How to detect a mouse click on a TListView Group header?

I'm using Delphi 10.1 and VCL. How can I detect a click or double-click on a Group header in a TListView? Not on a Column header.

Solution

The answer is based on Remy and Victoria comments, with an old answer by Bummi at https://www.entwickler-ecke.de/topic_ListViewEigenschaften+Delphi+vs+C+SubItems+auslesen_110307,0.html.

Few comments for the solution:

Subclass is an option but could be implemented with Form's ListView1MouseDown event too, which is a little bit simpler.
tLVHitTestInfo & LVM_HITTEST are defined in Winapi.CommCtrl.
```
Uses
  Winapi.CommCtrl; // For LVM_HITTEST
```
LVHT_EX_GROUP_HEADER value should be defined manually. I didn't find it inside any Delphi unit. It is the identifier that a Group header was clicked. It should be verified with LVHitTestInfo.flags. It is Valid for Windows Vista and above.
```
const
  LVHT_EX_GROUP_HEADER = $10000000;
```
LVHitTestInfo.iGroup Doesn't work! I don't know the reason. Originally, I thought it should be the Group index.

The example has a form with ListView on it, the style is ViewStyle = vsReport. A mouse click on a group header will invoke a message dialog with the group index. Here is the detailed code:

    Uses Winapi.CommCtrl;

    procedure TForm1.ListView1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    const
      LVHT_EX_GROUP_HEADER = $10000000; // It is Valid for Windows Vista and above.
    var
      HTI: tLVHitTestInfo; // Defined on Winapi.CommCtrl
      nGroupInx: integer;
    begin
      HTI.pt     := point(X, Y); // Add cursor position
      nGroupInx  := SendMessage(ListView1.Handle, LVM_HITTEST, -1, LPARAM(@HTI)); // Return an Item
      if nGroupInx <> -1 then // Is an Item found?
        if (HTI.flags and LVHT_EX_GROUP_HEADER) = LVHT_EX_GROUP_HEADER then // Is it a Group Header?
            ShowMessage('Clicked Group header:' + ' ' + nGroupInx.ToString);
    end;