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

Question

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

Answer 1

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 ;
 } 

Answer 2

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();
} 

Answer 3

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.