How to adjust hint properties of a control at runtime? - delphi

Question

I have this code with which I can set the font size of the control hint, but I want to be able somehow to adjust it later at runtime. How can I do that ?
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TMyHintWindow = class(THintWindow)
constructor Create(AOwner: TComponent); override;
end;
TMyButton = class(TButton)
protected
procedure CMHintShow(var Message: TCMHintShow); message CM_HINTSHOW;
end;
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
MyButton: TMyButton;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
MyButton:=TMyButton.Create(Form1);
MyButton.Parent:=Form1;
MyButton.Caption:='Test';
MyButton.Left:=100;
MyButton.Top:=100;
MyButton.ShowHint:=true;
end;
procedure TMyButton.CMHintShow(var Message: TCMHintShow);
begin
inherited;
Message.HintInfo.HintWindowClass:=TMyHintWindow;
Message.HintInfo.HintStr:='My custom hint';
end;
constructor TMyHintWindow.Create(AOwner: TComponent);
begin
inherited;
Canvas.Font.Size:=25;
end;
end.

Answer 1

Since there is only one hint window instance at the time, and that instance will be created after call to CMHintShow, you can use class variables to do additional hint customization. Class variable is class member that is shared among all instances of the class and can be accessed directly through class type or class instance.
type
TMyHintWindow = class(THintWindow)
protected
class constructor ClassCreate;
public
class var FontSize: integer;
constructor Create(AOwner: TComponent); override;
end;
class constructor TMyHintWindow.ClassCreate;
begin
FontSize := 25;
end;
constructor TMyHintWindow.Create(AOwner: TComponent);
begin
inherited;
Canvas.Font.Size := FontSize;
end;
and then you can change FontSize in CMHintShow method
procedure TMyButton.CMHintShow(var Message: TCMHintShow);
begin
inherited;
TMyHintWindow.FontSize := 12;
Message.HintInfo.HintWindowClass := TMyHintWindow;
Message.HintInfo.HintStr := 'My custom hint';
end;

Answer 2

Starting from indications given by TLama I finally solved this problem. The key was to set Canvas.Font.Size in TMyHintWindow.CalcHintRect.
Here is the code:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TMyHintData = record
FontSize: Integer;
end;
TMyHintWindow = class(THintWindow)
public
function CalcHintRect(MaxWidth: Integer; const AHint: string; AData: TCustomData): TRect; override;
end;
TMyButton = class(TButton)
private
procedure CMHintShow(var AMessage: TCMHintShow); message CM_HINTSHOW;
public
FMyHintData: TMyHintData;
constructor Create(AOwner: TComponent); override;
end;
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
MyButton: TMyButton;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
TMyButton(Sender).FMyHintData.FontSize:=44;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
MyButton:=TMyButton.Create(Form1);
MyButton.Parent:=Form1;
MyButton.Caption:='Test';
MyButton.Left:=100;
MyButton.Top:=100;
MyButton.ShowHint:=true;
MyButton.OnClick:=Button1Click;
end;
function TMyHintWindow.CalcHintRect(MaxWidth: Integer; const AHint: string; AData: TCustomData): TRect;
begin
Canvas.Font.Size:=TMyHintData(AData^).FontSize;
Result:=inherited;
end;
constructor TMyButton.Create(AOwner: TComponent);
begin
inherited;
FMyHintData.FontSize:=25;
end;
procedure TMyButton.CMHintShow(var AMessage: TCMHintShow);
begin
inherited;
AMessage.HintInfo.HintData:=#FMyHintData;
AMessage.HintInfo.HintWindowClass:=TMyHintWindow;
AMessage.HintInfo.HintStr:='My custom hint';
end;
end.

Answer 3

procedure TForm1.FormCreate(Sender: TObject);
begin
Application.OnShowHint:=AppOnShowHint;
end;
procedure TForm1.AppOnShowHint(var HintStr: string; var CanShow: Boolean; var HintInfo: THintInfo);
begin
{Use HintInfo (type:THintInfo) to specify some property of hint-window}
{For example: set hint-window width to the width of longest word in the hint-text}
HintInfo.HintMaxWidth:=1;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
{Set HintFont at runtime}
Screen.HintFont.Size:=strtoint(Edit1.Text);
{It's necessary to recreate the Application.FHintWindow private variable, so:}
Application.ShowHint:=False;
Application.ShowHint:=True;
end;