ComboBox

The ComboBox control is frequently used when the user must input information which is chosen from a predetermined list.

	Key properties:	Data Field, Items, Lookup Data Source, Lookup Data Field, Lookup Text Field, Lookup Max Records
	Key events:	On Click, On Change
	Server Code:	ComboBox = Class(ButtonEditor)
	Browser Code:	ComboBox = Class(ButtonEditor)

States	Appearance	Description
Normal		The default state for the control when no other state is active.
Mouseover		This view is displayed when the user moves the cursor over the control
Focused		This view is displayed when the control's ability to receive input is disabled.
Disabled		This view is displayed when the control's ability to receive input is disabled.

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Data Binding

Use Data Field property to bound ComboBox control to the data source allowing to display information associated with a field in the Data Source. CombotBox bound to the Data Source in a single form mode will display all records available in the current page of the Dataset.

ComboBox can be configured to display list of items from lookup data source. You either need to set Data Field property to Relationship field, or set Lookup Data Source, Lookup Data Field and Lookup Text Field individually.

Use ComboBox "Refresh" method to re-read items from lookup data source if it represents a parametric query. This method is particularly useful when items of a parametric databound ComboBox needs updating based on a criteria or data supplied by a user. For example if there are two ComboBoxes used for presenting "Countries" and "States" and the items in the States ComboBox needs updating based on the selected country. The use of Refresh method is shown in the following example:

FX Code

Procedure frmRegister.comboCountryChange(Event: TDOMEvent);
Begin
    comboStates.Refresh('"prmCountry=' + comboCountry.Items[comboCountry.ItemIndex] + '"');
End;

Published Message Sub comboCountryChange(Event As TDOMEvent)
   ComboStates.Refresh(#34"prmCountry=" + comboCountry.Items(comboCountry.ItemIndex) + #34)
End Sub

published message void comboCountryChange(TDOMEvent Event)
{
    ComboStates.Refresh("\"prmCountry=" + comboCountry.Items[comboCountry.ItemIndex] + "\"");
}

The items (States) in the ComboStates Combobox are updated (using Refresh method) on the OnChange event of the comboCountry ComboBox.

Run-time behavior

You can manipulate with ComboBox items programmaticaly both in Server side and Browser side.

Server-Side Syntax

FX Code

Procedure Form1.ComboBox1BeforePrint(Sender: TWebControl; Canvas: TWebCanvas; Var Print: Boolean);
Begin
    ComboBox1.Items.Add('Red');
    ComboBox1.Items.Add('Green');
    ComboBox1.Items.Add('Blue');
End;

Published Message Sub ComboBox1BeforePrint(Sender As TWebControl, Canvas As TWebCanvas, ByRef Print As Boolean)
  ComboBox1.Items.Add("Red")
  ComboBox1.Items.Add("Green")
  ComboBox1.Items.Add("Blue")
End Sub

published message void ComboBox1BeforePrint(TWebControl Sender, TWebCanvas Canvas, ref Boolean Print)
{
  ComboBox1.Items.Add("Red");
  ComboBox1.Items.Add("Green");
  ComboBox1.Items.Add("Blue");
}

Browser-Side Syntax

FX Code

  ComboBox1.Add('Red');
  ComboBox1.Add('Green');
  ComboBox1.Add('Blue');

  ComboBox1.Add("Red")
  ComboBox1.Add("Green")
  ComboBox1.Add("Blue")

  ComboBox1.Add("Red");
  ComboBox1.Add("Green");
  ComboBox1.Add("Blue");

• Controls