Object cannot be cast from DBNull to other types for Double Data Type

0
votes

I am seeing error when there is null value in database for any cell, Object cannot be cast from DBNull to other types. - Asp.net grid view

<asp:TemplateField ItemStyle-Width="120" HeaderText="Price Difference">
                                     <ItemTemplate>
<%# PercentageChange(DataBinder.Eval(Container.DataItem, "FirstPrice"),DataBinder.Eval(Container.DataItem, "SecondPrice")) %>

                                     </ItemTemplate>
                                 </asp:TemplateField>

C# 

protected string PercentageChange(object client_Price, object second_price)
    {
       double price1 = Convert.ToDouble(client_Price);
            double price2 = Convert.ToDouble(second_price);
            double percentagechange = ((price1 - price2) / price2) * 100;
             return percentagechange ;
}
3
c#asp.net
Oh DBNull, how much do I loathe thee? Let me count the ways... stackoverflow.com/a/9632050/23354 - Marc Gravell
I do have another problem, let's say price1 is a property of dbml table, tagged as bit and is placed at column 7 of datagridview.. bool canViewInOut = (dataGridView1.Rows[i].Cells[7].Value == DBNull.Value || !Convert.ToBoolean(dataGridView1.Rows[i].Cells[7].Value)) ? false : true; - Juran

3 Answers

3
votes

You need to compare you values with DBNull.Value as follow

protected string PercentageChange(object client_Price, object second_price)
{
       if(client_price==DBNull.Value)
       {
           .....
       }
       //double price1 = Convert.ToDouble(client_Price);
       //double price2 = Convert.ToDouble(second_price);
       //double percentagechange = ((price1 - price2) / price2) * 100;
       //return percentagechange ;
 }
2
votes

Then check if it's DBNull or null:

protected string PercentageChange(object client_Price, object second_price)
{
    if(DBNull.Value.Equals(client_Price) || client_Price == null || DBNull.Value.Equals(second_price) || second_price == null)
        return "N/A"; // or whatever

    double price1 = Convert.ToDouble(client_Price);
    double price2 = Convert.ToDouble(second_price);
    double percentagechange = ((price1 - price2) / price2) * 100;
    return percentagechange.ToString();
}
0
votes

Reason for the error: In an object-oriented programming language, null means the absence of a reference to an object. DBNull represents an uninitialized variant or nonexistent database column. Source:MSDN

Actual Code which I faced error:

Before changed the code: 

        if( ds.Tables[0].Rows[0][0] == null ) //   Which is not working

         {
                seqno  = 1; 
          }
        else
        {
              seqno = Convert.ToInt16(ds.Tables[0].Rows[0][0]) + 1;
         }

After changed the code: 

   if( ds.Tables[0].Rows[0][0] == DBNull.Value ) //which is working properly
        {
                    seqno  = 1; 
         }
            else
            {
                  seqno = Convert.ToInt16(ds.Tables[0].Rows[0][0]) + 1;
             }

Conclusion: when the database value return the null value, we recommend to use the DBNull class instead of just specifying as a null like in C# language.