{ 
  Question: 
  How do I capture a column resize event in TListView, the OnResize 
  only works when the ListView is changed? 

  Answer: 
  The event can be added with a bit of work. See the custom TListview derivative 
  below. It has 3 new events: 
  OnColumnResize, OnBeginColumnResize, OnEndColumnResize 
} 

unit PBExListview; 

interface 

uses 
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, 
  Dialogs, ComCtrls; 

type 
  TLVColumnResizeEvent = procedure(Sender: TCustomListview; 
    columnindex: Integer; 
    columnwidth: Integer) of object; 
  TPBExListview = class(TListview) 
  private 
    FBeginColumnResizeEvent: TLVColumnResizeEvent; 
    FEndColumnResizeEvent: TLVColumnResizeEvent; 
    FColumnResizeEvent: TLVColumnResizeEvent; 

  protected 
    procedure DoBeginColumnResize(columnindex, columnwidth: Integer); 
      virtual; 
    procedure DoEndColumnResize(columnindex, columnwidth: Integer); 
      virtual; 
    procedure DoColumnResize(columnindex, columnwidth: Integer); 
      virtual; 
    procedure WMNotify(var Msg: TWMNotify); message WM_NOTIFY; 
    function FindColumnIndex(pHeader: pNMHdr): Integer; 
    function FindColumnWidth(pHeader: pNMHdr): Integer; 
    procedure CreateWnd; override; 
  published 
    property OnBeginColumnResize: TLVColumnResizeEvent 
      read FBeginColumnResizeEvent write FBeginColumnResizeEvent; 
    property OnEndColumnResize: TLVColumnResizeEvent 
      read FEndColumnResizeEvent write FEndColumnResizeEvent; 
    property OnColumnResize: TLVColumnResizeEvent 
      read FColumnResizeEvent write FColumnResizeEvent; 
  end; 

procedure Register; 

implementation 

uses CommCtrl; 

procedure Register; 
begin 
  RegisterComponents('PBGoodies', [TPBExListview]); 
end; 

procedure TPBExListview.DoBeginColumnResize(columnindex, columnwidth: Integer); 
begin 
  if Assigned(FBeginColumnResizeEvent) then 
    FBeginColumnResizeEvent(Self, columnindex, columnwidth); 
end; 

procedure TPBExListview.DoEndColumnResize(columnindex, columnwidth: Integer); 
begin 
  if Assigned(FEndColumnResizeEvent) then 
    FEndColumnResizeEvent(Self, columnindex, columnwidth); 
end; 

procedure TPBExListview.DoColumnResize(columnindex, columnwidth: Integer); 
begin 
  if Assigned(FColumnResizeEvent) then 
    FColumnResizeEvent(Self, columnindex, columnwidth); 
end; 

function TPBExListview.FindColumnIndex(pHeader: pNMHdr): Integer; 
var 
  hwndHeader: HWND; 
  iteminfo: THdItem; 
  ItemIndex: Integer; 
  buf: array [0..128] of Char; 
begin 
  Result := -1; 
  hwndHeader := pHeader^.hwndFrom; 
  ItemIndex := pHDNotify(pHeader)^.Item; 
  FillChar(iteminfo, SizeOf(iteminfo), 0); 
  iteminfo.Mask := HDI_TEXT; 
  iteminfo.pszText := buf; 
  iteminfo.cchTextMax := SizeOf(buf) - 1; 
  Header_GetItem(hwndHeader, ItemIndex, iteminfo); 
  if CompareStr(Columns[ItemIndex].Caption, iteminfo.pszText) = 0 then 
    Result := ItemIndex 
  else 
  begin 
    for ItemIndex := 0 to Columns.Count - 1 do 
      if CompareStr(Columns[ItemIndex].Caption, iteminfo.pszText) = 0 then 
      begin 
        Result := ItemIndex; 
        Break; 
      end; 
  end; 
end; 

procedure TPBExListview.WMNotify(var Msg: TWMNotify); 
begin 
  inherited; 
  case Msg.NMHdr^.code of 
    HDN_ENDTRACK: 
      DoEndColumnResize(FindColumnIndex(Msg.NMHdr), 
        FindColumnWidth(Msg.NMHdr)); 
    HDN_BEGINTRACK: 
      DoBeginColumnResize(FindColumnIndex(Msg.NMHdr), 
        FindColumnWidth(Msg.NMHdr)); 
    HDN_TRACK: 
      DoColumnResize(FindColumnIndex(Msg.NMHdr), 
        FindColumnWidth(Msg.NMHdr)); 
  end; 
end; 

procedure TPBExListview.CreateWnd; 
var 
  wnd: HWND; 
begin 
  inherited; 
  wnd := GetWindow(Handle, GW_CHILD); 
  SetWindowLong(wnd, GWL_STYLE, 
    GetWindowLong(wnd, GWL_STYLE) and not HDS_FULLDRAG); 
end; 

function TPBExListview.FindColumnWidth(pHeader: pNMHdr): Integer; 
begin 
  Result := -1; 
  if Assigned(PHDNotify(pHeader)^.pItem) and 
    ((PHDNotify(pHeader)^.pItem^.mask and HDI_WIDTH) <> 0) then 
    Result := PHDNotify(pHeader)^.pItem^.cxy; 
end; 

end.