Question

大家好，当我尝试执行项目时，当我试图存储对象时出现此错误。正如您所看到的，这是拾取形式，允许用户将值存储在不同的类中。这个值将有3个不同的类存储在...你看到我仍然是c＃thing的新手。我有客户类，将存储客户的详细信息，皮卡类别与皮卡的详细信息和交付相同。和其他类访问只会在时间到来时存储。我不知道这是不是问题..如果你想看到更多代码，请告诉我..谢谢

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


namespace coursework2
{

    public partial class PickupForm : Form
    {
        private MainForm mainform;
        private Pickup thePickup;
        private Delivery theDelivery;
        private Visit theVisit;


      public Pickup pickup
        {
            get { return thePickup;}
            set { thePickup = value;}
        }
      public Delivery delivery
      {
          get { return theDelivery; }
          set { theDelivery = value; }
      }

      public Visit visit
      {
          get { return theVisit; }
          set { theVisit = value; }

      }

        public PickupForm()
        {
            InitializeComponent();
        }

        /*public MainForm ParentForm
        {
            get { return mainform; }
            set { mainform = value; }
        }*/

        private void PickupForm_Load(object sender, EventArgs e)
        {
           if (thePickup != null)
            {
                textCname.Text = thePickup.PickupName;
                textAddress.Text = thePickup.PickupAddress;
                textDate.Text = theVisit.DateTime.ToString();
                textDname.Text = theDelivery.DeliveryName;
                textDaddress.Text = theDelivery.DeliveryAddress;
            }
        }

        private void btnReturn_Click(object sender, EventArgs e)
        {

            this.Close();
            /*mainform.Show();*/
        }


        private void btnClear_Click(object sender, EventArgs e)
        {
            textCname.Clear();
            textAddress.Clear();
            textDate.Clear();
            textDname.Clear();
            textDaddress.Clear();
        }

        private void btnPickup_Click(object sender, EventArgs e)
        {
            thePickup.PickupName = textCname.Text; //error occurs from this line
            thePickup.PickupName = textAddress.Text;
            theVisit.DateTime = DateTime.Parse(textDate.Text);
            theDelivery.DeliveryName = textDname.Text;
            theDelivery.DeliveryAddress = textDaddress.Text;



            this.Close();
        }




        private void textDate_TextChanged(object sender, EventArgs e)
        {

        }

        private void textCname_TextChanged(object sender, EventArgs e)
        {

        }
    }
}

Answer 1

您正在访问thePickup的属性，但在任何时候都没有为变量分配对象。所以thePickup仍然是null，这就是你得到NullReferenceException的原因。

在某些时候，您需要实例化一个Pickup对象并将其分配给thePickup，如下所示：

thePickup = new Pickup();

您应该在构造函数或PickupForm_Load事件处理程序中执行此操作。

theVisit和theDelivery同样如此。

Answer 2

private void PickupForm_Load(object sender, EventArgs e)
{
    if(thePickup == null)
    {
        thePickup = new Pickup();
    }

    if(theDelivery == null)
    {
        theDelivery = new Delivery();
    }

    if(theVisit == null)
    {
        theVisit =  new Visit();
    }

    textCname.Text = thePickup.PickupName;
    textAddress.Text = thePickup.PickupAddress;
    textDate.Text = theVisit.DateTime.ToString();
    textDname.Text = theDelivery.DeliveryName;
    textDaddress.Text = theDelivery.DeliveryAddress;   
}

您需要初始化各自的属性

错误System.NullReferenceException

2 个答案: