Develop Reference

Cannot reuse open DataReader

I am writing a c# windows forms application and i am coming accross the error mentioned above. I think this is happening because i am opening an sql connection and reader object in my main form load object and then doing the same thing again in another click event handler. I am not sure what i need to do in order to change my code / stop this from happening (or if this is even the problem). I have tried turning MARS on in my connection string but this did not fix the problem. Below is my code.
namespace Excel_Importer
{
public partial class Export : Form
{
public Export()
{
InitializeComponent();
}
private void cmbItemLookup_SelectedIndexChanged(object sender, EventArgs e)
{
}
private void Export_Load(object sender, EventArgs e)
{
string connectionString = ConfigurationManager.ConnectionStrings ["dbconnection"].ConnectionString;
using (SqlConnection conn = new SqlConnection(connectionString))
{
conn.Open();
SqlCommand cmd = new SqlCommand("Select * From ExportItem", conn);
SqlDataReader rdr;
rdr = cmd.ExecuteReader();
System.Data.DataTable dt = new System.Data.DataTable();
dt.Columns.Add("ExportItemName", typeof(string));
dt.Load(rdr);
cmbItemLookup.DisplayMember = "ExportItemName";
cmbItemLookup.DataSource = dt;
conn.Close();
}
}
private void btnLoad_Click(object sender, EventArgs e)
{
string connectionString = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;
SqlConnection conn = new SqlConnection(connectionString);
conn.Open();
SqlCommand cmd2 = new SqlCommand("Select * from " + cmbItemLookup.Text, conn);
SqlDataReader rdr2;
rdr2 = cmd2.ExecuteReader();
try
{
SqlDataAdapter ada = new SqlDataAdapter();
ada.SelectCommand = cmd2;
DataTable dt = new DataTable();
ada.Fill(dt);
BindingSource bs = new BindingSource();
bs.DataSource = dt;
dgvExport.DataSource = bs;
ada.Update(dt);
conn.Close();
}
catch (Exception Ex)
{
MessageBox.Show(Ex.Message);
}
}
}
}

You need to close your DataReaders. They implement the IDisposable interface, so the simplest thing is to put them inside a using block:
using (rdr = cmd.ExecuteReader())
{
..
} // .NET always calls Dispose() for you here
Actually, you pretty much have to dispose of everything that implements IDisposable, or problems gonna happen.

As the other answer points out, you must tidy up your clicked event code:
private void btnLoad_Click(object sender, EventArgs e)
{
string connectionString = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;
using (SqlConnection conn = new SqlConnection(connectionString) )
{
conn.Open();
using(SqlCommand cmd2 = new SqlCommand("Select * from " + cmbItemLookup.Text, conn) )
{
using(SqlDataReader rdr2= cmd2.ExecuteReader())
{
try
{
SqlDataAdapter ada = new SqlDataAdapter();
ada.SelectCommand = cmd2;
DataTable dt = new DataTable();
ada.Fill(dt);
BindingSource bs = new BindingSource();
bs.DataSource = dt;
dgvExport.DataSource = bs;
ada.Update(dt);
conn.Close();
}
catch (Exception Ex)
{
MessageBox.Show(Ex.Message);
}
}
}
}
}

Gridview in asp.net C#

I have two dropdownlist, corresponding to the values,gridview should be displayed,,and below is code for it..But i am not getting What's the problem in it!!
protected void ddlstudents_SelectedIndexChanged(object sender, EventArgs e)
{
if (ddlstudents.SelectedIndex > 0)
{
BindData();
}
}
private void BindData()
{
try
{
SQLiteConnection con = new SQLiteConnection("data source=C:\\ITS Database\\its.development.sqlite3");
string strquery = "select topics.name,course_coverages.progress from topics JOIN course_coverages on topics.id=course_coverages.topic_id where course_coverages.student_id=#studentid AND course_coverages.course_id=#courseid";
con.Open();
SQLiteCommand cmd = new SQLiteCommand();
cmd.connection=con;
cmd = con.CreateCommand();
cmd.CommandText = strquery;
cmd.Parameters.AddWithValue("#studentid", ddlstudents.SelectedIndex);
cmd.Parameters.AddWithValue("#courseid", ddlcourse.SelectedValue);
SQLiteDataAdapter ada = new SQLiteDataAdapter(cmd.CommandText, con);
SQLiteCommandBuilder cbl = new SQLiteCommandBuilder(ada);
DataTable dt = new DataTable();
ada.Fill(dt);
GridView1.DataSource = dt;
GridView1.DataBind();
con.Close();
}
catch (SQLiteException)
{
}
}
Any Help Would Be Appreciated!!
Thanks in Advance!!

