Disabling deselect in TListView control

Question

I would like to use TListView (vsIcon) as a kind of tabs - so that only one item can be selected just like tabs. Selecting only one item is no problem (disabling Multiselect property). Problem is deselecting items when clicking on blank spots between icons and text in the listview.

Here is what I tried so far:

void __fastcall TForm::ListViewChanging(TObject *Sender, TListItem *Item, TItemChange Change, bool &AllowChange)
{
if (Change == ctState)
    {
    TPoint CursorRel = ListView->ScreenToClient(Mouse->CursorPos);
    AllowChange = (ListView->GetItemAt(CursorRel.x, CursorRel.y) != NULL);
    StatusBar->SimpleText = (AllowChange)? "YES" : "NO";
    }
}

The above works but there is a problem. When mouse is clicked on blank area it deselects the item and keyboard up/down arrow no longer work although the item still looks selected. If I ignore keyboard, for mouse selection it works fine and it ignores clicks on blank areas with the message "NO" in the statusbar.

Any ideas how to fix this so it works with all possible selection methods (keyboard, mouse (any other?)).

Answer 1

Here is another possible answer to your question :

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    ListView1: TListView;
    ImageList1: TImageList;
    StatusBar1: TStatusBar;
    procedure ListView1Changing(Sender: TObject; Item: TListItem;
      Change: TItemChange; var AllowChange: Boolean);
    procedure ListView1MouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure ListView1Enter(Sender: TObject);
  private
    FListItem: TListItem;
    procedure SelectedListItemStateSave;
    procedure SelectedListItemStateRestore;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.SelectedListItemStateRestore;
begin
  ListView1.Selected := FListItem;
  ListView1.Selected.Focused := True; // Always focused
end;

procedure TForm1.SelectedListItemStateSave;
begin
  FListItem := ListView1.Selected;
end;

procedure TForm1.ListView1Changing(Sender: TObject; Item: TListItem;
  Change: TItemChange; var AllowChange: Boolean);
begin
  if (Change=ctState) then
    SelectedListItemStateSave;
end;

procedure TForm1.ListView1Enter(Sender: TObject);
begin
  if ListView1.Selected = nil then
  begin
    FListItem :=ListView1.Items[0]; // Initialization
    SelectedListItemStateRestore;
  end;
end;

procedure TForm1.ListView1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if ListView1.GetItemAt(X,Y) = nil then
  begin
    SelectedListItemStateRestore;
  end;
end;

end.

Answer 2

Intercept WM_LBUTTONDOWN posted to the control and halt default processing if the click is not on an item. Subclass the control, or use an ApplicationEvents component, etc.. Delphi code sample with an interposer class:

type
  TListView = class(comctrls.TListView)
  protected
    procedure WMLButtonDown(var Message: TWMLButtonDown); message WM_LBUTTONDOWN;
  end;

  TForm1 = class(TForm)
    ListView1: TListView;
  private
    ..

procedure TListView.WMLButtonDown(var Message: TWMLButtonDown);
begin
  if GetItemAt(Message.XPos, Message.YPos) <> nil then
    inherited;
end;