public partial class _Default : System.Web.UI.Page
{ protected void Page_Load(object sender, EventArgs e)
{
string conStr = ConfigurationManager.ConnectionStrings["mysqlconnection"].ConnectionString;
SqlConnection connection = new SqlConnection(conStr);
connection.Open();
string selectionStr = "SELECT * FROM Shippers";
SqlCommand command = new SqlCommand();
command.Connection = connection;
command.CommandText = selectionStr;
SqlDataReader dataReader = command.ExecuteReader(); while (dataReader.Read())
{
ListBox1.Items.Add(new ListItem(
dataReader[0] + " -- " + dataReader[1] + " -- " + dataReader[2],dataReader[0].ToString()));
}
dataReader.Close(); selectionStr = "SELECT * FROM Products";
command.CommandText = selectionStr;
dataReader = command.ExecuteReader(); ListBox2.DataSource = dataReader;
ListBox2.DataTextField = "ProductName";
ListBox2.DataValueField = "ProductID";
ListBox2.DataBind();
}
protected void Button1_Click(object sender, EventArgs e)
{ TextBox1.Text = ListBox2.SelectedItem.Text;
}为什么 TextBox1.Text = ListBox2.SelectedItem.Text 这行代码在执行时出错?!
Object reference not set to an instance of an object.
谢谢解答!
{ protected void Page_Load(object sender, EventArgs e)
{
string conStr = ConfigurationManager.ConnectionStrings["mysqlconnection"].ConnectionString;
SqlConnection connection = new SqlConnection(conStr);
connection.Open();
string selectionStr = "SELECT * FROM Shippers";
SqlCommand command = new SqlCommand();
command.Connection = connection;
command.CommandText = selectionStr;
SqlDataReader dataReader = command.ExecuteReader(); while (dataReader.Read())
{
ListBox1.Items.Add(new ListItem(
dataReader[0] + " -- " + dataReader[1] + " -- " + dataReader[2],dataReader[0].ToString()));
}
dataReader.Close(); selectionStr = "SELECT * FROM Products";
command.CommandText = selectionStr;
dataReader = command.ExecuteReader(); ListBox2.DataSource = dataReader;
ListBox2.DataTextField = "ProductName";
ListBox2.DataValueField = "ProductID";
ListBox2.DataBind();
}
protected void Button1_Click(object sender, EventArgs e)
{ TextBox1.Text = ListBox2.SelectedItem.Text;
}为什么 TextBox1.Text = ListBox2.SelectedItem.Text 这行代码在执行时出错?!
Object reference not set to an instance of an object.
谢谢解答!
command.CommandText = selectionStr;
dataReader = command.ExecuteReader(); ListBox2.DataSource = dataReader;
ListBox2.DataTextField = "ProductName";
ListBox2.DataValueField = "ProductID";
ListBox2.DataBind();
没有设置Connection
ListBox2为Null吧
没有实例化
单步跟踪看看
command.CommandText = selectionStr;
dataReader = command.ExecuteReader();
ListBox2.DataSource = dataReader;
ListBox2.DataTextField = "ProductID";
ListBox2.DataValueField = "ProductName";
ListBox2.DataBind();加上connection还是一样问题啊!
加到page_load中看看是否可以赋值。别点button
DotNET3, 看MSDN里的, 人家都是这用就可以, 究竟我的代码哪里与她不同?!
<%@ Page Language="C#" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>
<html>
<script language="C#" runat="server">
ICollection CreateDataSource() {
DataTable dt = new DataTable();
DataRow dr;
dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
dt.Columns.Add(new DataColumn("StringValue", typeof(string)));
dt.Columns.Add(new DataColumn("DateTimeValue", typeof(DateTime)));
dt.Columns.Add(new DataColumn("BoolValue", typeof(bool)));
dt.Columns.Add(new DataColumn("CurrencyValue", typeof(double)));
for (int i = 0; i < 9; i++) {
dr = dt.NewRow();
dr[0] = i;
dr[1] = "Item " + i.ToString();
dr[2] = DateTime.Now;
dr[3] = (i % 2 != 0) ? true : false;
dr[4] = 1.23 * (i+1);
dt.Rows.Add(dr);
}
DataView dv = new DataView(dt);
return dv;
}
void Page_Load(Object sender, EventArgs e) {
if (!IsPostBack) {
RadioButtonList1.DataSource = CreateDataSource();
RadioButtonList1.DataTextField="StringValue";
RadioButtonList1.DataValueField="CurrencyValue";
RadioButtonList1.DataBind();
}
}
void Index_Changed(Object sender, EventArgs e) {
//注意下面的三行代码--------------------------------------------------------------
Label1.Text = "You selected " + RadioButtonList1.SelectedItem.Text +
" with a value of $" + RadioButtonList1.SelectedItem.Value +
"."; }
</script>
<body>
<form runat=server>
<asp:RadioButtonList id="RadioButtonList1"
OnSelectedIndexChanged="Index_Changed"
AutoPostBack="true"
runat="server"/>
<br>
<asp:Label id="Label1" runat="server"/>
</form>
</body>
</html>