Learn how to find the problem your self. if the gridview not showing correct data you can debug the application and find where it failed.
you have not given how you bind ddlstudents and ddlcourse , check the values you get for ddlstudents.SelectedIndex and ddlcourse.SelectedValue as you expected or not.
if values are correct, you can run the SQL statement on your database with above values and see the results.
If you really need to find the error, remove the try catch statement from your code,
If you catch the exception, do something with it. otherwise don't.

try this
protected void ddlstudents_SelectedIndexChanged(object sender, EventArgs e)
{
if (ddlstudents.SelectedIndex > 0)
{
BindData();
}
}
private void BindData()
{
try
{
SQLiteConnection con = new SQLiteConnection("data source=C:\\ITS Database\\its.development.sqlite3");
string strquery = "select topics.name,course_coverages.progress from topics JOIN course_coverages on topics.id=course_coverages.topic_id where course_coverages.student_id=#studentid AND course_coverages.course_id=#courseid";
con.Open();
SQLiteCommand cmd = new SQLiteCommand();
cmd.connection=con;
cmd = con.CreateCommand();
cmd.CommandText = strquery;
cmd.Parameters.AddWithValue("#studentid", ddlstudents.SelectedValue);
cmd.Parameters.AddWithValue("#courseid", ddlcourse.SelectedValue);
SQLiteDataAdapter ada = new SQLiteDataAdapter(cmd.CommandText, con);
SQLiteCommandBuilder cbl = new SQLiteCommandBuilder(ada);
DataTable dt = new DataTable();
ada.Fill(dt);
GridView1.DataSource = dt;
GridView1.DataBind();
con.Close();
}
catch (SQLiteException)
{
}
}

after bind data to gridview it will not show on table in grid view

I am creating Windows Application in c#. In that Application i want to join two tables and show it as a single table in grid view. After bind datasource to gridview, grid view will
not shown on form....Here is My code
private void btCheckSupplier_Click_1(object sender, EventArgs e)
{
string checkSupplier = tbProdcutId.Text;
try
{
DataSet checkSupplierDataSet = new DataSet();
DataSet n = dal.SupplierDetail(checkSupplierDataSet);
BindingSource bindingSource = new BindingSource();
bindingSource.DataSource = n.DefaultViewManager;
if (dataGridView2.Rows.Count == 0)
{
dataGridView2.AutoGenerateColumns = true;
dataGridView2.DataSource = bindingSource;
}
}
catch (Exception)
{
throw;
}
}
static string conn = #"Data Source=MyComputer-PC\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=True";
public string CheckSupplier(string checkSupplier)//string checkSupplier
{
try
{
string checkString = "select [Products].ProductID,[Products].ProductName,[Suppliers].SupplierID,[Suppliers].CompanyName,[Suppliers].ContactName,[Suppliers].ContactTitle,[Suppliers].Address,[Suppliers].City,[Suppliers].Region,[Suppliers].PostalCode,[Suppliers].Country,[Suppliers].Phone,[Suppliers].Fax,[Suppliers].HomePage from [Products] Inner Join [Suppliers] On [Products].SupplierID = [Suppliers].SupplierID Where [Products].ProductID ='" + checkSupplier + "'";
SqlCommand sqlcom = new SqlCommand(checkString, connect);
connect.Open();
sqlcom.Connection = connect;
sqlcom.ExecuteNonQuery();
connect.Close();
return checkString;
}
catch (Exception)
{
throw;
}
}
public DataSet SupplierDetail(DataSet supplierDetail)
{
try
{
SqlConnection connect = new SqlConnection(conn);
Class2 checkObj = new Class2();
connect.Open();
SqlCommand sqlCom = connect.CreateCommand();
sqlCom.CommandText =checkObj.CheckSupplier(checkString);here checkString is called From CheckSupplier method.
SqlDataAdapter sqlAd = new SqlDataAdapter();
sqlAd.SelectCommand=sqlCom;
sqlAd.Fill(supplierDetail);
connect.Close();
return supplierDetail;
}
catch (Exception)
{
throw;
}
}

Fill: SelectCommand.Connection property has not been initialized

I am using the below code to access the MS Access Database. But i got a error message Fill: SelectCommand.Connection property has not been initialized.How can i solve this issue.
common.cs
=========
public static bool DBConnectionStatus()
{
try
{
string conString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=|DataDirectory|db_admin.mdb; Jet OLEDB:Database Password=admin";
using (OleDbConnection conn = new OleDbConnection(conString))
{
conn.Open();
return (conn.State == ConnectionState.Open);
}
}
catch (OleDbException)
{
return false;
}
protected void btn_general_Click(object sender, EventArgs e)
{
try
{
bool state = common.DBConnectionStatus();
if (state == true)
{
cmd = new OleDbCommand("select * from tbl_admin");
da = new OleDbDataAdapter(cmd);
DataSet ds = new DataSet();
da.Fill(ds); // Error Here
if (ds.Tables[0].Rows.Count > 0)
{
}
}
}
catch (Exception e1)
{
}
}

I did suggest you to modify your code to something like this:
private DataTable YourData()
{
string conString = #"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=|DataDirectory|db_admin.mdb; Jet OLEDB:Database Password=admin";
DataSet ds = new DataSet();
using (SqlConnection conn = new SqlConnection(conString))
{
try
{
conn.Open();
SqlCommand command = new SqlCommand("select * from tbl_admin", conn);
command.CommandType = CommandType.Text;
SqlDataAdapter adapter = new SqlDataAdapter(command);
adapter.Fill(ds);
if (ds.Tables[0].Rows.Count > 0)
{
// do somethign here
}
}
catch (Exception)
{
/*Handle error*/
}
}
return ds.Tables[0];
}
And then:
protected void btn_general_Click(object sender, EventArgs e)
{
this.YourData(); // you will get the Data here. you can then use it the way you want it
}

