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how to assign values to DataKeyNames in gridview programatically using C#

I have a GridView. I am adding columns in it through c# in GridView gvExemptSub and retrieving data from another GridView gvSubj on button click. I want to assign data row values to DataKeyNames which I am retrieving from another GridView but I don't know how.
<asp:GridView ID="gvExemptSub" runat="server" Width="100%" DataKeyNames="LID,BID">
<Columns>
</Columns>
</asp:GridView>
protected void BtnAddSubj_Click(object sender, EventArgs e)
{
DataTable dt = new DataTable();
dt.TableName = "ExemptSubj";
dt.Columns.Add("QUALIFICATION", typeof(string));
dt.Columns.Add("SUBJECT", typeof(string));
dt.Columns.Add("LEVEL", typeof(string));
dt.Columns.Add("UNIVERSITY", typeof(string));
DataRow dr;
foreach (GridViewRow srow in gvSubj.Rows)
{
if (srow.RowType == DataControlRowType.DataRow)
{
dr = dt.NewRow();
dr[0] = ddlQualification.SelectedItem;
string SUBJECT = srow.Cells[1].Text;
SUBJECT = SUBJECT.Replace("amp;", "");
dr[1] = SUBJECT;
dr[4] = int.Parse(gvSubj.DataKeys[srow.RowIndex]["LEVEL_ID"].ToString());
dr[2] = srow.Cells[2].Text;
dr[3] = ddlUNI.SelectedItem.Text;
dr[5] = ddlUNI.SelectedValue;
dt.Rows.Add(dr);
}
}
ViewState["ExemptSubj"] = dt;
//gvExemptSubj.DataKeyNames = (dr[4], dr[5])
gvExemptSubj.DataSource = dt;
gvExemptSubj.DataBind();
}

You can bind them programmatically with an string array:
GridView1.DataKeyNames = new string[2] { "ColumnA", "ColumnB" };

ASP.NET dropdownlist in GridView keeps clearing up

I have 2 dropdownlists in grid view. The selection of the first one (EqpCatDDL) will determine what values the second one (DescripDDL) will be populated with.
However, everytime I click the Add New Row button, the DescripDDL dropdownlist clears up. I don't know why it does that. The following is the code:
aspx:
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel runat="server">
<ContentTemplate>
<asp:GridView ID="Gridview1" runat="server" ShowFooter="True" AutoGenerateColumns="False"
OnRowDataBound="Gridview1_RowDataBound">
<Columns>
<asp:BoundField DataField="S/N" HeaderText="S/N" />
<asp:TemplateField HeaderText="Item Name">
<ItemTemplate>
<asp:DropDownList ID="EqpCatDDL" runat="server" AutoPostBack="true" OnSelectedIndexChanged="EqpCatDDL_SelectedIndexChanged">
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Description">
<ItemTemplate>
<asp:DropDownList ID="DescripDDL" runat="server" AutoPostBack="true">
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Quantity">
<ItemTemplate>
<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Remarks">
<ItemTemplate>
<asp:TextBox ID="TextBox4" runat="server"></asp:TextBox>
</ItemTemplate>
<FooterStyle HorizontalAlign="Right" />
<FooterTemplate>
<contenttemplate>
<asp:Button ID="ButtonAdd" onclick="ButtonAdd_Click" runat="server" Text="Add New Row" />
</contenttemplate>
</FooterTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</ContentTemplate>
</asp:UpdatePanel>
c#:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
SetInitialRow(); //create a datatable to bind to GridView
}
}
private void SetInitialRow()
{
DataTable dt = new DataTable();
DataRow dr = null;
dt.Columns.Add(new DataColumn("S/N", typeof(string)));
dt.Columns.Add(new DataColumn("Column1", typeof(string)));
dt.Columns.Add(new DataColumn("Column2", typeof(string)));
dt.Columns.Add(new DataColumn("Column3", typeof(string)));
dt.Columns.Add(new DataColumn("Column4", typeof(string)));
dr = dt.NewRow();
dr["S/N"] = 1;
dr["Column1"] = string.Empty;
dr["Column2"] = string.Empty;
dr["Column3"] = string.Empty;
dr["Column4"] = string.Empty;
dt.Rows.Add(dr);
//Store the DataTable in ViewState
ViewState["CurrentTable"] = dt;
Gridview1.DataSource = dt;
Gridview1.DataBind();
}
protected void ButtonAdd_Click(object sender, EventArgs e)
{
AddNewRowToGrid();
GridViewRow row = (GridViewRow)((sender as Button).NamingContainer);
Button btn = row.FindControl("ButtonAdd") as Button;
ScriptManager.GetCurrent(this).RegisterAsyncPostBackControl(btn);
}
private void AddNewRowToGrid()
{
int rowIndex = 0;
if (ViewState["CurrentTable"] != null)
{
DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
DataRow drCurrentRow = null;
if (dtCurrentTable.Rows.Count > 0)
{
//extract the TextBox values
for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
{
//Locate controls in GridView
DropDownList ddl1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("EqpCatDDL");
DropDownList ddl2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[2].FindControl("DescripDDL");
TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("TextBox4");
//Save control values into DataTable
drCurrentRow = dtCurrentTable.NewRow();
drCurrentRow["S/N"] = i + 1;
drCurrentRow["Column1"] = ddl1.SelectedValue.ToString();
drCurrentRow["Column2"] = ddl2.SelectedValue.ToString();
drCurrentRow["Column3"] = box3.Text;
drCurrentRow["Column4"] = box4.Text;
dtCurrentTable.Rows[rowIndex]["Column1"] = ddl1.SelectedValue.ToString();
dtCurrentTable.Rows[rowIndex]["Column2"] = ddl2.SelectedValue.ToString();
dtCurrentTable.Rows[rowIndex]["Column3"] = box3.Text;
dtCurrentTable.Rows[rowIndex]["Column4"] = box4.Text;
rowIndex++;
}
//add new row to DataTable
dtCurrentTable.Rows.Add(drCurrentRow);
//Store the current data to ViewState
ViewState["CurrentTable"] = dtCurrentTable;
//Rebind the Grid with the current data
Gridview1.DataSource = dtCurrentTable;
Gridview1.DataBind();
}
}
else
{
Response.Write("ViewState is null");
}
SetPreviousData(); //Set Previous Data from DataTable to GridView on Postbacks from Add New Row button click
}
private void SetPreviousData()
{
int rowIndex = 0;
if (ViewState["CurrentTable"] != null)
{
DataTable dt = (DataTable)ViewState["CurrentTable"];
if (dt.Rows.Count > 0)
{
for (int i = 0; i < (dt.Rows.Count-1); i++)
{
DropDownList ddl1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("EqpCatDDL");
DropDownList ddl2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[2].FindControl("DescripDDL");
TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("TextBox4");
ddl1.Text = dt.Rows[i]["Column1"].ToString();
ddl2.Text = dt.Rows[i]["Column2"].ToString();
box3.Text = dt.Rows[i]["Column3"].ToString();
box4.Text = dt.Rows[i]["Column4"].ToString();
rowIndex++;
}
}
}
}
//Populate Item Name dropdownlist from EqpCat column in EqpCategory table
protected void Gridview1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
string connString = ConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString;
SqlConnection connection = new SqlConnection(connString);
//Find the DropDownList in the Row
DropDownList EqpCatDDL = (e.Row.FindControl("EqpCatDDL") as DropDownList);
SqlCommand cmd1 = new SqlCommand("SELECT DISTINCT EqpCat FROM EqpCategory", connection);
cmd1.Connection.Open();
SqlDataReader ddlValues1;
ddlValues1 = cmd1.ExecuteReader();
EqpCatDDL.DataSource = ddlValues1;
EqpCatDDL.DataTextField = "EqpCat";
EqpCatDDL.DataValueField = "EqpCat";
EqpCatDDL.DataBind();
cmd1.Connection.Close();
cmd1.Connection.Dispose();
//Add Default Item in the DropDownList
EqpCatDDL.Items.Insert(0, new ListItem("--Select--"));
}
}
//Populate Description dropdownlist based on selected value of Item Name dropdownlist
protected void EqpCatDDL_SelectedIndexChanged(object sender, EventArgs e)
{
string connString = ConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString;
SqlConnection connection = new SqlConnection(connString);
GridViewRow gvr = (GridViewRow)((DropDownList)sender).Parent.Parent;
DropDownList EqpCatDDL = gvr.FindControl("EqpCatDDL") as DropDownList;
DropDownList DescripDDL = gvr.FindControl("DescripDDL") as DropDownList;
string cate = EqpCatDDL.SelectedValue.ToString();
SqlCommand cmd2 = new SqlCommand("SELECT Description FROM EqpCategory WHERE EqpCat = '" + cate + "'", connection);
cmd2.Connection.Open();
SqlDataReader ddlValues2;
ddlValues2 = cmd2.ExecuteReader();
DescripDDL.DataSource = ddlValues2;
DescripDDL.DataTextField = "Description";
DescripDDL.DataValueField = "Description";
DescripDDL.DataBind();
cmd2.Connection.Close();
cmd2.Connection.Dispose();
//Add Default Item in the DropDownList
DescripDDL.Items.Insert(0, new ListItem("--Select--"));
}
I am currently using: Visual Studio 2010 with SSMS 2008

Just modify your SetPreviousData Function
private void SetPreviousData()
{
int rowIndex = 0;
if (ViewState["CurrentTable"] != null)
{
DataTable dt = (DataTable)ViewState["CurrentTable"];
if (dt.Rows.Count > 0)
{
for (int i = 0; i < (dt.Rows.Count - 1); i++)
{
DropDownList ddl1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("EqpCatDDL");
DropDownList ddl2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[2].FindControl("DescripDDL");
TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("TextBox4");
ddl1.SelectedValue = dt.Rows[i]["Column1"].ToString();
string connString = ConfigurationManager.ConnectionStrings["MyDbConn"].ConnectionString;
SqlConnection connection = new SqlConnection(connString);
SqlCommand cmd2 = new SqlCommand(""SELECT Description FROM EqpCategory WHERE EqpCat = '" + Convert.ToInt32(ddl1.SelectedValue) + "'", connection);
cmd2.Connection.Open();
SqlDataReader ddlValues2;
ddlValues2 = cmd2.ExecuteReader();
ddl2.DataTextField = "Description";
ddl2.DataValueField = "Description";
ddl2.DataSource = ddlValues2;
ddl2.DataBind();
cmd2.Connection.Close();
cmd2.Connection.Dispose();
ddl2.SelectedValue = dt.Rows[i]["Column2"].ToString();
box3.Text = dt.Rows[i]["Column3"].ToString();
box4.Text = dt.Rows[i]["Column4"].ToString();
rowIndex++;
}
}
}
}

Use SelectedValue (https://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listcontrol.selectedvalue(v=vs.110).aspx) instead of text to set the selected item.
E.g.:
ddl1.SelectedValue = dt.Rows[i]["Column1"].ToString();
ddl2.SelectedValue = dt.Rows[i]["Column2"].ToString();

how can i remove the gridview column in asp.net c#?

I have a gridview and output generated is
But I want to remove the Column_Name column and want this type of output
Never change SQL query because in this way the query works according to my logic. And I also want to remove &nbsp in every textbox and how can I get all the gridview data by using loop and save in SQL Server database?
ASPX:
<asp:Content ID="Content2" ContentPlaceHolderID="body" Runat="Server">
<form id="form" runat="server">
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="true"
onrowdatabound="GridView1_RowDataBound">
</asp:GridView>
<asp:Button ID="Button1" runat="server" OnClick="load" Text="gridview" />
<asp:Button ID="Button2" runat="server" OnClick="show" Text="Button" />
<asp:Button ID="Button3" runat="server" OnClick="save" Text="Save" />
</form>
</asp:Content>
Codebehind:
SqlConnection cnn = new SqlConnection("Data Source=LIFE_WELL;Initial Catalog=db_compiler;Integrated Security=True");
protected void Page_Load(object sender, EventArgs e)
{
string query = "USE db_compiler SELECT Column_Name FROM tbl_field WHERE Table_Name='deptt'";
SqlCommand cmd = new SqlCommand(query, cnn);
DataTable dt = new DataTable();
SqlDataAdapter adp = new SqlDataAdapter(cmd);
DataTable table = new DataTable();
adp.Fill(dt);
Session["num"] = dt.Rows.Count;
for (int i = 0; i < dt.Rows.Count; i++)
{
DataColumn dc = new DataColumn(dt.Rows[i]["Column_Name"].ToString());
dt.Columns.Add(dc);
}
DataRow r = table.NewRow();
GridView1.DataSource = table;
GridView1.DataBind();
cnn.Close();
cnn.Open();
cmd.ExecuteNonQuery();
cnn.Close();
Session["table"] = dt;
GridView1.DataSource = dt;
GridView1.DataBind();
}
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
for (int i = 0; i < e.Row.Cells.Count; i++)
{
TextBox txt = new TextBox();
txt.Text = e.Row.Cells[i].Text;
e.Row.Cells[i].Text = "";
e.Row.Cells[i].Controls.Add(txt);
}
}
}

Change Your Codebehind code:
protected void Page_Load(object sender, EventArgs e)
{
If(!IsPostBack)
{
string query = "USE db_compiler SELECT Column_Name FROM tbl_field WHERE Table_Name='deptt'";
con.Open();
SqlCommand cmd = new SqlCommand(query, con);
DataTable dt = new DataTable();
SqlDataAdapter adp = new SqlDataAdapter(cmd);
DataTable table = new DataTable();
adp.Fill(dt);
Session["num"] = dt.Rows.Count;
for (int i = 0; i < dt.Rows.Count; i++)
{
DataColumn dc = new DataColumn(dt.Rows[i]["Name"].ToString());
table.Columns.Add(dc); // Make this Column in 2nd DataTable and bind that to Gridview
}
DataRow r = table.NewRow();
Session["table"] = dt;
table.Rows.Add(r); // Add as many row you want to add with for loop
Gridview1.DataSource = table;
Gridview1.DataBind();
}
}
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
for (int i = 0; i < e.Row.Cells.Count; i++)
{
TextBox txt = new TextBox();
e.Row.Cells[i].Controls.Add(txt);
}
}
}

You can try with this modified RowDataBound event handler:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
for (int i = 1; i < e.Row.Cells.Count; i++) // Does not process the first cell
{
TextBox txt = new TextBox();
TableCell cell = e.Row.Cells[i];
txt.Text = cell.Text.Replace(" ", ""); // Removes
cell.Text = "";
cell.Controls.Add(txt);
}
}
e.Row.Cells.RemoveAt(0); // Removes the first cell in the row
}

Add new row in gridview while button onclick

This is my program that page load the gridview and retrieve the database record to textbox and i put a add new button wish to add new row exactly like that row but the textbox is empty.
I wanted to create a new row in GridView while click add new button while my TextBox is retrieve data from database. I try to run the code but it is nothing happen when i click the button. Hope someone may help. Thanks.
My front end code
<Columns>
<asp:TemplateField HeaderStyle-CssClass="display_none">
<ItemTemplate>
<asp:Label ID="Label3" runat="server" Font-Bold="true" Font-Size="Medium">Name</asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderStyle-CssClass="display_none">
<ItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" CssClass="NormalInputTextField" Text='<%#Eval("SLMN") %>'></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderStyle-CssClass="display_none">
<ItemTemplate>
<asp:Button ID="BtnDelete" runat="server" Text="Delete" CssClass="btn btn-primary" CommandName="remove" CommandArgument='<%# Container.DataItemIndex %>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField FooterStyle-BorderStyle="None" HeaderStyle-CssClass="display_none">
<ItemTemplate>
<asp:Button ID="BtnSearch2" runat="server" Text="Search" CssClass="btn btn-primary" CommandName="ViewComments" OnClientClick="javascript:saveData(this,'grid')"/>
</ItemTemplate>
<FooterStyle HorizontalAlign="Right" BorderStyle="None"/>
<FooterTemplate>
<asp:Button ID="BtnAdd" runat="server" Text="Add New Row" CssClass="btn btn-primary" OnClick="ButtonAdd_Click"/>
</FooterTemplate>
</asp:TemplateField>
</Columns>
My back end code
private void AddNewRowToGrid()
{
DataTable dt = new DataTable();
DataRow dr = null;
dt.Columns.Add(new DataColumn("Column1", typeof(string)));
dt.Columns.Add(new DataColumn("Column2", typeof(string)));
dr = dt.NewRow();
dr["Column1"] = string.Empty;
dr["Column2"] = string.Empty;
dt.Rows.Add(dr);
}
My onclick event to call add new function
protected void ButtonAdd_Click(object sender, EventArgs e)
{
AddNewRowToGrid();
}
My gridview tag
<grd:MultiSelectGridView ID="grid2" runat="server" Width="500px"
CssClass="paging_gridview" AllowPaging="True"
AutoGenerateColumns ="false" PageSize="10" PagerType="Custom"
ShowFooter="true" OnRowDeleting="grid2_RowDeleting"
MultiSelectDataKeyName="Urid,Name" ShowHeaderWhenEmpty="true"
MultiSelectColumnIndex="0" EnableMultiSelect="false" GridLines="None" BorderStyle="None" OnRowCommand="grid2_RowCommand"
>
i bind my record to gridview by page load
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
Loadgrid();
}
}
private void Loadgrid()
{
string branch = txtBranch.Text.Trim();
string name = txtName.Text.Trim();
string sql = "SELECT * FROM fcs_cotmdl WHERE TMDL= '" + name + "'AND CONO='" + branch + "' ";
SqlDataSource2.ConnectionString = ConfigurationManager.ConnectionStrings["ConnStr_epsi"].ConnectionString;
SqlDataSource2.ConnectionString = SqlDataSource2.ConnectionString.Replace("Provider=OraOLEDB.Oracle.1;", "");
SqlDataSource con = new SqlDataSource();
SqlDataSource2.SelectCommand = sql;
grid2.DataSourceID = "SqlDataSource2";
grid2.DataBind();
}

Following tutorial details the exact same scenario. Please refer to it.
Adding Dynamic Rows to Gridview on Button Click
private void AddNewRowToGrid()
{
int rowIndex = 0;
if (ViewState["CurrentTable"] != null)
{
DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
DataRow drCurrentRow = null;
if (dtCurrentTable.Rows.Count > 0)
{
for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
{
//extract the TextBox values
TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
//Instead of all the textboxes, use the button as you require.
drCurrentRow = dtCurrentTable.NewRow();
drCurrentRow["RowNumber"] = i + 1;
dtCurrentTable.Rows[i - 1]["Column1"] = box1.Text;
dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;
rowIndex++;
}
dtCurrentTable.Rows.Add(drCurrentRow);
ViewState["CurrentTable"] = dtCurrentTable;
Gridview1.DataSource = dtCurrentTable;
Gridview1.DataBind();
}
}
else
{
Response.Write("ViewState is null");
}
//Set Previous Data on Postbacks
SetPreviousData();
}
And then the SetPreviousData() Function:
private void SetPreviousData()
{
int rowIndex = 0;
if (ViewState["CurrentTable"] != null)
{
DataTable dt = (DataTable)ViewState["CurrentTable"];
if (dt.Rows.Count > 0)
{
for (int i = 0; i < dt.Rows.Count; i++)
{
TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
box1.Text = dt.Rows[i]["Column1"].ToString();
box2.Text = dt.Rows[i]["Column2"].ToString();
box3.Text = dt.Rows[i]["Column3"].ToString();
rowIndex++;
}
}
}
}
Then inside your Click Event:
protected void ButtonAdd_Click(object sender, EventArgs e)
{
AddNewRowToGrid();
}

From your Load grid method you should retrieve the data as a data table and bind to grid. And save in in session. Like this:
private void Loadgrid()
{
var dt = new DataTable();
using (var conn = new SqlConnection (ConfigurationManager.ConnectionStrings["ConnectionStringName"].ToString()))
{
var command = new SqlCommand();
command.Connection = conn;
command.CommandText = "SELECT * FROM [dbo].[T1]";
command.CommandType = CommandType.Text;
using (var adaptor = new SqlDataAdapter(command))
{
if (conn.State == ConnectionState.Closed) conn.Open();
adaptor.Fill(dt);
if (conn.State == ConnectionState.Open) conn.Close();
}
}
Session["ss"] = dt;
grid2.DataSource = dt;
grid2.DataBind();
}
private void AddNewRowToGrid()
{
DataTable dt = (DataTable) Session["ss"];
DataRow dr = null;
DataRow newBlankRow1 = dt.NewRow();
dt.Rows.Add(newBlankRow1);
grid2.DataSource = dt;
grid2.DataBind();
Session["ss"] = dt;
}
After add an empty row also you need to bind data to grid again.

how to delete from gridview without database "check to determine if the object is null before calling the method"

