TListViewで行の高さを低く設定したときの実際の高さを取得するには (ID:150579)

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うーむ，趣旨が理解し難いというか，何と言ったらいいのか．
以下のコードを試してみてください．
　　
　　
unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes,
  Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ComCtrls, Vcl.StdCtrls;

type
  TListView = class(Vcl.ComCtrls.TListView)
  private
    FItemHeight : UInt;
    procedure SetItemHeight(const Value: UInt);
  protected
    procedure CNMeasureitem(var Message: TWMMeasureItem); message CN_MEASUREITEM;
  public
    property ItemHeight : UInt read FItemHeight write SetItemHeight;
  end;

TForm1 = class(TForm)
    Button1: TButton;
    ListView1: TListView;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure ListView1DrawItem(Sender: TCustomListView; Item: TListItem;
      Rect: TRect; State: TOwnerDrawState);
  private
    { Private 宣言 }
  public
    { Public 宣言 }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

//=============================================================================
//  フォーム生成時の処理
//
//  本サンプルの動作確認は以下
//   Windows 10 ビルド 19043 Pro 64 bit + Delphi XE5(UP2) Pro VCL-32
//=============================================================================
procedure TForm1.FormCreate(Sender: TObject);
var
  LCol  : TListColumn;
  LItem : TListItem;
  LIndex: Integer;
begin
  ListView1.ViewStyle := vsReport;
  ListView1.OwnerDraw := True;
  ListView1.ItemHeight := 4;

ListView1.Items.BeginUpdate;
  LCol := ListView1.Columns.Add;
  LCol.Caption := 'Test Items';
  LCol.Width   := 200;

for LIndex := 0 to 49 do begin
    LItem :=  ListView1.Items.Add;
    LItem.Caption := Format('    %.6d',[LIndex + 1]);
  end;
  ListView1.Items.EndUpdate;
end;

//=============================================================================
//  ListView1 の行の高さを変更
//=============================================================================
procedure TForm1.Button1Click(Sender: TObject);
begin
  ListView1.ItemHeight := ListView1.ItemHeight + 2;
end;

//=============================================================================
//  ListView1 の OnDrawItem イベント
//=============================================================================
procedure TForm1.ListView1DrawItem(Sender: TCustomListView; Item: TListItem;
  Rect: TRect; State: TOwnerDrawState);
begin
  ListView1.Canvas.TextOut(Rect.Left, Rect.Top, Item.Caption);
end;

{ TListView }

//-----------------------------------------------     -------------------------
//  TListView の CN_MEASUREITEM メッセージ処理
//  CN_MEASUREITEM は，コントロール生成時に自身に送信されてくるメッセージ
//  ItemHeight の値を設定
//  OwnerDraw の値が True でないと機能しない　
//-----------------------------------------------     -------------------------
procedure TListView.CNMeasureitem(var Message: TWMMeasureItem);
begin
  inherited;
  Message.MeasureItemStruct.itemHeight := FItemHeight;
end;

//-----------------------------------------------     -------------------------
//  ItemHeight プロパティの設定用メソッド
//-----------------------------------------------     -------------------------
procedure TListView.SetItemHeight(const Value: UInt);
var
  LTopIndex : Integer;
begin
  if Value <> FItemHeight then begin
    FItemHeight := Value;

if Items.Count > 1 then begin
      LTopIndex := TopItem.Index;
      Selected := nil;
      RecreateWnd;
      Scroll(0, LTopIndex * FItemHeight);
    end;
  end;
end;

end.

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