抛出的NullReferenceException
抛出的NullReferenceException
提问于 2013-12-09 17:22:11
我是C#.NET的初学者，我们的任务是创建一个在线银行系统，其中交易和登录数据存储在一个类的数组中。虽然我慢慢地掌握了整个类数组的概念，但我似乎无法将登录数据保存到类的数组中。下面是我的程序：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using BankTransaction;
namespace LabExam1
{
public partial class Registration : Form
{
Transactions trans = new Transactions();
int number = 10000;
int x = 0;
const int size = 100;
Transactions[] loginData = new Transactions[size];
public void saveLoginData()
{
loginData[x].Username = trans.createUserName(txtFname.Text, txtLname.Text, txtMi.Text);
loginData[x].Password = txtPass.Text;
x++;
}
public Registration()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
cboType.SelectedIndex = 0;
}
private void btnRegister_Click(object sender, EventArgs e)
{
if (txtFname.Text == "" || txtLname.Text == ""|| txtMi.Text == "" || txtPass.Text == "")
{
MessageBox.Show("Please fill up all required fields!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Warning);
}
else
{
if (cboType.SelectedIndex == 0)
{
number++;
loginData[x] = new Transactions();
saveLoginData();
MessageBox.Show("Generated Username: " + loginData[x].Username + number + "\n" + "Please do not share this Information to anyone!");
this.Hide();
Transaction tr = new Transaction();
tr.ShowDialog();
}
if (cboType.SelectedIndex == 1)
{
if (nudDeposit.Value < 2500.00m)
{
MessageBox.Show("The initial deposit for your account type is insufficient", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Warning);
}
else
{
number++;
loginData[x] = new Transactions();
saveLoginData();
MessageBox.Show("Generated Username: " + loginData[x].Username + number + "\n" + "Please do not share this Information to anyone!");
this.Hide();
Transaction tr = new Transaction();
tr.ShowDialog();
}
}
if (cboType.SelectedIndex == 2)
{
if (nudDeposit.Value < 3000.00m)
{
MessageBox.Show("The initial deposit for your account type is insufficient", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Warning);
}
else
{
number++;
loginData[x] = new Transactions();
saveLoginData();
MessageBox.Show("Generated Username: " + loginData[x].Username + number + "\n" + "Please do not share this Information to anyone!");
this.Hide();
Transaction tr = new Transaction();
tr.ShowDialog();
}
}
}
}
private void btnExit_Click(object sender, EventArgs e)
{
Application.Exit();
}
}
}我在这部分得到了一个错误，它抛出了nullReferenceException
MessageBox.Show("Generated Username: " + loginData[x].Username + number + "\n" + "Please do not share this Information to anyone!");
下面是我的类定义：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace BankTransaction
{
public class Transactions
{
String username, password;
#region forArrayOfClassLogin
public String Password
{
get { return password; }
set { password = value; }
}
public String Username
{
get { return username; }
set { username = value; }
}
#endregion
public String createUserName(String fname, String lname, String mi)
{
String firstString = fname[0].ToString();
String secondString = mi[0].ToString();
String thirdString = lname[0].ToString();
String uname = firstString + secondString + thirdString;
return uname;
}
public void setBalance(String type, decimal initialBalance)
{
}
public String getUserName()
{
return username;
}
public String setPassword(String pass)
{
return password = pass;
}
public String getPassword()
{
return password;
}
}
}任何帮助都将不胜感激。提前谢谢。
回答 6
Stack Overflow用户
发布于 2013-12-09 17:28:35
您需要使用loginData[x -1]，因为您已经在saveLoginData()中增加了x的值
MessageBox.Show("Generated Username: " + loginData[x -1].Username + number + "\n" + "Please do not share this Information to anyone!");Stack Overflow用户
发布于 2013-12-09 17:28:58
这个问题似乎出现在函数saveLoginData()的"x++;“行中。
使用X=0将X声明为成员级变量。
当你在"saveLoginData()“函数中增加x的值时，它变成了X=1，然后在尝试访问父函数中的数组时，X的值现在是1，但是你的数组没有为该索引存储任何值，这导致了异常。
Stack Overflow用户
发布于 2013-12-09 17:25:58
String firstString = fname[0].ToString();
String secondString = mi[0].ToString();
String thirdString = lname[0].ToString();安装上面的行尝试做
String firstString = fname;
String secondString = mi;
String thirdString = lname;有关更多详细信息，请参阅以下链接。http://msdn.microsoft.com/en-us/library/ms228362.aspx
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/20467090
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