problem with table datasource

[jany]

hi everybody,
iam new to dotnet..
iam trying to give table as the datasource to the datagrid ,but iam getting an error like object ref.is not set to instance of an object...at the line r=dt.NewRow();
and i have no bound columns in my datagrid.my intension is to add the data entered in the textboxes to the grid though the datatable;
what is the error in my code.........
please help me..

protected DataTable dt = new DataTable();
DataRow r;
r = dt.NewRow();
r[0] = TextBox1.Text;
r[1] = TextBox2.Text;
r[2] = TextBox3.Text;
int i = DataGrid1.Items .Count;
dt.Rows.InsertA t (r,i );
dt.AcceptChange s();
dt.GetChanges() ;
DataGrid1.DataS ource = dt;
DataGrid1.DataB ind();

[jhardman]

moved to .NET forum

[Plater]

protected DataTable dt = new DataTable();
DataRow r;
r = dt.NewRow();

I think for .NewRow() to work, you have to have some concept of what the row would contain. And by that I mean you need to have columns defined before a .NewRow() can return a row.

[mikeyeli]

protected DataTable dt = new DataTable();
DataRow r;
r = dt.NewRow();

I think for .NewRow() to work, you have to have some concept of what the row would contain. And by that I mean you need to have columns defined before a .NewRow() can return a row.

Yup, the row is created based on the table schema, that is the reason why the NewRow() function is in the DataTable class, so like plater said, just add the columns first.

Besides its easy to index a column in a row according to a name

C#:

                  .
                  .
                  .
DataColumn column = new DataColumn("A");
DataTable table = new DataTable();
table.Columns.Add(column);
DataRow row = table.NewRow();
row["A"] = "Something";
table.Rows.Add(row);
                  .
                  .
someGrid.DataSource = table;
                  .
                  .
                  .

[jany]

Yup, the row is created based on the table schema, that is the reason why the NewRow() function is in the DataTable class, so like plater said, just add the columns first.

Besides its easy to index a column in a row according to a name

C#:

                  .
                  .
                  .
DataColumn column = new DataColumn("A");
DataTable table = new DataTable();
table.Columns.Add(column);
DataRow row = table.NewRow();
row["A"] = "Something";
table.Rows.Add(row);
                  .
                  .
someGrid.DataSource = table;
                  .
                  .
                  .

thanks for your reply mikeyeli .....
iam using the code this way....




public partial class tbgd : System.Web.UI.P age
{
protected DataTable dt = new DataTable();
DataRow dr;
protected void Page_Load(objec t sender, EventArgs e)
{
if (!Page.IsPostBa ck)
{
dt.Columns.Add( "Name", typeof(string)) ;
dt.Columns.Add( "Id", typeof(int));
}
}

protected void submit_Click(ob ject sender, EventArgs e)
{
dr = dt.NewRow();
dr["Name"] = "control value";
dr["Id"] = 12345;
dt.Rows.Add(dr) ;

DataGrid1.DataS ource = dt;
DataGrid1.DataB ind();
}
}


but iam getting column "Name" does not belongs to the table....
please tell me what is the problem with this code

[mzmishra]

Why you are adding the columns inside
if (!Page.IsPostBa ck)

[Shashi Sadasivan]

thanks for your reply mikeyeli .....
iam using the code this way....




public partial class tbgd : System.Web.UI.P age
{
protected DataTable dt = new DataTable();
DataRow dr;
protected void Page_Load(objec t sender, EventArgs e)
{
if (!Page.IsPostBa ck)
{
dt.Columns.Add( "Name", typeof(string)) ;
dt.Columns.Add( "Id", typeof(int));
}
}

protected void submit_Click(ob ject sender, EventArgs e)
{
dr = dt.NewRow();
dr["Name"] = "control value";
dr["Id"] = 12345;
dt.Rows.Add(dr) ;

DataGrid1.DataS ource = dt;
DataGrid1.DataB ind();
}
}


but iam getting column "Name" does not belongs to the table....
please tell me what is the problem with this code

I think the field name will be case sensitive. Check if there is anything more to that field name (copy paste the field name)

[jany]

Why you are adding the columns inside
if (!Page.IsPostBa ck)

because each time when the page postedback a new table is being created ,but i want to add the rows to the previous table rows,and the new row should be displayed along with the prev. one.....

[Plater]

That will not happen if you are creating the DataTable over and over again when the page_load happens.

[mikeyeli]

because each time when the page postedback a new table is being created ,but i want to add the rows to the previous table rows,and the new row should be displayed along with the prev. one.....

Programming web application is a little different than programming windows applications.

you should dedicate some time on reading about a webpage lifecycle. msdn has some good articles about this, that are very helpfull.

anyways, if what you want is, that that DataTable persists over postbacks, a not so clean way to do this, is simply making the data table static.