向数据表添加新行时出现错误

Question

I want to make stacked area chart in Run Time. I want to add datapoints when i click button.

However getting an error ' this row already belongs to another table '.

Here is the full code of Simple Project;

DataRow drIBM, drMSN, drMCN;
DataTable chartData = new DataTable();
Random r = new Random();
int count = 0;

protected void Page_Load(object sender, EventArgs e)
{
    chartData.Columns.Add("Series Label", typeof(string));

    for (int i = 0; i < 10; i++)
    {
        chartData.Columns.Add("DP_" + i.ToString(), typeof(int)); // Addind Datapoints as a Columns
    }

    drIBM = chartData.NewRow();
    drMSN = chartData.NewRow();
    drMCN = chartData.NewRow();

    drIBM["Series Label"] = "IBM";
    drMSN["Series Label"] = "MSN";
    drMCN["Series Label"] = "MCN";

    if (Session["chartData"] == null)
    {
        Session["chartData"] = chartData;
    }

}

protected void Button1_Click(object sender, EventArgs e)
{
    count++;

    chartData = Session["chartData"] as DataTable;

    drIBM[count] = r.Next(1, 10); // Datarow[Column Index] getting random number
    drMSN[count] = r.Next(1, 10);
    drMCN[count] = r.Next(1, 10);

    chartData.Rows.Add(drIBM); // In this part I am getting above error.
    chartData.Rows.Add(drMSN);
    chartData.Rows.Add(drMCN);

    Session["chartData"] = chartData;
    UltraChart1.DataSource = Session["chartData"];
    UltraChart1.DataBind();
}

Answer 1

I'm not hugely familiar with the inner workings of the DataRow class but I'm guessing it holds a reference to chartData at the time you call chartData.NewRow();

In Button1_Click() you are replacing this reference with one to an object held in your Session object. Even though semantically identical to chartData , the DataRow believes this is a different object and thus throws the exception.

Considering chartData seems to be a class variable, I'm not sure why you are bothering with Session at all. Try removing the following line and see if this works:

chartData = Session["chartData"] as DataTable;

Answer 2

You have declared Row variables globally. If you change the scope of these variable to local ie remove the declaration of these DataRow variables from the top and declare those again in methods.(eg declare DataRow drIBM, drMSN, drMCN; in specific methods like Page_Load and Button_Click1) should solve the issue.