TcxCustomComboBoxProperties.DropDownAutoWidth Property

Specifies if the drop-down window’s width is automatically adjusted according to content size.

Declaration

property DropDownAutoWidth: Boolean read; write; default True;

Property Value

Type	Default	Description
Boolean	True	True Default. The drop-down window’s width is adjusted automatically to fit the largest list item. The maximum width cannot exceed the editor width; the DropDownWidth property value is ignored. False The drop-down window’s width is fixed. You can use the DropDownWidth property to specify the required fixed drop-down width.

Remarks

You can set the DropDownAutoWidth property to False and use the DropDownWidth property to define a fixed pixel width for the editor’s drop-down window.

To modify the number of simultaneously visible items in the drop-down window, use the DropDownRows property.

Code Example: Populate the Combo Box Menu from a Dataset Field

The code example in this section does the following:

• Assigns a TcxComboBox as an in-place editor to the Names column in a data-aware Data Grid View.
• Populates the editor’s drop-down window with values from the underlying dataset field.

Tip

If you need to add a user input string as a new combo box item, handle the OnNewLookupDisplayText event.

How to Test this Code Example

Follow the steps below to test this code example in your RAD Studio IDE:

1. Copy the DFM code example in this section.
2. Create a new project in the IDE and focus an empty form.
3. Press Ctrl + V to populate the form with preconfigured components.
4. Create an empty OnCreate event handler for the form and paste the code example into the handler.
5. Add the cxDropDownEdit unit to the uses clause and run the project.

DFM

  object cxGrid1: TcxGrid
   Left = 72
   Top = 80
   Width = 545
   Height = 200
   TabOrder = 0
   object cxGrid1DBTableView1: TcxGridDBTableView
     Navigator.Buttons.CustomButtons = <>
     ScrollbarAnnotations.CustomAnnotations = <>
     DataController.DataSource = DataSource1
     DataController.Summary.DefaultGroupSummaryItems = <>
     DataController.Summary.FooterSummaryItems = <>
     DataController.Summary.SummaryGroups = <>
     object cxGrid1DBTableView1RecId: TcxGridDBColumn
       DataBinding.FieldName = 'RecId'
       Visible = False
     end
     object cxGrid1DBTableView1Groups: TcxGridDBColumn
       DataBinding.FieldName = 'Groups'
     end
     object cxGrid1DBTableView1Names: TcxGridDBColumn
       DataBinding.FieldName = 'Names'
     end
     object cxGrid1DBTableView1Values: TcxGridDBColumn
       DataBinding.FieldName = 'Values'
       Width = 54
    end
   end
   object cxGrid1Level1: TcxGridLevel
     GridView = cxGrid1DBTableView1
   end
 end
 object dxMemData1: TdxMemData
   Active = True
   Indexes = <>
   Persistent.Data = {
     5665728FC2F5285C8FFE3F04000000140000000100070047726F757073001400
     0000010006004E616D657300040000000300070056616C756573000400000009
     000600446174657300010600000047726F75703101050000004E616D6531010A
     000000017B000B00010600000047726F75703101050000004E616D6532011400
     000001CF0E0B00010600000047726F75703201050000004E616D6533011E0000
     00017A210B00010600000047726F75703201050000004E616D65340128000000
     01892B0B00}
   SortOptions = []
   Left = 520
   Top = 88
   object dxMemData1Groups: TStringField
     FieldName = 'Groups'
   end
   object dxMemData1Names: TStringField
     FieldName = 'Names'
   end
   object dxMemData1Values: TIntegerField
     FieldName = 'Values'
   end
   object dxMemData1Dates: TDateField
     FieldName = 'Dates'
   end
 end
 object DataSource1: TDataSource
   DataSet = dxMemData1
   Left = 472
   Top = 176
 end

Delphi

uses
  cxDropDownEdit;  // Declares the TcxComboBoxProperties class
// ...

procedure TMyForm.FormCreate(Sender: TObject);
var
  AProperties: TcxComboBoxProperties;
begin
  // Assign a combo box as an in-place editor for the "Names" grid column
  cxGrid1DBTableView1Names.PropertiesClass := TcxComboBoxProperties;
  AProperties := cxGrid1DBTableView1Names.Properties as TcxComboBoxProperties;
  AProperties.BeginUpdate;  // Initiates the following batch operation
  try
    AProperties.Sorted := True;  // Sorts prepopulated values
    AProperties.DropDownListStyle := lsFixedList;  // Limits user input to the prepoulated list
    AProperties.DropDownAutoWidth := False;  // Disables automatic menu width adjustment
    AProperties.DropDownWidth := 105;  // Sets a fixed drop-down menu width
    // Populate the combo box editor's drop-down menu from the "Names" dataset field
    dxMemData1.DisableControls;
    try
      dxMemData1.First;
      while not dxMemData1.Eof do
      begin
        AProperties.Items.Add(dxMemData1.FieldByName('Names').AsString);
        dxMemData1.Next;
      end;
      dxMemData1.First;
    finally
      dxMemData1.EnableControls;
    end;
  finally
    AProperties.EndUpdate;  // Calls EndUpdate regardless of the batch operation's success
  end;
end;

C++

#include "cxDropDownEdit.hpp"  // Declares the TcxComboBoxProperties class

// Add the following linker directive to the corresponding CPP source file:
#pragma link "cxDropDownEdit"  // Required to use cxDropDownEdit declarations

void __fastcall TMyForm::FormCreate(TObject *Sender)
{
  TcxComboBoxProperties *AProperties;
  // Assign a combo box as an in-place editor for the "Names" grid column
  cxGrid1DBTableView1Names->PropertiesClass = __classid(TcxComboBoxProperties);
  AProperties = dynamic_cast<TcxComboBoxProperties*>(cxGrid1DBTableView1Names->Properties);
  AProperties->BeginUpdate();  // Initiates the following batch operation
  try
  {
    AProperties->Sorted = true;  // Sorts prepopulated values
    AProperties->DropDownListStyle = lsFixedList;  // Limits user input to the prepopulated list
    AProperties->DropDownAutoWidth = false;  // Disables automatic menu width adjustment
    AProperties->DropDownWIdth = 105;  // Sets a fixed drop-down menu width
    // Populate the combo box editor's drop-down menu from the "Names" dataset field
    dxMemData1->DisableControls();
    try
    {
      dxMemData1->First;
      do
      {
        AProperties->Items->Add(dxMemData1->FieldByName("Names")->AsString);
        dxMemData1->Next();
      } while(!dxMemData1->Eof);
    }
    __finally
    {
      dxMemData1->EnableControls();
    }
  }
  __finally
  {
    AProperties->EndUpdate();  // Calls EndUpdate regardless of the batch operation's success
  }
}

Default Value

The DropDownAutoWidth property’s default value is True.