt
{
public partial class AccountForm : Form
{
    SavingsAccount savingsAccount;
    public System.Windows.Forms.Label labelInformation;

    public AccountForm()
    {
        InitializeComponent();
        labelInformation = accountInfoLabel;
    }

    private void createAccountButton_Click(object sender, EventArgs e)
    {
        Random random = new Random();
        int newAccountNumber = random.Next(0, 1000000);
        savingsAccount = new SavingsAccount(newAccountNumber);

        MessageBox.Show(savingsAccount.toString());
        accountInfoLabel.Text = savingsAccount.toString();
        depositButton.Enabled = true;
        withdrawalButton.Enabled = true;
        interestButton.Enabled = true;
    }

    private void depositButton_Click(object sender, EventArgs e)
    {
        DepositForm depForm = new DepositForm();
        depForm.ShowDialog();
        savingsAccount.Deposit((double)depForm.DepositAmount);
        accountInfoLabel.Text = savingsAccount.toString();
    }

    private void withdrawalButton_Click(object sender, EventArgs e)
    {
        try
        {
            WithdrawalForm withdrawForm = new WithdrawalForm();
            withdrawForm.ShowDialog();
            savingsAccount.Withdraw((double)withdrawForm.WithdrawAmount);
            accountInfoLabel.Text = savingsAccount.toString();
        }
        catch (InvalidOperationException ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    private void closeAccountButton_Click(object sender, EventArgs e)
    {
        depositButton.Enabled = false;
        withdrawalButton.Enabled = false;
        accountInfoLabel.Text = "";

        savingsAccount = null; //this will clean it up off the heap.
    }



    private void interestButton_Click(object sender, EventArgs e)
    {
        InterestForm interestForm = new InterestForm(savingsAccount.AccountBalance);
        interestForm.ShowDialog();
        savingsAccount.AddInterest(interestForm.CalculateInterest());           
        accountInfoLabel.Text = savingsAccount.toString();
        savingsAccount.Interest(interestForm.interestRate);
        accountInfoLabel.Text = savingsAccount.toString();
        }


    }
}

最后，这是我的 InterestForm.cs 代码，用户可以在其中在 NumericUpDown 控件中输入术语和比率。

 namespace Assignment_6_third_attempt
{
 public partial class InterestForm : Form
{

    private Account account = new Account();
    //private double accountBalance;
    public double interestRate = 0.0;

    public InterestForm()
    {
        InitializeComponent();
    }


    public InterestForm(double accountBalance) : this()
    {

        //InitializeComponent();
        account.AccountBalance = accountBalance;
    }


    private void addInterestButton_Click(object sender, EventArgs e)
    {
        double interestRate = double.Parse(interestUpDown.Text);
        CalculateInterest();
        this.Close();
    }



    public double CalculateInterest()
    {
        //A = P(1 + rt)
        double accountBalance = account.AccountBalance;            
        double interestRate = (double)interestUpDown.Value;
        double term = (double)termUpDown.Value;
        double estimateInterest = (accountBalance * (1 + (interestRate * term)));
        return estimateInterest;
    }


}
}

Answer 1

编辑:

除了提到的所有 原始问题外，您似乎混淆了 interestRate 的范围private 字段 interestRate 局部变量在这里:

private void addInterestButton_Click(object sender, EventArgs e)
{
    double interestRate = double.Parse(interestUpDown.Text); //this is local variable!!
    CalculateInterest();
    this.Close();
}

请注意，您使用本地 interestRate ，不是你的类(class)'interestRate .同样，要注意变量的范围。局部变量不能全局访问，如果在局部方法中有相同的变量名，则必须将其与使用 this 的全局变量(类'字段)区分开来关键字(this.VariableName 是字段，但 VariableName 是本地的)。

在您上面的例子中，只需使用 class领域 interestRate而不是定义新的局部变量 interestRate :

private void addInterestButton_Click(object sender, EventArgs e)
{
    interestRate = double.Parse(interestUpDown.Text); //remove the double
    CalculateInterest();
    this.Close();
}

原文:

setter和 getter的 InterestRate似乎...不对称:

double InterestRate 
{
    get { return interestForm.interestRate ; } //you get from other form
    set { interestRate = interestForm.interestRate; } //and you set from other form
}

你得到 interestForm.interestRate来自其他表格并将其设置为 interestRate在你的Form但你从不使用本地 interestRate .将其更改为:

double InterestRate 
{
    get { return interestRate ; }
    set { interestRate = value; }
}

您的 Interest 也是如此:

public double Interest(double amount)
{
    InterestRate = interestForm.interestRate;
    return InterestRate;          
}

您再次使用您的私有(private) Form除了被构造之外，它在类中未被使用。使用你的 amount相反:

public double Interest(double amount)
{
    InterestRate = amount; //change into this
    return InterestRate;          
}

现在，还要注意:

private void interestButton_Click(object sender, EventArgs e)
{
    InterestForm interestForm = new InterestForm(savingsAccount.AccountBalance);
    interestForm.ShowDialog();
    savingsAccount.AddInterest(interestForm.CalculateInterest());           
    accountInfoLabel.Text = savingsAccount.toString();
    savingsAccount.Interest(interestForm.interestRate);
    accountInfoLabel.Text = savingsAccount.toString();
}

你有 InterestForm在那里声明，但它是一个 new InterestForm , 这不是你的 private InterestForm在你的SavingAccount .简而言之，InterestForm你声明和InterestForm在你的SavingAccount是两个不同的表单实例，尽管它们共享相同的名称 interestForm .查看访问修饰符 - 不是实例的名称 - 以了解您的 object 的范围.

也就是说，上面的设计使用非字段InterestForm填满你的兴趣就可以了。我什至会说，使用 private InterestForm不需要。您只需要将值传递给外部 InterestForm有你的SavingAccount实例，不创建私有(private) InterestForm为你的 SavingAccount