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對不起再次提出這個問題，但我真的不知道如何調試。
調試器在這一行給我nullreferenceexception： if（listBox1.SelectedItem.ToString（）==「Chicken $ 15」） 我認爲它給我nullreferenceexception的原因是因爲listbox1爲空，所以我想我必須初始化它。但是如何？我不知道如何初始化列表框。如何在列表框中修復nullreferenceexception？
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 lab6
{
public partial class Form1 : Form
{
double total = 0;
int x = 0;
string ord = "";
public Form1()
{
InitializeComponent();
}
private void toolStripMenuItem1_Click(object sender, EventArgs e)
{
}
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void menuStrip1_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
{
}
private void editToolStripMenuItem_Click(object sender, EventArgs e)
{
}
private void placeToolStripMenuItem_Click(object sender, EventArgs e)
{
checkBox1.Checked = false;
radioButton1.Checked = false;
radioButton2.Checked = false;
radioButton3.Checked = false;
radioButton4.Checked = false;
switch (checkBox1.Checked)
{
case true:
total += 1;
ord += "Water\n";
break;
}
if (comboBox1.Text == "Extra Meat")
{
total += 1;
ord += ord + "Extra Meat\n";
}
if (comboBox1.Text == "Extra Rice")
{
total += 1;
ord += "Extra Rice\n";
}
if (comboBox1.Text == "Extra Veggies")
{
total += 1;
ord += "Extra Veggies\n";
}
if (listBox1.SelectedItem.ToString() == "Chicken $15")
{
total += 15;
ord += " Chicken\n";
}
else { }
if (listBox1.SelectedItem.ToString() == "Pizza $8") //< my pathetic attempt to figure it out with intelisense
{
total += 8;
ord += "Pizza\n";
}
else
{
}
if (listBox1.SelectedItem.ToString() == "Spaghetti $12")//< my pathetic attempt to figure it out with intelisense
{
total += 12;
ord += " Spaghetti\n";
}
else { }
if (listBox1.SelectedItem.ToString() == "Fries $8")
{
total += 8;
ord += " Fries\n";
}
else { }
if (listBox1.SelectedItem.ToString() == "Burger $10")
{
total += 10;
ord += " Burger\n";
}
else { }
//radiobutton
if (radioButton1.Checked)
{
total+=5;
ord += "Pineapple Juice\n";
}
if (radioButton2.Checked)
{
total+=6;
ord += "Mango Juice\n";
}
if (radioButton3.Checked)
{
total+=7;
ord += "Apple Juice\n";
}
if (radioButton4.Checked)
{
total+=8;
ord += "Orange Juice\n";
}
MessageBox.Show("Order Done");
listBox1.SelectedItems.Clear();
}
private void clearToolStripMenuItem_Click(object sender, EventArgs e)
{
ord = "";
total = 0;
}
private void radioButton1_CheckedChanged(object sender, EventArgs e)
{
}
private void label3_Click(object sender, EventArgs e)
{
}
private void radioButton2_CheckedChanged(object sender, EventArgs e)
{
}
private void radioButton4_CheckedChanged(object sender, EventArgs e)
{
}
private void radioButton3_CheckedChanged(object sender, EventArgs e)
{
}
private void checkBox1_CheckedChanged(object sender, EventArgs e)
{
}
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
}
private void label4_Click(object sender, EventArgs e)
{
}
private void displayToolStripMenuItem_Click(object sender, EventArgs e)
{
MessageBox.Show("Order: " + ord+"\nTotal: "+total);
}
private void exitToolStripMenuItem_Click(object sender, EventArgs e)
{
this.Close();
}
}
}
'NullReferenceException'是初級程序員一個常見的情況。所提供的鏈接應該有助於你理解問題。然後使用調試器來查找什麼/哪裏/何時有一個變量是'null'。 – 2014-09-13 11:15:00
你確認'listBox1'是'null'嗎？或者是'listBox1.SelectedItem'什麼是'null'？您可以使用調試器對代碼進行調試，在代碼行中放置斷點，並在運行時檢查調試器中的值。 – David 2014-09-13 11:15:24