Question

在我的Windows窗体中，我有2个文本框，即启动里程表读数和结束里程表读数。我的目标是从“结束阅读”中减去“开始阅读”，并在窗体表格标签中显示客户名称和电话号码旁边的标签中的差异。

如何返回方法getMilesCharge()的值并将其显示在confirmLabel上？

租车类代码

//A class that represents the Rental Agency Class.
namespace Assignment1
{
  partial class RentalAgencyClass
  {
    //instance variables
    public string customerName { get; set; }
    public string phoneNumber { get; set; }
    public double sMiles { get; set; }
    public double eMiles { get; set; }
    public double noOfDays { get; set; }
    private double DAY_CHARGE = 15;
    private double MILE_CHARGE = 0.12;

    //Constructor class
    //sets the value of the starting and ending miles.
    //sets the value of the number of days the car was rented for
    public RentalAgencyClass(double startMiles, double endMiles, double days)
    {
      startMiles = sMiles;
      endMiles = eMiles;
      days = noOfDays;
    }

    //method to calculate the number of miles driven on the rental
    public double getMileCharge()
    {
      double milesDriven = 0;
      milesDriven = eMiles - sMiles;
      return milesDriven * MILE_CHARGE;
    }

    //method to calculate the Day Charges on the rental
    public double getDayCharge()
    {
      return noOfDays * DAY_CHARGE;
    }

    //Property to display the information on the label
    public string GetInfo()
    {
      return customerName + " | " + phoneNumber + " | " + getDayCharge() +" miles";
    }
  }
}

表单设计器类代码

namespace Assignment1
{
  public partial class RentalAgencyClass : Form
  {
    RentalAgencyClass aCarRental;

    public RentalAgencyClass()
    {
      InitializeComponent();
    }

    private void calculateButton_Click(object sender, EventArgs e)
    {
      try
      {
        //instantiates object
        aCarRental = new RentalAgencyClass();
        aCarRental.customerName = nameTextBox.Text;
        aCarRental.phoneNumber = phoneTextBox.Text;
        //aCarRental. = getDayCharge();               
        // aCarRental.milesDriven = //store the difference in this variable
        //displayLabel.Text = "(student information saved)";
      }
      catch (Exception err)
      {
        MessageBox.Show(err.Message, "Error");
      }

      //Displays information about the Rental
      confirmLabel.Text = aCarRental.GetInfo();
    }
  }
}

Answer 1

通过在aCarRental = new RentalAgencyClass();方法中调用calculateButton_Click，您正在调用partial class RentalAgencyClass的无参数构造函数，这意味着在您的情况下，您正在创建表单的新实例而不是设置你的财产。因此sMiles和eMiles将保留其默认值0。

要使代码正常工作，您必须执行几个步骤。

首先，我建议您拆分表格和代理机构。因此，假设您将表单类重命名为RentalCalculator。下一步，您必须/可以从partial中移除RentalAgencyClass，因为它不再是您的表单类的一部分，我认为您不希望在另一部分扩展您的类你的代码。

正如LarsTech在评论中指出的那样。您现在应该将RentalAgencyClass构造函数修复为：

public RentalAgencyClass(double startMiles, double endMiles, double days)
{
    this.sMiles = startMiles;
    this.eMiles = endMiles;
    this.noOfDays = days;
}

并可以将以下属性添加到您的班级

public double milesDriven
{
    get
    { 
        return this.eMiles - this.sMiles;
    }
}

至少你必须改变你的事件处理程序：

private void calculateButton_Click(object sender, EventArgs e)
{
    try
    {
        // if not existing you have to create some input textboxes
        double startMiles = Convert.ToDouble(startMilesTextBox.Text);
        double endMiles = Convert.ToDouble(endMilesTextBox.Text);
        double days = Convert.ToDouble(daysTextBox.Text);

        // Hint: you are creating a new instance on every button click 
        //       and overwriting your field in your form class. 
        aCarRental = new RentalAgencyClass(startMiles, endMiles, days);
        aCarRental.customerName = nameTextBox.Text;
        aCarRental.phoneNumber = phoneTextBox.Text;

        // Store the result in local variables
        // if you want to do something with them later
        double dayCharge = aCarRental.getDayCharge();
        double milesCharge = aCarRental.getMilesCharge();               
        double drivenMiles = aCarRental.milesDriven;

        // displayLabel.Text = "(student information saved)";
    }
    catch (Exception err)
    {
        MessageBox.Show(err.Message, "Error");
    }

    //Displays information about the Rental
    confirmLabel.Text = aCarRental.GetInfo();
}

回答你的问题：

如何返回方法getMilesCharge()的值并将其显示在confirmLabel上？

您必须在calculateButton_Click方法中更改以下行：

confirmLabel.Text = aCarRental.GetInfo();

为：

confirmLabel.Text = aCarRental.getMilesCharge().ToString();

最后但并非最不重要的是，让我给你一个善意的建议您可以查看Microsoft Naming Guidelines 例如：属性应在PascalCasing中命名但这只是我个人的意见。

返回get set方法值到label

1 个答案: