C＃NullReferenceException未处理 - 对象引用未设置为对象的实例 [英] C# NullReferenceException was unhandled - Object reference not set to an instance of an object

问题描述

NullReferenceException未被处理过，我试图在C＃中使用Windows Forms创建一个应用程序， - 对象引用未设置为对象的实例

它指向具有以下代码的行：

  carBootSaleList.AddCarBootSale（newCarBootSale）; 
  

我在表单界面上的方法：

CarBootSaleList carBootSaleList;

  
 
 public void AddCarBootSale（）
 {
 AddNewCarBootSale addForm = new AddNewCarBootSale（）; 
 if（addForm.ShowDialog（）== DialogResult.OK）
 {
 CarBootSale newCarBootSale = addForm.GetCarBootSaleData（）; 
 
 carBootSaleList.AddCarBootSale（newCarBootSale）; 
 
 txtCarBootSale.Clear（）; 
 txtCarBootSale.Text = newCarBootSale.Display（）; 
} 
} 
  

CarBootSaleList类：

  public class CarBootSaleList：IDisplay 
 {
 
 private List< CarBootSale> carbootsales; 
 
 public CarBootSaleList（）
 {
 carbootsales = new List< CarBootSale>（）; 
} 
 
 public bool AddCarBootSale（CarBootSale carbootsale）
 {
 bool success = true; 
 foreach（carBootSale cbs in carbootsales）
 {
 if（cbs.ID == carbootsale.ID）
 {
 success = false; 
} 
} 
 if（success）
 {
 carbootsales.Add（carbootsale）; 
} 
 return success; 
} 
 
 public int GetListSize（）
 {
 return carbootsales.Count（）; 
} 
 
 // public CarBootSale FindCarBootSale（string cbsID）
 // {
 // CarBootSale carbootsale = null; 
 // foreach（carBootSale cbs in carbootsale）
 // {
 // if（cbs.ID == cbsID）
 // {
 // carbootsale = CBS; 
 //} 
 //} 
 // return carbootsale; 
 //} 
 
 public List< CarBootSale> ReturnList（）
 {
 return carbootsales; 
} 
 
 public string Display（）
 {
 string msg =; 
 
 foreach（carBootSale cbs in carbootsales）
 {
 msg + = String.Format（{0} {1}，cbs.ID，cbs.Location，cbs。日期）; 
 msg + = Environment.NewLine; 
} 
 return msg; 
} 
} 
  

CarBootSale类：

  public class CarBootSale：IDisplay 
 {
 
 public string ID {get;组; } 
 public string Date {get;组; } 
 public string Location {get;组; } 
 public double PitchCost {get;组; } 
 public int Capacity {get;组; } 
 public string Charity {get;组; } 
 public string CharityName {get;组; } 
 public string Catering {get;组; 
 
 public CarBootSale（string id，string date，string location，double pitchcost，int capacity，string charity，string charityname，string catering）
 {
 ID = id; 
 Date = date; 
位置=位置; 
 PitchCost = pitchcost; 
容量=容量; 
慈善=慈善; 
 CharityName = charityname; 
餐饮=餐饮; 
} 
 
 public CarBootSale（）{} 
 
 public override string ToString（）
 {
 return String.Format（{0 } {1}，ID，日期，位置）; 
} 
 
 public string Display（）
 {
 string msg; 
 string CR = Environment.NewLine; 
 
 msg = String.Format（ID：{0} {1}，ID，CR）; 
 msg + = String.Format（Date：{0} {1}，Date，CR）; 
 msg + = String.Format（Location：{0} {1}，Location，CR）; 
 msg + = String.Format（Pitch Cost：{0} {1}，PitchCost，CR）; 
 msg + = String.Format（容量：{0} {1}，容量，CR）; 
 msg + = String.Format（Charity：{0} {1}，Charity，CR）; 
 msg + = String.Format（CharityName：{0} {1}，CharityName，CR）; 
 msg + = String.Format（Catering：{0} {1}，Catering，CR）; 
 
 return msg; 
} 
} 
  

解决方案

变量 carBootSaleList 未初始化，因此 null 。

尝试替换

  CarBootSaleList carBootSaleList; 
  

