C#为什么我的变量不能在表单之间正确地传递
本文关键字:之间 正确地 表单 为什么 我的 变量 不能 | 更新日期: 2023-09-27 17:50:56
我有几个表单,其中一些表单依赖于每个表单之间的信息。在这种情况下,Form 2
(AKA testSelect(中所选选项的所选索引是决定Form 3
(AKA testPresent(中会发生什么的关键。这被放入一个称为index
的整数中。在关闭form 2
时,index
的值肯定是列表框的selectedindex
的值
然而,在form 3
中打开并应用它时,它一直重置为0,我不知道为什么。以下是在form 2
中使用/确定index
的代码以及在form 3
中调用它的代码。此外,它是在form 2
开始时定义的公共int;
private void lstExams_SelectedIndexChanged(object sender, EventArgs e)
{
try
{
//Create a connection object to the DB via string location
con = new OleDbConnection(connectionString);
//Open the connection to the DB
con.Open();
String sql = "SELECT typeID, description FROM TestConfiguration WHERE examID = " +(lstExams.SelectedIndex +1);
OleDbDataAdapter da = new OleDbDataAdapter(sql, con);
//DataSet ds = new DataSet();
DataTable testConfig = new DataTable();
//Set the SQL command text
da.Fill(testConfig);
lstTestType.DisplayMember = "description";
lstTestType.ValueMember = "typeID";
lstTestType.DataSource = testConfig;
index = lstExams.SelectedIndex + 1;
MessageBox.Show("INDEX = " + index);
}
catch (Exception err)
{
//If cannot connect to DB, display the error;
MessageBox.Show("A Database error has occurred: " + Environment.NewLine + err.Message);
}
}
private void btnStart_Click(object sender, EventArgs e)
{
//var testPresent = new testPresent(this);
testPresent testForm = new testPresent();
testForm.Show();
//testForm.difficulty = lstTestType.ValueMember;
this.Close();
MessageBox.Show("INDEX IS " + index);
testForm.eID = (index);
}
对于form 3
public partial class testPresent : Form
{
public int eID = 0;
public String difficulty;
testSelect select = new testSelect();
//Get the connection path to the DB from the static class
String connectionString = staticConnectionString.connectionString;
//Declare connection object
OleDbConnection con;
public testPresent()
{
InitializeComponent();
}
public void testPresent_Load(object sender, EventArgs e)
{
try
{
int qID;
Random random = new Random();
int examID;
bool valid = false;
String theQuestion;
eID += select.index;
//Create a connection object to the DB via string location
con = new OleDbConnection(connectionString);
//Open the connection to the DB
con.Open();
MessageBox.Show("eID = " + select.index);
if (eID == 1)
{
...
}
if (eID == 2)
{
...
}
if (eID == 3)
{
...
}
}
catch (Exception err)
{
//If cannot connect to DB, display the error;
MessageBox.Show("A Database error has occurred: " + Environment.NewLine + err.Message);
}
}
哦,是的,这也使用Microsoft Access数据库来填充列表框。
您设置值:
testForm.eID = (index);
但是您在之后这样做表单已经加载,因此testPresent_Load
已经使用了其默认值:
testPresent testForm = new testPresent();
testForm.Show(); // this is where it uses the value
// ...
testForm.eID = (index); // this is where you set it
如果testPresent
表单完全需要该值,并且它需要立即使用该值,请尝试在构造函数中包含该值:
public testPresent(int eid)
{
InitializeComponent();
eID = eid;
}
然后,当你创建一个表单实例时,你必须传递这个值:
testPresent testForm = new testPresent(index);
testForm.Show();
在这一点上,不需要从外部设置值,所以它应该是私有的。(无论如何,数据成员在对象上都应该是私有的。(:
private int eID;