how auto size the columns width of a list view in virtual mode?

Question

When I use a TListView (ViewStyle = vsReport) I can autofit the width of the columns setting the LVSCW_AUTOSIZE or LVSCW_AUTOSIZE_USEHEADER values in the Width property of each column, now I start to use the Listview in virtual mode, but the width of the columns is not modified according to these values. So the question is : How I can adjust the width of the columns to fit to the content or header, when the lisvtiew is in virtual mode?

Answer 1

Since the list view in virtual mode don't know the item captions in advance (because it asks only for data of the visible area) it also cannot know the width of the widest one, so that's the reason why the autosize flag of the LVM_SETCOLUMNWIDTH behaves this way.

Thus the only way is to write a custom function which will query all your data, measure the text widths of all future captions and set the column width to the value of the widest one.

The following example shows how to do it. It uses the ListView_GetStringWidth macro for the text width calculations (it seems to be the most natural way to do this). However the problem is the value of the text padding. As it's stated in the documentation:

The ListView_GetStringWidth macro returns the exact width, in pixels, of the specified string. If you use the returned string width as the column width in a call to the ListView_SetColumnWidth macro, the string will be truncated. To retrieve the column width that can contain the string without truncating it, you must add padding to the returned string width.

But they didn't mention there how to get the padding value (and seems they won't to do so). Some people say (e.g. here) that it's enough to use 6 px for item's padding and 12 px for subitem's padding, but it isn't (at least for this example on Windows 7).

///////////////////////////////////////////////////////////////////////////////
/////   List View Column Autosize (Virtual Mode)   ////////////////////////////
///////////////////////////////////////////////////////////////////////////////

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, StdCtrls,
  Forms, Dialogs, StrUtils, ComCtrls, CommCtrl;

type
  TSampleRecord = record
    Column1: string;
    Column2: string;
    Column3: string;
  end;
  TSampleArray = array [0..49] of TSampleRecord;

type
  TForm1 = class(TForm)
    Button1: TButton;
    ListView1: TListView;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    SampleArray: TSampleArray;
    procedure AutoResizeColumn(const AListView: TListView;
      const AColumn: Integer);
    procedure OnListViewData(Sender: TObject; Item: TListItem);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

///////////////////////////////////////////////////////////////////////////////
/////   TForm1.AutoResizeColumn - auto-size column   //////////////////////////
///////////////////////////////////////////////////////////////////////////////

// AListView - list view object instance
// AColumn - index of the column to be auto-sized

procedure TForm1.AutoResizeColumn(const AListView: TListView;
  const AColumn: Integer);
var
  S: string;
  I: Integer;
  MaxWidth: Integer;
  ItemWidth: Integer;
begin
  // set the destination column width to the column's caption width
  // later on we'll check if we have a wider item
  MaxWidth := ListView_GetStringWidth(AListView.Handle,
    PChar(AListView.Columns.Items[AColumn].Caption));
  // iterate through all data items and check if their captions are
  // wider than the currently widest item if so then store that value
  for I := 0 to High(SampleArray) do
  begin
    case AColumn of
      0: S := SampleArray[I].Column1;
      1: S := SampleArray[I].Column2;
      2: S := SampleArray[I].Column3;
    end;
    ItemWidth := ListView_GetStringWidth(AListView.Handle, PChar(S));
    if MaxWidth < ItemWidth then
      MaxWidth := ItemWidth;
  end;
  // here is hard to say what value to use for padding to prevent the
  // string to be truncated; I've found the suggestions to use 6 px
  // for item caption padding and 12 px for subitem caption padding,
  // but a few quick tests confirmed me to use at least 7 px for items
  // and 14 px for subitems
  if AColumn = 0 then
    MaxWidth := MaxWidth + 7
  else
    MaxWidth := MaxWidth + 14;
  // and here we set the column width with caption padding included
  AListView.Columns.Items[AColumn].Width := MaxWidth;
end;

///////////////////////////////////////////////////////////////////////////////
/////   TForm1.FormCreate - setup the list view and fill custom data   ////////
///////////////////////////////////////////////////////////////////////////////

procedure TForm1.FormCreate(Sender: TObject);
var
  I: Integer;
begin
  ListView1.ViewStyle := vsReport;
  ListView1.Columns.Add.Caption := 'Column 1';
  ListView1.Columns.Add.Caption := 'Column 2';
  ListView1.Columns.Add.Caption := 'Column 3';
  ListView1.OwnerData := True;
  ListView1.OnData := OnListViewData;
  ListView1.Items.Count := High(SampleArray);

  for I := 0 to High(SampleArray) do
  begin
    SampleArray[I].Column1 := 'Cell [0, ' + IntToStr(I) + '] ' +
      DupeString('x', I);
    SampleArray[I].Column2 := 'Cell [1, ' + IntToStr(I) + '] ' +
      DupeString('x', High(SampleArray) - I);
    SampleArray[I].Column3 := '';
  end;
end;

///////////////////////////////////////////////////////////////////////////////
/////   TForm1.FormCreate - custom handler for OnData event   /////////////////
///////////////////////////////////////////////////////////////////////////////

procedure TForm1.OnListViewData(Sender: TObject; Item: TListItem);
begin
  Item.Caption := SampleArray[Item.Index].Column1;
  Item.SubItems.Add(SampleArray[Item.Index].Column2);
  Item.SubItems.Add(SampleArray[Item.Index].Column3);
end;

///////////////////////////////////////////////////////////////////////////////
/////   TForm1.Button1Click - auto-resize all 3 columns   /////////////////////
///////////////////////////////////////////////////////////////////////////////

procedure TForm1.Button1Click(Sender: TObject);
begin
  AutoResizeColumn(ListView1, 0);
  AutoResizeColumn(ListView1, 1);
  AutoResizeColumn(ListView1, 2);
end;

end.