You are initializing a Command which you use to construct a DataAdapter, but both without setting the required Connection property:
cmd = new OleDbCommand("select * from tbl_admin"); // <-- no connectuion assigned
da = new OleDbDataAdapter(cmd); // <-- no connectuion assigned
So your exception is pretty self-explanatory.
One final note: using will dispose/close the connection, so the method DBConnectionStatus is pointless. So don't use it, instead use the using in in the first place:
try
{
using(var con = new OleDbConnection(connectionString))
using(var da = new OleDbDataAdapter("elect * from tbl_admin", con))
{
var table = new DataTable();
da.Fill(table); // note that you don't need to open the connection with DataAdapter.Fill
if (table.Rows.Count > 0)
{
// ...
}
}
}
catch (Exception e1)
{
// don't catch an exception if you don't handle it in a useful way(at least loggging)
throw;
}

As per your requirement you can also use SqlDataAdapter instand of ExecuteReader.
public void ReadMyData(string connectionString)
{
string queryString = "SELECT OrderID, CustomerID FROM Orders";
using (OleDbConnection connection = new OleDbConnection(connectionString))
{
OleDbCommand command = new OleDbCommand(queryString, connection);
connection.Open();
OleDbDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Console.WriteLine(reader.GetInt32(0) + ", " + reader.GetString(1));
}
// always call Close when done reading.
reader.Close();
}
}

Refreshing Gridview After Button Click

on my asp.net project, how can i refresh my gridview immediately after clicking my button.
my button has update codes.here is the codes;
protected void Button3_Click(object sender, EventArgs e)
{
string strSQL = "UPDATE [bilgiler3] SET [HAM_FM] = ISNULL(MON,0)+ISNULL(TUE,0)+ISNULL(WED,0)+ISNULL(THU,0)+ISNULL(FRI,0)+ISNULL(SAT,0)+ISNULL(SUN,0) WHERE [DATE] BETWEEN #DATE1 AND #DATE2 AND WORK_TYPE='OUT'";
string connStr = WebConfigurationManager.ConnectionStrings["asgdb01ConnectionString"].ConnectionString;
using (SqlConnection conn = new SqlConnection(connStr))
{
using (SqlCommand comm = new SqlCommand())
{
comm.Connection = conn;
comm.CommandText = strSQL;
comm.CommandType = CommandType.Text;
comm.Parameters.AddWithValue("#DATE1", Convert.ToDateTime(TextBox1.Text));
comm.Parameters.AddWithValue("#DATE2", Convert.ToDateTime(TextBox2.Text));
try
{
conn.Open();
int i = comm.ExecuteNonQuery();
conn.Close();
if (i > 0)
{
Response.Write(" SUCCESS ");
}
else
{
Response.Write(" ERROR ! ");
}
}
catch (SqlException ex)
{
Response.Write(ex.ToString());
}
}
}
}
you maybe gonna say "you need to bind the data of your gridview" but i couldnt understand the method.
can you help me about it ?
thank you very much.

I would do the following:
DataSet ds = new DataSet();
SqlDataAdapter sda = new SqlDataAdapter();
SqlConnection sc = new SqlConnection("you connection string here Security=True");
private void loadData()
{
try
{
ds.Clear();
SqlCommand sCmd= new SqlCommand("Load your database", sc);
sda.SelectCommand = sCmd;
sda.Fill(ds, "sCmd");
datagrid.DataSource = ds.Tables["sCmd"];
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
Application.ExitThread();
}
}
something for c# beginners Youtube

Add this code on your button click
SqlConnection con = new SqlConnection("Connection string from web config");
DataSet ds = new DataSet();
SqlDataAdapter sda = new SqlDataAdapter("select * from EmployeeTable", con);
con.Open();
sda.Fill(ds ,"Data");
gridview1.datasource=ds.tables[0];
gridview1.DataBind();

private SqlConnection con;
private SqlConnectionStringBuilder str;
private void Form8_Load(object sender, EventArgs e)
{
loadData();
}
private void loadData()
{
str = new SqlConnectionStringBuilder();
str.Provider = "";
str.DataSource = #"source.accdb";
con = new SqlConnection(str.ConnectionString);
dataGridView1.DataSource = fillTable("Select* from yourTable");
}
private DataTable fillTable(string sql)
{
DataTable datatable = new DataTable();
using (SqlDataAdapter da = new SqlDataAdapter(sql, con))
{
da.Fill(datatable);
}
return datatable;
}
then If you want to refresh the table you put the loaddata(); in the event button_Click hope this help,

DataBind your control on success.
if (i > 0)
{
yourGridView.DataSource=YourDataSource;
yourGridView.DataBind();
Response.Write(" SUCCESS ");
}