与

  CarBootSaleList carBootSaleList = new CarBootSaleList（）; 
  

I'm trying to create a application using Windows Forms in C#, however I keep getting an error stating:

NullReferenceException was unhandled - Object reference not set to an instance of an object

It's pointing to the line which has this code on:

carBootSaleList.AddCarBootSale(newCarBootSale);

The method I have on the forms interface:

  CarBootSaleList carBootSaleList;

  public void AddCarBootSale()
    {
        AddNewCarBootSale addForm = new AddNewCarBootSale();
        if (addForm.ShowDialog() == DialogResult.OK)
        {
            CarBootSale newCarBootSale = addForm.GetCarBootSaleData();

            carBootSaleList.AddCarBootSale(newCarBootSale);

            txtCarBootSale.Clear();
            txtCarBootSale.Text = newCarBootSale.Display();
        }
    }

The CarBootSaleList class:

public class CarBootSaleList : IDisplay
{

    private List<CarBootSale> carbootsales;

    public CarBootSaleList()
    {
        carbootsales = new List<CarBootSale>();
    }

    public bool AddCarBootSale(CarBootSale carbootsale)
    {
        bool success = true;
        foreach (CarBootSale cbs in carbootsales)
        {
            if (cbs.ID == carbootsale.ID)
            {
                success = false;
            }
        }
        if (success)
        {
            carbootsales.Add(carbootsale);
        }
        return success;
    }

    public int GetListSize()
    {
        return carbootsales.Count();
    }

    //public CarBootSale FindCarBootSale(string cbsID)
    //{
    //    CarBootSale carbootsale = null;
    //    foreach (CarBootSale cbs in carbootsale)
    //    {
    //        if (cbs.ID == cbsID)
    //        {
    //            carbootsale = cbs;
    //        }
    //    }
    //    return carbootsale;
    //}

    public List<CarBootSale> ReturnList()
    {
        return carbootsales;
    }

    public string Display()
    {
        string msg = "";

        foreach (CarBootSale cbs in carbootsales)
        {
            msg += String.Format("{0}  {1}", cbs.ID, cbs.Location, cbs.Date);
            msg += Environment.NewLine;
        }
        return msg;
    }
}

The CarBootSale class:

public class CarBootSale : IDisplay
{

    public string ID { get; set; }
    public string Date { get; set; }
    public string Location { get; set; }
    public double PitchCost { get; set; }
    public int Capacity { get; set; }
    public string Charity { get; set; }
    public string CharityName { get; set; }
    public string Catering { get; set; }

    public CarBootSale(string id, string date, string location, double pitchcost, int capacity, string charity, string charityname, string catering)
    {
        ID = id;
        Date = date;
        Location = location;
        PitchCost = pitchcost;
        Capacity = capacity;
        Charity = charity;
        CharityName = charityname;
        Catering = catering;
    }

    public CarBootSale() { }

    public override string ToString()
    {
        return String.Format("{0}  {1}", ID, Date, Location);
    }

    public string Display()
    {
        string msg;
        string CR = Environment.NewLine;

        msg = String.Format("ID: {0} {1}", ID, CR);
        msg += String.Format(" Date: {0} {1}", Date, CR);
        msg += String.Format(" Location: {0} {1}", Location, CR);
        msg += String.Format(" Pitch Cost: {0} {1}", PitchCost, CR);
        msg += String.Format(" Capacity: {0} {1}", Capacity, CR);
        msg += String.Format(" Charity: {0} {1}", Charity, CR);
        msg += String.Format(" CharityName: {0} {1}", CharityName, CR);
        msg += String.Format(" Catering: {0} {1}", Catering, CR);

        return msg;
    }
}

解决方案

The variable carBootSaleList wasn't initialized, and it is therefore null.

Try replacing

CarBootSaleList carBootSaleList;

with

CarBootSaleList carBootSaleList = new CarBootSaleList();

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