Delphi VCL Custom TCombobox Dropdown Width

In Delphi VCL, the dropdown width of a TComboBox control is determined by the width of the TComboBox itself. By default, the dropdown width matches the width of the combobox control. However, if you want to customize the dropdown width independently, you can achieve it by creating a custom TComboBox control and overriding its behavior.

Here's an example of how you can create a custom TComboBox control with a custom dropdown width:

1. Create a new unit (e.g., CustomComboBox.pas) and add the following code:

delphiCopy code
unit CustomComboBox;



interface



uses

  System.Classes, Vcl.Controls, Vcl.StdCtrls;



type

  TCustomComboBox = class(Vcl.StdCtrls.TComboBox)

  private

    FDropDownWidth: Integer;

  protected

    procedure DropDown; override;

  public

    property DropDownWidth: Integer read FDropDownWidth write FDropDownWidth;

  end;



implementation



{ TCustomComboBox }



procedure TCustomComboBox.DropDown;

begin

  if FDropDownWidth > 0 then

    Perform(CB_SETDROPPEDWIDTH, FDropDownWidth, 0);

  inherited DropDown;

end;



end.

1. Save the unit and add it to your project.

2. Now, you can use the TCustomComboBox control on your form instead of the default TComboBox control. Set the DropDownWidth property of the TCustomComboBox to the desired width for the dropdown list.

By using the TCustomComboBox control, you can set a specific width for the dropdown list independently of the width of the combobox itself.