The ff are codes in my .cs file
private void BindGridview(int rowcount)
{
DataTable dt = new DataTable();
DataRow dr;
dt.Columns.Add(new System.Data.DataColumn("Code", typeof(String)));
dt.Columns.Add(new System.Data.DataColumn("Course", typeof(String)));
dt.Columns.Add(new System.Data.DataColumn("Credit", typeof(String)));
if (ViewState["CurrentData"] != null)
{
for (int i = 0; i < rowcount + 1; i++)
{
dt = (DataTable)ViewState["CurrentData"];
if (dt.Rows.Count > 0)
{
dr = dt.NewRow();
dr[0] = dt.Rows[0][0].ToString();
}
}
dr = dt.NewRow();
dr[0] = this.cboCourseCode.Text;
dr[1] = this.txtCourseName.Text;
dr[2] = this.txtCredit.Text;
dt.Rows.Add(dr);
}
else
{
dr = dt.NewRow();
dr[0] = this.cboCourseCode.Text;
dr[1] = this.txtCourseName.Text;
dr[2] = this.txtCredit.Text;
dt.Rows.Add(dr);
}
// If ViewState has a data then use the value as the DataSource
if (ViewState["CurrentData"] != null)
{
GridView1.DataSource = (DataTable)ViewState["CurrentData"];
GridView1.DataBind();
}
else
{
// Bind GridView with the initial data assocaited in the DataTable
GridView1.DataSource = dt;
GridView1.DataBind();
}
// Store the DataTable in ViewState to retain the values
ViewState["CurrentData"] = dt;
}
protected void BindGrid()
{
GridView1.DataSource = ViewState["dt"] as DataTable;
GridView1.DataBind();
}
protected void OnRowDeleting(object sender, GridViewDeleteEventArgs e)
{
int index = Convert.ToInt32(e.RowIndex);
DataTable dt = ViewState["dt"] as DataTable;
dt.Rows[e.RowIndex].Delete();
ViewState["dt"] = dt;
BindGrid();
}
protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
string Code = e.Row.Cells[0].Text;
foreach (Button button in e.Row.Cells[3].Controls.OfType<Button>())
{
if (button.CommandName == "Delete")
{
button.Attributes["onclick"] = "if(!confirm('Do you want to delete " + Code + "?')){ return false; };";
}
}
}
}
protected void cboCourseCode_SelectedIndexChanged(object sender, EventArgs e)
{
this.Populate_Course_Details();
}
protected void BtnAdd_Click(object sender, EventArgs e)
{
/* DataTable dt = new DataTable();
dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Code"), new DataColumn("Course"), new DataColumn("Credit") });
dt.Rows.Add(this.cboCourseCode.Text, this.txtCourseName.Text, this.txtCredit.Text);
ViewState["dt"] = dt;
BindGrid();*/
if (ViewState["CurrentData"] != null)
{
DataTable dt = (DataTable)ViewState["CurrentData"];
int count = dt.Rows.Count;
BindGridview(count);
}
else
{
BindGridview(1);
}
}
My aspx file also has this gridview
<asp:GridView ID="GridView1" CssClass = "Grid" runat="server" OnRowDeleting="OnRowDeleting" AutoGenerateColumns = "false" OnRowDataBound = "OnRowDataBound">
<Columns>
<asp:BoundField DataField="Code" HeaderText="Code" />
<asp:BoundField DataField="Course" HeaderText="Course" />
<asp:BoundField DataField="Credit" HeaderText="Credit" />
<asp:CommandField ShowDeleteButton="True" ButtonType="Button" />
</Columns>
</asp:GridView>
When I start to delete, I get this error:
check to determine if the object is null before calling the method

Error Reason
in OnRowDeleting function you are creating datatable and assigning viewstate["dt"],which doesn't have current data. that's why it shows Object is Null
Solution
Try This
First make one of the column as data key.consider i want to make "Code" column as datakey.
datakey will help to find specific row to delete
<asp:GridView ID="GridView1" CssClass = "Grid" runat="server" OnRowDeleting="OnRowDeleting" AutoGenerateColumns = "false" OnRowDataBound = "OnRowDataBound" DataKeyNames="Code">
After That in .cs code
create a datatable with currentdata
make "Code" column as primary key
find particular code(which you want to delete)using find()
then delete that row using delete() function
Reflect the deletion in viewsate["currentdata"]
then bind to gridview
protected void OnRowDeleting(object sender, GridViewDeleteEventArgs e)
{
string code = GridView1.DataKeys[e.RowIndex].Value.ToString();
if (ViewState["CurrentData"] != null)
{
DataTable dt = (DataTable)ViewState["CurrentData"];
dt.PrimaryKey = new DataColumn[] { dt.Columns["Code"] };
dt.Rows.Find(code).Delete();
ViewState["CurrentData"] = dt;
GridView1.DataSource = dt;
GridView1.DataBind();
}
}