Object must implement IConvertible

Object must implement IConvertible.
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.InvalidCastException: Object must implement
IConvertible.

Error Detail Line 279:
da.InsertCommand.Parameters.Add(“@Total”, SqlDbType.Int).Value =
txttotal.Text; Line 280: con1.Open(); Line 281:
da.InsertCommand.ExecuteNonQuery();

Code:

SqlDataAdapter da = new SqlDataAdapter();
    da.InsertCommand = new SqlCommand("Insert Into customer_order(ProductID,product_Name,Product_Type,Weight,Unit_Price,No_Of_Master_Pack,Master_Pack_Price,Quantity,Total)VALUES(@ProductID,@product_Name,@Product_Type,@Weight,@Unit_Price,@No_Of_Master_Pack,@Master_Pack_Price,@Quantity,@Total)", con1);
    da.InsertCommand.Parameters.Add("@ProductID",SqlDbType.VarChar).Value=DropDownList3.SelectedItem;
    da.InsertCommand.Parameters.Add("@product_Name",SqlDbType.VarChar).Value=DropDownList2.SelectedItem;
    da.InsertCommand.Parameters.Add("@Product_Type", SqlDbType.VarChar).Value = DropDownList1.SelectedItem;
    da.InsertCommand.Parameters.Add("@Weight",SqlDbType.Int).Value=txtwgt.Text;
    da.InsertCommand.Parameters.Add("@Unit_Price",SqlDbType.Int).Value=txtmrpsinglepack.Text;
    da.InsertCommand.Parameters.Add("@No_Of_Master_Pack",SqlDbType.Int).Value=txtnoofmasterpack.Text;
    da.InsertCommand.Parameters.Add("@Master_Pack_Price",SqlDbType.Int).Value=txtmrpmaster.Text;
    da.InsertCommand.Parameters.Add("@Quantity",SqlDbType.Int).Value=txtquantity.Text;
    da.InsertCommand.Parameters.Add("@Total", SqlDbType.Int).Value = txttotal.Text;
con1.Open();
da.InsertCommand.ExecuteNonQuery();

Answers:

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Method 1

ListControl.SelectedItem returns a ListItem – and it doesn’t make much sense for the value of a parameter to be a list item itself, but instead the item’s value or text. You probably want something like:

da.InsertCommand.Parameters
  .Add("@ProductID",SqlDbType.VarChar).Value = DropDownList3.SelectedItem.Text;

or

da.InsertCommand.Parameters
  .Add("@ProductID",SqlDbType.VarChar).Value = DropDownList3.SelectedItem.Value;

Method 2

use DropDownList3.SelectedItem.Text or DropDownList3.SelectedItem.Value to assign it to a Value.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0