C# 如何构造从表单控件值获取参数的类对象？

我是C#的新手。我试图使用构造函数实例化一个对象，该对象从表单控件（NumericUpDown和两个复选框）获取参数

通常我在generate Form类中实例化对象，但当我尝试从表单控件传递值时，它会说它无法访问它们

我在InitializeComponent（）下有相同的实例化；但这并没有创建对象

namespace DinnerParty
{
    public partial class Form1 : Form
    {


    //Usually instantiate here, but in this case my constructor is taking input from the control on the form. I'm getting errors saying it cant
    DinnerParty lanparty = new DinnerParty((int)NumberUpDown1.Value, CheckBoxHealth.Checked, CheckBoxDecotations.Checked);

    public Form1()
    {


        InitializeComponent();
        //putting the instantiation here doesn't create the object. 
        DinnerParty lanparty = new DinnerParty((int)NumberUpDown1.Value, CheckBoxHealth.Checked, CheckBoxDecotations.Checked);


        DisplayDinnerPartyCost();
    }

编辑：我接受了Ryan的建议，但现在它说的是我引用的对象 在DisplayDinnerPartyCost（）中，方法为null。以下是更相关的 代码

编辑：这是整个类和表单代码

    //class
    namespace DinnerParty
    {
        public class DinnerParty
        {
            public const int CostOfFoodPerPerson = 25;
            public int NumberOfPeople { get; set; }
            public bool FancyDecorations { get; set; }
            public bool HealthyOption { get; set; }
            public decimal Cost { get
                {
                    decimal totalcost = CalculateDecorations(FancyDecorations);
                totalcost += 
((CalculateCostOfBeveragesPerPerson(HealthyOption) + CostOfFoodPerPerson) * 
NumberOfPeople);

                if (HealthyOption)
                {
                    totalcost *= .95M;
                    return totalcost;
                }
                else
                {
                    return totalcost;
                }


            }


        }



        public DinnerParty(int numberOfPeople, bool healthyOption, bool 
fancyDecorations)
        {
            NumberOfPeople = numberOfPeople;
            HealthyOption = healthyOption;
            FancyDecorations = fancyDecorations;
        }

        private decimal CalculateDecorations(bool fancy)
        {
            decimal CostDeco;
            if (FancyDecorations)
            {
                 CostDeco = (NumberOfPeople * 15.00M) + 50M;
                return CostDeco;
            }
            else
            {
                 CostDeco = (NumberOfPeople * 7.50M) + 30M;
                return CostDeco;
            }
        }

        private decimal CalculateCostOfBeveragesPerPerson(bool Health)
        {
            if (HealthyOption)
            {
                decimal CostOfBeverages = 5.00M;
                return CostOfBeverages;

            }
            else
            {
                decimal CostOfBeverages = 20.00M;
                return CostOfBeverages;
            }
        }



    }
}
//Form code
{
    public partial class Form1 : Form
    {



        DinnerParty lanparty = null; 




        public Form1()
        {           
            InitializeComponent();
            DisplayDinnerPartyCost();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
             lanparty = new DinnerParty((int)NumberUpDown1.Value, 
CheckBoxHealth.Checked, CheckBoxDecotations.Checked);

            DisplayDinnerPartyCost();
        }


        public void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            lanparty.NumberOfPeople = (int) NumberUpDown1.Value;
            DisplayDinnerPartyCost();    
        }

        public void CheckBoxDecotations_CheckedChanged(object sender, 
EventArgs e)
        {
            lanparty.FancyDecorations = CheckBoxDecotations.Checked;
            DisplayDinnerPartyCost();
        }

        public void CheckBoxHealth_CheckedChanged(object sender, EventArgs 
e)
        {
            lanparty.HealthyOption = CheckBoxHealth.Checked;
            DisplayDinnerPartyCost();
        }

        public void DisplayDinnerPartyCost()
        {
           decimal cost = lanparty.Cost;
           labelRetrunCost.Text = cost.ToString("c");
        }


    }
}

---

您必须等待直到执行表单加载

namespace DinnerParty
{
    public partial class Form1 : Form
    {
        DinnerParty lanparty = null;

        public Form1()
        {
            InitializeComponent();
        }

        // Make sure to add event handler for Load
        private void Form1_Load(object sender, EventArgs e)
        {
            lanparty = new DinnerParty((int)NumberUpDown1.Value,
                                       CheckBoxHealth.Checked,
                                       CheckBoxDecotations.Checked);
            DisplayDinnerPartyCost();
        }

        // Make sure that any code that references lanparty does not execute while it is null
        public void numericUpDown1_ValueChanged(object sender, EventArgs e)
        {
            if (lanparty != null)
            {
                lanparty.NumberOfPeople = (int) NumberUpDown1.Value;
                DisplayDinnerPartyCost();    
            }
        }

        public void CheckBoxDecotations_CheckedChanged(object sender, EventArgs e)
        {
            if (lanparty != null)
            {
                lanparty.FancyDecorations = CheckBoxDecotations.Checked;
                DisplayDinnerPartyCost();
            }
        }

        public void CheckBoxHealth_CheckedChanged(object sender, EventArgs e)
        {
            if (lanparty != null)
            {
                lanparty.HealthyOption = CheckBoxHealth.Checked;
                DisplayDinnerPartyCost();
            }
        }

        // You may need a functions like this, depending on how your code works
        private void GetLanPartyConfiguration()
        {
            if (lanparty != null)
            {
                lanparty.NumberOfPeople = (int) NumberUpDown1.Value;
                lanparty.HealthyOption = CheckBoxHealth.Checked;
                lanparty.FancyDecorations = CheckBoxDecotations.Checked;
            }
        }

        private void SetLanPartyControls()
        {
            if (lanparty != null)
            {
                NumberUpDown1.Value = lanparty.NumberOfPeople;
                CheckBoxHealth.Checked = lanparty.HealthyOption;
                CheckBoxDecotations.Checked = lanparty.FancyDecorations;
            }
        }

        public void DisplayDinnerPartyCost()
        {
            if (lanparty != null)
            {
                decimal cost = lanparty.Cost;
                labelRetrunCost.Text = cost.ToString("c");
            }
        }
    }
}

---

您的完整代码表明您具有以下功能：

public Form1()
{
    InitializeComponent();
    DisplayDinnerPartyCost();
}

该代码在

Form\u Load

之前执行，因此

lanparty

在该阶段仍然是

null

如果您这样编写代码：

public Form1()
{
    InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
    lanparty = new DinnerParty((int)NumberUpDown1.Value, CheckBoxHealth.Checked, CheckBoxDecotations.Checked);
    DisplayDinnerPartyCost();
}

…应该很好用

---

我对你的代码做了一些重构。当费用发生变化时，你应该让

晚餐派对

举办活动。然后，您仅在该事件触发时更新UI。这确保必须填充

lanparty

以下是晚餐派对的

：

public class DinnerParty
{
    private int _numberOfPeople;
    private bool _fancyDecorations;
    private bool _healthyOption;

    public int CostOfFoodPerPerson { get; } = 25;

    public int NumberOfPeople
    {
        get => _numberOfPeople;
        set
        {
            _numberOfPeople = value;
            this.CostUpdated?.Invoke(this, new EventArgs());
        }
    }

    public bool FancyDecorations
    {
        get => _fancyDecorations;
        set
        {
            _fancyDecorations = value;
            this.CostUpdated?.Invoke(this, new EventArgs());
        }
    }

    public bool HealthyOption
    {
        get => _healthyOption;
        set
        {
            _healthyOption = value;
            this.CostUpdated?.Invoke(this, new EventArgs());
        }
    }

    public event EventHandler CostUpdated;

    public DinnerParty(int numberOfPeople, bool healthyOption, bool fancyDecorations)
    {
        this._numberOfPeople = numberOfPeople;
        this._healthyOption = healthyOption;
        this._fancyDecorations = fancyDecorations;
    }

    public decimal Cost
    {
        get
        {
            decimal decorations = CalculateDecorations(_fancyDecorations);
            decimal costOfBeveragesPerPerson = CalculateCostOfBeveragesPerPerson(_healthyOption);
            decimal costPerPerson = costOfBeveragesPerPerson + this.CostOfFoodPerPerson;
            decimal totalcost = costPerPerson * _numberOfPeople + decorations;

            if (_healthyOption)
            {
                totalcost *= .95M;
            }

            return totalcost;
        }
    }

    private decimal CalculateDecorations(bool fancy)
    {
        decimal per = _fancyDecorations ? 15m : 7.5m;
        decimal flat = _fancyDecorations ? 50m : 30m;
        return _numberOfPeople * per + flat;
    }

    private decimal CalculateCostOfBeveragesPerPerson(bool Health)
        => _healthyOption ? 5m : 20m;
}

