我是编程和C＃的新手，我正在尝试制作一个小型电子投票系统，当选民投票选出过多的候选人时，如何使投票无效。例如：用户在议员职位上投票选出了7名候选人，而不是6名投票人，我怎样才能使他的投票无效或者不让他提交投票，直到他投票为止。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApplication4
{
public partial class Frm_voteview : Form
{
string userid;
public Frm_voteview()
{
InitializeComponent();
SqlConnection con = new SqlConnection(Properties.Settings.Default.VotingSystemv2ConnectionString);
con.Open();
}
public Frm_voteview(string userid)
{
InitializeComponent();
SqlConnection con = new SqlConnection(Properties.Settings.Default.VotingSystemv2ConnectionString);
con.Open();
this.userid = userid;
}
SqlConnection con = new SqlConnection(Properties.Settings.Default.VotingSystemv2ConnectionString);
private void button3_Click(object sender, EventArgs e)
{
}
private void label3_Click(object sender, EventArgs e)
{
}
private void label5_Click(object sender, EventArgs e)
{
}
private void button7_Click(object sender, EventArgs e)
{
new Frm_Login().Show();
this.Hide();
}
private void button8_Click(object sender, FormClosingEventArgs e)
{
}
private void groupBox1_Enter(object sender, EventArgs e)
{
}
private void Frm_voteview_FormClosing(object sender, FormClosingEventArgs e)
{
}
private void Frm_voteview_Click(object sender, EventArgs e)
{
}
private void btn_submit_Click(object sender, EventArgs e)
{
con.Open();
if (MessageBox.Show("Confirm and View your Votes?", "Close Application", MessageBoxButtons.YesNo) == DialogResult.Yes)
{
MessageBox.Show("Voting Successful", "Application Closed!", MessageBoxButtons.OK);
using (SqlCommand command = new SqlCommand("UPDATE candidate SET cTally = cTally + 1 where cName like @cname or cName like @vName", con))
{
command.Parameters.AddWithValue("@cname", cb_president.Text);
command.Parameters.AddWithValue("@vName", cb_vpresident.Text);
command.ExecuteNonQuery();
}
foreach (object item in lb_councilor.SelectedItems)
{
using (SqlCommand command = new SqlCommand("UPDATE candidate SET cTally = cTally + 1 where cName like @coname", con))
{
command.Parameters.AddWithValue("@coname", (item as DataRowView)["cName"].ToString());
Console.WriteLine((item as DataRowView)["cName"].ToString());
command.ExecuteNonQuery();
}
using (SqlCommand command = new SqlCommand("UPDATE voters SET isVoted = 1 where userName like @uname", con))
{
command.Parameters.AddWithValue("@uname", userid );
command.ExecuteNonQuery();
}
}
this.Close();
new Form4().Show();
this.Hide();
}
else
{
this.Activate();
}
}
private void Frm_voteview_Load(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(Properties.Settings.Default.VotingSystemv2ConnectionString);
con.Open();
// TODO: This line of code loads data into the 'votingSystemv2DataSet7.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter2.Fill(this.votingSystemv2DataSet7.candidate);
// TODO: This line of code loads data into the 'votingSystemv2DataSet5.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter1.Fill(this.votingSystemv2DataSet5.candidate);
// TODO: This line of code loads data into the 'votingSystemv2DataSet4.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter.Fill(this.votingSystemv2DataSet4.candidate);
}
private void dgv_councilor_CellMouseDown(object sender, DataGridViewCellMouseEventArgs e)
{
}
private void dgv_councilor_RowHeaderMouseClick(object sender, DataGridViewCellMouseEventArgs e)
{
}
private void Frm_voteview_FormClosed(object sender, FormClosedEventArgs e)
{
SqlConnection con = new SqlConnection(Properties.Settings.Default.VotingSystemv2ConnectionString);
// TODO: This line of code loads data into the 'votingSystemv2DataSet7.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter2.Fill(this.votingSystemv2DataSet7.candidate);
// TODO: This line of code loads data into the 'votingSystemv2DataSet5.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter1.Fill(this.votingSystemv2DataSet5.candidate);
// TODO: This line of code loads data into the 'votingSystemv2DataSet4.candidate' table. You can move, or remove it, as needed.
this.candidateTableAdapter.Fill(this.votingSystemv2DataSet4.candidate);
con.Close();
}
private void button1_Click(object sender, EventArgs e)
{
new Form9().Show();
}
private void cb_president_SelectedIndexChanged(object sender, EventArgs e)
{
}
private void lb_councilor_SelectedIndexChanged(object sender, EventArgs e)
{
}
}
}
答案 0 :(得分：1)
欢迎来到C＃。
好的，很少。首先，你的问题的答案？看看你的代码行：
foreach (object item in lb_councilor.SelectedItems)
......这样做是循环选择了一系列项目。好吧，尝试输入lb_councilor.SelectedItems - 希望你在VisualStudio中的intellisense会告诉你它是什么（可能是IEnumerable之类的东西。）
[这是VS的一个很好的技巧 - 输入变量/对象/什么，看看intellisense提出了什么。]
好吧，好消息是，像IEnumerable这样的东西有一个Count方法。所以你的问题可能很简单：if (lb_councilor.SelectedItems.Count != 6)
{
// uh oh. Better stop them.
好的，现在已经不在了，还有一些额外的东西：
确保为每个找到代码的对象命名。 candidateTableAdapter1，votingSystemv2DataSet5，label5，button1，Form9 - 如果你提交引用一堆默认命名项的代码，你将会让其他开发人员的生活成为一场噩梦。
不要使用＆＃39; object＆＃39;除非你能帮助它，否则在环绕一个foreach时。这是您的代码正在做什么
foreach (object something in somegroup)
{
use(something as DataRowView);
}
...也就是说，你正在施展某些东西＆＃39;作为一个对象......但之后你就将它用作DataRowView。你也可以这样做：
foreach (DataRowView something in somegroup)
或者至少做这样的事情：
foreach (object something in somegroup)
{
if (something is DataGridView)
{
// your code is safe from an unexpected data type now
use(something as DataGridView);