CODEWITHSUNDEEP
c#asp.netvisual-studiodrop-down-menu
user123456789
user123456789

Reputation: 2004

how to get value selected in dropdownlist before change was made?

I have a dropdownlist with with a few options. When the user changes one of these options in the dropdownlist, I want to create a note. The problem is I want the note to say what change was made. So for example this code creates a note when the currency dropdownlist is changed. So if the current value is "Euro" and the user changes it to "Sterling" I want the note to say "currency changed from Euro to Sterling" etc. I know by using selectedItem I can get the new value selected, but how to I get the value that was in the dropdownlist before the change was made?

if (cust.Currency.ToString() != ddlCustomerCurrency.SelectedItem.Text)
   {
        Customer.Notes.InsertNote(cust.ID, Company.Current.CompanyID, DateTime.Now, "Currency changed from '" + /*Previous value */ + "' to '" + ddlCustomerCurrency.SelectedItem.Text + "'", CurrentUser.UserID, 1);
   }

Upvotes: 0

Views: 2031

Answers (2)

Cetin Basoz
Cetin Basoz

Reputation: 23867

You can save the current value to ddlDropDown's tag property, so you would always have the last selected value as 'previous value' there.

Sample:

void Main()
{
  var currencies = new List<Currency>() {
   new Currency { Code="EUR", Name="Euro"},
   new Currency { Code="USD", Name="US Dollars"},
   new Currency { Code="AUD", Name="Australian Dollars"},
   new Currency { Code="JPY", Name="Japanese Yen"},
  };

  var customer = new Customer { Id=1, Currency="", Notes=new List<string>()};

  Form f = new Form {Text="Sample"};
  ComboBox ddlCustomerCurrency = new ComboBox { Top=10, Left=10, Tag="", 
      DataSource=currencies, DisplayMember="Name"};
  Button b = new Button {Text = "Show Customer Notes", Top=60, Left = 10};    

  f.Controls.Add(ddlCustomerCurrency);
  f.Controls.Add(b);

  ddlCustomerCurrency.SelectedIndexChanged += (sender, args) => {
    var cmb = sender as ComboBox;
    if (cmb != null)
    {
      var currency = cmb.SelectedItem as Currency;
      var oldValue= cmb.Tag;
      if ( currency != null && oldValue != currency.Name )
      {
        customer.Notes.Add( string.Format(
          "\nOld Currency:{0}, New Currency:{1}, Ticks:{2}",
           oldValue, currency.Name, DateTime.Now.Ticks) );
        cmb.Tag = currency.Name;
      }
    }
  };

  b.Click += (sender,args) => {
    if (customer.Notes.Any ())
      MessageBox.Show( customer.Notes.Last () );
  };

  f.Show();
}

class Currency
{
  public string Code { get; set; }
  public string Name { get; set; }
}

class Customer
{
  public int Id { get; set; }
  public string Currency { get; set; }
  public List<string> Notes { get; set; }
}

Upvotes: 0

sara
sara

Reputation: 3609

You can store the initial and subsequent values of the dropdown in-memory. Then, every time the OnChange event is called, simply look at the "current" value and compare it to the value sent to the OnChange handler.

EDIT: something like this might do the trick:

public class MyClass
{
    private string _currentSelectedCurrency;

    public void DdlCustomerCurrency_OnChange(object sender, EventArgs e)
    {
        if (cust.Currency.ToString() != ddlCustomerCurrency.SelectedItem.Text)
        {
            Customer.Notes.InsertNote(cust.ID, Company.Current.CompanyID, DateTime.Now, "Currency changed from '" + _currentSelectedCurrency +"' to '" + ddlCustomerCurrency.SelectedItem.Text + "'", CurrentUser.UserID, 1);
            _currentSelectedCurrency = ((DropDownList) sender).Text
        }
    }
}

Upvotes: 2

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