这是您的
表格1
：

public partial class Form1 : Form
{
    DinnerParty lanparty = null;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        lanparty = new DinnerParty((int)NumberUpDown1.Value, CheckBoxHealth.Checked, CheckBoxDecotations.Checked);
        lanparty.CostUpdated += lanparty_CostUpdated;
        DisplayDinnerPartyCost();
    }

    private void lanparty_CostUpdated(object sender, EventArgs e)
    {
        DisplayDinnerPartyCost();
    }

    private void numericUpDown1_ValueChanged(object sender, EventArgs e)
    {
        lanparty.NumberOfPeople = (int)NumberUpDown1.Value;
    }

    private void CheckBoxDecotations_CheckedChanged(object sender, EventArgs e)
    {
        lanparty.FancyDecorations = CheckBoxDecotations.Checked;
    }

    private void CheckBoxHealth_CheckedChanged(object sender, EventArgs e)
    {
        lanparty.HealthyOption = CheckBoxHealth.Checked;
    }

    public void DisplayDinnerPartyCost()
    {
        decimal cost = lanparty.Cost;
        labelRetrunCost.Text = cost.ToString("c");
    }
}

只是一个小小的旁注：当有人选择健康的选择时，装饰的成本也会打折扣，这似乎很奇怪。也许有什么需要重新思考？
出于某种原因，它仍然会抛出一个错误，表示lanparty为null。这是令人困惑的，因为构造函数应该在窗体上创建一个新对象load@Officer_Narc-如果你需要比Ryan给你的更多的细节，你真的需要发表一篇文章。在这一点上，Ryan看起来是正确的，但是您没有向我们展示的代码中发生了一些事情，因此如果没有进一步的信息，就无法提供帮助。@Officer\u Narc很可能是您在初始化lanparty

之前试图执行代码。您需要等待执行代码，直到

lanparty

不为null，或者使用类似以下内容保护访问lanparty的函数：

if（lanparty==null）{return；}

您需要共享

displaydennerpartycost

方法的代码。还要分享哪行代码出错？@Officer\u Narc-这不是一个错误。我需要能够复制、粘贴和编译您的代码。@Officer\u Narc-我们需要看到需要最少编译工作量的完整类。您可以这样做吗？您正在表单加载事件中初始化对象，同时在构造函数的方法调用中使用对象（构造函数代码将在表单加载之前调用，因此您的新错误需要从

DisplayDinnerPartyCost（）；

中删除

Form1（）

public partial class Form1 : Form
{
    DinnerParty lanparty = null;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        lanparty = new DinnerParty((int)NumberUpDown1.Value, CheckBoxHealth.Checked, CheckBoxDecotations.Checked);
        lanparty.CostUpdated += lanparty_CostUpdated;
        DisplayDinnerPartyCost();
    }

    private void lanparty_CostUpdated(object sender, EventArgs e)
    {
        DisplayDinnerPartyCost();
    }

    private void numericUpDown1_ValueChanged(object sender, EventArgs e)
    {
        lanparty.NumberOfPeople = (int)NumberUpDown1.Value;
    }

    private void CheckBoxDecotations_CheckedChanged(object sender, EventArgs e)
    {
        lanparty.FancyDecorations = CheckBoxDecotations.Checked;
    }

    private void CheckBoxHealth_CheckedChanged(object sender, EventArgs e)
    {
        lanparty.HealthyOption = CheckBoxHealth.Checked;
    }

    public void DisplayDinnerPartyCost()
    {
        decimal cost = lanparty.Cost;
        labelRetrunCost.Text = cost.ToString("c");
    }
}