Show custom control hint when disabled - delphi

Question

I've written a custom control (TCustomControl) which shows the standard built-in hint on hovering. However, when the control is disabled, the hint does not show. But, the TSpeedButton does show a hint when it's disabled, so there must be a way I can do the same in my control.
What do I need to do to show hints when my control is disabled?

Answer 1

The standard hint mechanism is based on mouse messages. Controls derived from TWinControl (which includes TCustomControl) do not receive mouse messages when disabled, and the hint system internally ignores disabled windowed controls. TSpeedButton is derived from TGraphicControl instead of TWinControl, so it is not subject to those restrictions.

Answer 2

You need to enable the window handle in order to get a WM_MOUSEMOVE which starts showing the hint. This has some implications.
First, to enable the window handle (WinAPI), you need to delete the WS_DISABLED style from the window style, or use EnableWindow. This modification does not synchronize the VCL's Enabled property (unlike the other way around: setting the Enabled property dóes call EnableWindow), which is why this works.
But enabling the window handle lets all mouse messages through, so you have to block them and activate the hint manually on WM_MOUSEMOVE:
type
TMyControl = class(TCustomControl)
private
FDisabledHint: Boolean;
procedure CheckEnabled;
procedure SetDisabledHint(Value: Boolean);
procedure CMEnabledchanged(var Message: TMessage);
message CM_ENABLEDCHANGED;
protected
procedure CreateParams(var Params: TCreateParams); override;
procedure SetParent(AParent: TWinControl); override;
procedure WndProc(var Message: TMessage); override;
published
property DisabledHint: Boolean read FDisabledHint write SetDisabledHint;
end;
{ TMyControl }
procedure TMyControl.CheckEnabled;
begin
if DisabledHint and HasParent and (not Enabled) and
not (csDesigning in ComponentState) then
EnableWindow(Handle, True);
end;
procedure TMyControl.CMEnabledchanged(var Message: TMessage);
begin
inherited;
CheckEnabled;
end;
procedure TMyControl.CreateParams(var Params: TCreateParams);
begin
inherited CreateParams(Params);
if DisabledHint and not Enabled then
Params.Style := Params.Style and (not WS_DISABLED);
end;
procedure TMyControl.SetDisabledHint(Value: Boolean);
begin
if FDisabledHint <> Value then
begin
FDisabledHint := Value;
CheckEnabled;
end;
end;
procedure TMyControl.SetParent(AParent: TWinControl);
begin
inherited SetParent(AParent);
CheckEnabled;
end;
procedure TMyControl.WndProc(var Message: TMessage);
begin
if not Enabled and DisabledHint and (Message.Msg = WM_MOUSEMOVE) then
Application.HintMouseMessage(Self, Message);
if Enabled or (Message.Msg < WM_MOUSEFIRST) or
(Message.Msg > WM_MOUSELAST) then
inherited WndProc(Message);
end;
I checked the working of the TabStop property, and this solution does not interfere with it. But beware of issues which I have not thought of yet.
(Besides, why a disabled TControl shows a hint is because it receives a CM_MOUSEENTER from WndProc of its parent, despite of that same parent blocking all other mouse input via IsControlMouseMsg to prevent the mouse events from firing.)

Answer 3

Actually you control's Winproc doesn't even get called when you control is disabled. Thy this small demo in order for understainding the message loop a bit better.
Place a TPanel on a form, and add a Double clickEvent To the form. Then try this code:
unit Unit39;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls;
type
TPanel = class(ExtCtrls.TPanel)
protected
procedure WndProc(var Message: TMessage); override;
end;
TForm39 = class(TForm)
Panel1: TPanel;
procedure FormDblClick(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form39: TForm39;
implementation
{$R *.dfm}
{ TPanel }
procedure TPanel.WndProc(var Message: TMessage);
begin
inherited;
Application.MainForm.Caption := FloatToStr(now);
end;
procedure TForm39.FormDblClick(Sender: TObject);
begin
Panel1.Enabled := not Panel1.Enabled;
end;
end.
YES! Correct: Ugly hack and violation of ALL designpatterns but with this small example you can see how the message loop works, and it is a very simple way to test some thing.
PS: I placed this as an answer because you can not format you text in comment :D