C# adding empty row to GridView

Question

Small issue I'm having with my code I can't fix. I have a GridView with a ImageButton which should add a new empty row. For some reason I get this error:

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.] CTI_DFC.Default.gv_Steps_RowCommand(Object sender, GridViewCommandEventArgs e) +469
System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +172
System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +163 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +83
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3771

So this is the GridView I have:

<asp:GridView ID="gv_Steps" runat="server" CssClass="lbl_user" Font-Names="Verdana" Font-Size="10px" HeaderStyle-Height="23.5px" HorizontalAlign="Center" 
    RowStyle-Height="23.5px" ShowHeaderWhenEmpty="True" style="z-index: 1; left: 8px; top: 143px; position: absolute; height: 20px; width: 1178px;" AutoGenerateColumns="False" OnRowCommand="gv_Steps_RowCommand">
    <AlternatingRowStyle BackColor="#DCE4FF" />
    <Columns>
        <asp:TemplateField HeaderText="Step" HeaderStyle-HorizontalAlign="Left" >
            <ItemTemplate>
                <asp:TextBox ID="txt_Step" HeaderStyle-HorizontalAlign="Left" runat="server" Width="150px" Text='<%# Bind("Step") %>'/>
            </ItemTemplate>
        </asp:TemplateField> 
        <asp:TemplateField HeaderText="Server" HeaderStyle-HorizontalAlign="Left" >
            <ItemTemplate>
                <asp:TextBox ID="txt_Server" HeaderStyle-HorizontalAlign="Left" runat="server" Width="150px" Text='<%# Bind("Server") %>'/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Type" HeaderStyle-HorizontalAlign="Left" >
            <ItemTemplate>
                <asp:TextBox ID="txt_Type" HeaderStyle-HorizontalAlign="Left" runat="server" Width="150px" Text='<%# Bind("Type") %>'/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Job" HeaderStyle-HorizontalAlign="Left" >
            <ItemTemplate>
                <asp:TextBox ID="txt_Job" HeaderStyle-HorizontalAlign="Left" runat="server" Width="150px" Text='<%# Bind("Job") %>'/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Number" HeaderStyle-HorizontalAlign="Left" >
            <ItemTemplate>
                <asp:TextBox ID="txt_Number" HeaderStyle-HorizontalAlign="Left" runat="server" Width="150px" Text='<%# Bind("Number") %>'/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="" ItemStyle-Width="15px" ItemStyle-Wrap="false">
            <ItemTemplate>
                <asp:ImageButton ID="btn_AddRow" runat="server" AlternateText="Add Row" CommandArgument="<%# Container.DataItemIndex %>" CommandName="Add" ImageUrl="./Img/ADD.png" ToolTip="Add Row without Change" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="" ItemStyle-Width="15px" ItemStyle-Wrap="false">
            <ItemTemplate>
                <asp:ImageButton ID="btn_DeleteRow" runat="server" AlternateText="Delete Row" CommandArgument="<%# Container.DataItemIndex %>" CommandName="Delete" ImageUrl="./Img/DEL.png" ToolTip="Delete Row without Change" />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
    <HeaderStyle BackColor="#0B4DA2" Font-Bold="True" ForeColor="White" />
    <RowStyle Height="23px" />
</asp:GridView>

And this is the C# code how I'm trying to do it:

protected void gv_Steps_RowCommand(object sender, GridViewCommandEventArgs e)
{
    int intIndex = Convert.ToInt32(e.CommandArgument);  //will be used for Delete

    if (e.CommandName == "Delete" && (gv_Steps.Rows.Count > 1))
    {
        //Nothing done yet
    }
    if (e.CommandName == "Add")
    {
        DataTable dt = gv_Steps.DataSource as DataTable;
        DataRow dr = dt.NewRow();
        dt.Rows.Add(dr);

        gv_Steps.DataSource = dt;
        gv_Steps.DataBind();
    }
}

Thanks for any advice!

EDIT

I understand now that my DataTable is empty and doesn't work like that, but how can I get GridView to DataSet and back with new empty row? I tried it like this with same error:

protected void gv_Steps_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        int intIndex = Convert.ToInt32(e.CommandArgument);  //will be used for Delete

        if (e.CommandName == "Delete" && (gv_Steps.Rows.Count > 1))
        {
            //Nothing done yet
        }
        if (e.CommandName == "Add")
        {
            DataTable dt = GridviewToDataTable();
            DataRow dr = dt.NewRow();
            dt.Rows.Add(dr);

            gv_Steps.DataSource = dt;
            gv_Steps.DataBind();
        }
    }

private DataTable GridviewToDataTable()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add(new DataColumn("Step", typeof(string)));
        dt.Columns.Add(new DataColumn("Server", typeof(string)));
        dt.Columns.Add(new DataColumn("Type", typeof(string)));
        dt.Columns.Add(new DataColumn("Job", typeof(string)));
        dt.Columns.Add(new DataColumn("Number", typeof(string)));

        foreach (GridViewRow row in gv_Steps.Rows)
        {
            dt.Rows.Add();
            dt.Rows[row.RowIndex][0] = ((TextBox)row.FindControl("Step")).Text;
            dt.Rows[row.RowIndex][1] = ((TextBox)row.FindControl("Server")).Text;
            dt.Rows[row.RowIndex][2] = ((TextBox)row.FindControl("Type")).Text;
            dt.Rows[row.RowIndex][3] = ((TextBox)row.FindControl("Job")).Text;
            dt.Rows[row.RowIndex][4] = ((TextBox)row.FindControl("Number")).Text;
        }

        return dt;
    }

Error i get:

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.] CTI_DFC.Default.GridviewToDataTable() +1161
CTI_DFC.Default.gv_Steps_RowCommand(Object sender, GridViewCommandEventArgs e) +392
System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +172
System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +163 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +83
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3771

EDIT 2

Tried it like this:

protected void gv_Steps_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        int intIndex = Convert.ToInt32(e.CommandArgument);  //will be used for Delete

        if (e.CommandName == "Delete" && (gv_Steps.Rows.Count > 1))
        {
            //Nothing done yet
        }
        if (e.CommandName == "Add")
        {
            DataTable dt = GridviewToDataTable(gv_Steps);
            DataRow dr = dt.NewRow();
            dt.Rows.Add(dr);

            gv_Steps.DataSource = dt;
            gv_Steps.DataBind();
            GridviewToDataTable(gv_Steps);
        }
    }
private DataTable GridviewToDataTable(GridView gv)
    {
        DataTable dt = new DataTable();
        dt.Columns.Add(new DataColumn("Step", typeof(string)));
        dt.Columns.Add(new DataColumn("Server", typeof(string)));
        dt.Columns.Add(new DataColumn("Type", typeof(string)));
        dt.Columns.Add(new DataColumn("Job", typeof(string)));
        dt.Columns.Add(new DataColumn("Number", typeof(string)));
        foreach (GridViewRow row in gv.Rows)
        {
            dt.Rows.Add();
            dt.Rows[row.RowIndex][0] = ((TextBox)row.FindControl("Step")).Text;
            dt.Rows[row.RowIndex][1] = ((TextBox)row.FindControl("Server")).Text;
            dt.Rows[row.RowIndex][2] = ((TextBox)row.FindControl("Type")).Text;
            dt.Rows[row.RowIndex][3] = ((TextBox)row.FindControl("Job")).Text;
            dt.Rows[row.RowIndex][4] = ((TextBox)row.FindControl("Number")).Text;
        }
        gv.DataSource = dt;
        gv.DataBind();
        return dt;
    }

Error I get:

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.] CTI_DFC.Default.GridviewToDataTable(GridView gv) +1145
CTI_DFC.Default.gv_Steps_RowCommand(Object sender, GridViewCommandEventArgs e) +407
System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +172
System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +163 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +83
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3771

Any other advice?

SOLUTION

I did it, got it done like this:

private DataTable GridviewToDataTable(GridView gv)
    {
        DataTable dt = new DataTable();
        dt.Columns.Add(new DataColumn("Step", typeof(string)));
        dt.Columns.Add(new DataColumn("Server", typeof(string)));
        dt.Columns.Add(new DataColumn("Type", typeof(string)));
        dt.Columns.Add(new DataColumn("Job", typeof(string)));
        dt.Columns.Add(new DataColumn("Number", typeof(string)));
        foreach (GridViewRow row in gv.Rows)
        {
            dt.Rows.Add();
            dt.Rows[row.RowIndex][0] = (row.FindControl("txt_Step") as TextBox).Text;
            dt.Rows[row.RowIndex][1] = (row.FindControl("txt_Server") as TextBox).Text;
            dt.Rows[row.RowIndex][2] = (row.FindControl("txt_Type") as TextBox).Text;
            dt.Rows[row.RowIndex][3] = (row.FindControl("txt_Job") as TextBox).Text;
            dt.Rows[row.RowIndex][4] = (row.FindControl("txt_Number") as TextBox).Text;
        }
        lbl_Fehlermeldung.Text = dt.Rows[0][0].ToString();
        lbl_Fehlermeldung.Visible = true;
        gv.DataSource = dt;
        gv.DataBind();
        return dt;
    }

`gv_Steps.DataSource` only works on initial load, not on PostBack. — VDWWD, Oct 18 '17 at 09:03

score 1 · Answer 1 · answered Oct 18 '17 at 09:01

1

Your Datasource is empty, this why your DataTable is converted to null object, and exception is throwed

answered Oct 18 '17 at 09:01

olpro123

39
7

Thanks, but how can I get my GridView to DataTable and back? See my Edit how i tried it.. – Tobe Oct 18 '17 at 09:14
can you show the exception after your edit? – olpro123 Oct 18 '17 at 09:19
Sorry forgot that one, added it. – Tobe Oct 18 '17 at 09:21
your gv_Steps object is null, maybe try to bind it again to datasource or hold it as global object – olpro123 Oct 18 '17 at 09:25
Tried to bind it again, failed. What do you mean exactly with "hold it as global object"? With Session[] or? – Tobe Oct 18 '17 at 09:36
Session or static – olpro123 Oct 18 '17 at 09:37
Can you give me an example with static please? – Tobe Oct 18 '17 at 09:39

score 0 · Answer 2 · answered Oct 18 '17 at 10:26

Your code is good for Empty gridview only. As you do not increment the row index.

For adding new row to the gridview has some concern.

Do you previously have some datasource in the gridview or not ? If you have some datasource previously and then you need to save the datasource in viewstate and before adding a new row you need to extract previous data in the gridview and then add a new row.

Follow below code

***First set initial row save datasource in viewstate

private void SetInitialRow()
{
    DataTable dt = new DataTable();
    DataRow dr = null;
    dt.Columns.Add(new DataColumn("RowNumber", 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)));
    dr = dt.NewRow();
    dr["RowNumber"] = 1;
    dr["Column1"] = string.Empty;
    dr["Column2"] = string.Empty;
    dr["Column3"] = string.Empty;
    dt.Rows.Add(dr);
    //dr = dt.NewRow();

    //Store the DataTable in ViewState
    ViewState["CurrentTable"] = dt;

    Gridview1.DataSource = dt;
    Gridview1.DataBind();
}

***set it in page_load

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        SetInitialRow(); 
    }
}

*** Add new row to gridview

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");

                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();
}

***Set previous data

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++;
            }
        }
    }
}

*** call on button click

 protected void ButtonAdd_Click(object sender, EventArgs e)
    {
        AddNewRowToGrid();
    }

Sorce link https://www.aspsnippets.com/Articles/Add-new-Row-to-GridView-on-Button-Click-in-ASPNet.aspx

C# adding empty row to GridView

2 Answers2