如何在VCL样式的应用程序中居中设置TListView标题标题？

Question

我有一个列表视图控件（ListView这里），我用这样的代码填充它：

var
  Item: TListItem;
  Column: TListColumn;
begin    
  ListView.ViewStyle := vsReport;

  Column := ListView.Columns.Add;
  Column.Width := 200;
  Column.Alignment:= taCenter;
  Column.Caption:= 'Column 1';

  Column:= ListView.Columns.Add;
  Column.Width := 200;
  Column.Alignment := taCenter;
  Column.Caption := 'Column 2';

  Item := ListView.Items.Add;
  Item.Caption := 'Item 1';
  Item.SubItems.Add('Subitem 1');
end;

问题是当我在我的应用程序中使用VCL样式时，文本不在列表视图标题中居中：

如何将标题标题置于VCL样式的应用程序中心？

Answer 1

负责绘制列标题的样式挂钩永远不会检查列的文本对齐方式，并且总是以左对齐方式绘制文本，显然是疏忽。

首先为祖先创建Vcl.ComCtrls.TListViewStyleHook的后代和一个类助手，以便我们可以访问我们需要的私有变量。

TListViewStyleHookHelper = class helper for TListViewStyleHook
    function getFHeaderHandle: HWnd;
  end;

TListViewStyleHookEx = class(Vcl.ComCtrls.TListViewStyleHook)
  strict protected
    procedure DrawHeaderSection(Canvas: TCanvas; R: TRect; Index: Integer;
      const Text: string; IsPressed, IsBackground: Boolean); override;
  end;

修复方法：

uses
  Winapi.Commctrl;


function TListViewStyleHookHelper.getFHeaderHandle: HWnd;
begin
  Result := Self.FHeaderHandle;
end;


procedure TListViewStyleHookEx.DrawHeaderSection(Canvas: TCanvas; R: TRect;
  Index: Integer; const Text: string; IsPressed, IsBackground: Boolean);
var
  Item: THDItem;
  ImageList: HIMAGELIST;
  DrawState: TThemedHeader;
  IconWidth, IconHeight: Integer;
  Details: TThemedElementDetails;
  LListView: TListView;
  DT_Align: Integer;
begin
  FillChar(Item, SizeOf(Item), 0);
  Item.mask := HDI_FORMAT;
  Header_GetItem(getFHeaderHandle, Index, Item);
  if IsBackground then
    DrawState := thHeaderItemNormal
  else if IsPressed then
    DrawState := thHeaderItemPressed
  else
    DrawState := thHeaderItemNormal;

  Details := StyleServices.GetElementDetails(DrawState);
  StyleServices.DrawElement(Canvas.Handle, Details, R);

  ImageList := SendMessage(getFHeaderHandle, HDM_GETIMAGELIST, 0, 0);
  Item.mask := HDI_FORMAT or HDI_IMAGE;
  InflateRect(R, -2, -2);
  IconWidth := 0;
  if (ImageList <> 0) and Header_GetItem(getFHeaderHandle, Index, Item) then
  begin
    if Item.fmt and HDF_IMAGE = HDF_IMAGE then
    begin
      ImageList_Draw(ImageList, Item.iImage, Canvas.Handle, R.Left, R.Top,
        ILD_TRANSPARENT);
      ImageList_GetIconSize(ImageList, IconWidth, IconHeight);
      Inc(R.Left, IconWidth + 5);
    end;
  end;
  if IconWidth = 0 then
    Inc(R.Left, 2);

  DT_Align := 0;

  if Control is TListView then
  begin
    LListView := TListView(Control);
      if (Index > -1) and (Index < LListView.Columns.Count) then
        case LListView.Columns[Index].Alignment of
          taLeftJustify:
            DT_Align := 0;
          taRightJustify:
            DT_Align := 2;
          taCenter:
            DT_Align := 1;
        end;
  end;

  DrawControlText(Canvas, Details, Text, R, DT_VCENTER or DT_Align or
    DT_SINGLELINE or DT_END_ELLIPSIS);

end;

最后我们必须为TListView控件注册我们的扩展样式钩子：

Initialization
 TCustomStyleEngine.RegisterStyleHook(TListView, TListViewStyleHookEx);

Finalization
 TCustomStyleEngine.UnRegisterStyleHook(TListView, TListViewStyleHookEx);