The reason is that the scroll bar contains child objects such as a track, a thumb and min and max buttons. It's these objects that respond to mouse events, not the parent object. So the solution is to set your mouse events to those objects. The problem is that those object are protected, so you'll have to create a new Scroll bar class that sets those events. The child objects don't yet exist in the TScrollBar constructor, so the best place to assign them I've found is on the first paint event.
I asked almost exactly the same question a couple of weeks ago. See my own answer here.
FMX: TScrollBar MouseDown and MouseUp events not triggering
Here's your example, which now works. I've also replaced your one label with 4 labels to make it easier to see which events get called.
New scroll bar class that does respond to mouse events:
unit ScrollBarMouse;
interface
uses
System.Classes, System.UITypes, FMX.StdCtrls, FMX.Types;
type
// A scroll bar that responds to mouse events
TScrollBarMouse = class(TScrollBar)
private
FMouseEventsSet : Boolean;
protected
procedure Paint; override;
public
constructor Create(AOwner: TComponent); override;
end;
implementation
constructor TScrollBarMouse.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FMouseEventsSet := False;
end;
procedure TScrollBarMouse.Paint;
begin
inherited;
// Track and Buttons are not assigned in constructor, so set mouse events on first paint
if not FMouseEventsSet and Assigned(Track) and Assigned(Track.Thumb)
and Assigned(MinButton) and Assigned(MaxButton) then begin
Track.OnMouseDown := OnMouseDown;
Track.OnMouseUp := OnMouseUp;
Track.OnMouseMove := OnMouseMove;
Track.Thumb.OnMouseDown := OnMouseDown;
Track.Thumb.OnMouseUp := OnMouseUp;
Track.Thumb.OnMouseMove := OnMouseMove;
MinButton.OnMouseDown := OnMouseDown;
MinButton.OnMouseUp := OnMouseUp;
MinButton.OnMouseMove := OnMouseMove;
MaxButton.OnMouseDown := OnMouseDown;
MaxButton.OnMouseUp := OnMouseUp;
MaxButton.OnMouseMove := OnMouseMove;
FMouseEventsSet := True;
end;
end;
end.
Form unit:
unit Unit1;
interface
uses
System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,
FMX.Controls.Presentation, FMX.StdCtrls, ScrollBarMouse;
type
TForm4 = class(TForm)
Label1: TLabel;
Label2: TLabel;
Label3: TLabel;
Label4: TLabel;
procedure ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Single);
procedure ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
procedure ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
procedure ScrollBar1Change(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
ScrollBar1 : TScrollBarMouse;
end;
var
Form4: TForm4;
implementation
{$R *.fmx}
procedure TForm4.FormCreate(Sender: TObject);
begin
// Create the scroll bar object
ScrollBar1 := TScrollBarMouse.Create(Self);
with ScrollBar1 do begin
Parent := Self;
Orientation := TOrientation.Vertical;
Position.X := 616;
Position.Y := 8;
Size.Width := 18;
Size.Height := 449;
OnMouseDown := ScrollBar1MouseDown;
OnMouseUp := ScrollBar1MouseUp;
OnMouseMove := ScrollBar1MouseMove;
OnChange := ScrollBar1Change;
end;
end;
procedure TForm4.ScrollBar1Change(Sender: TObject);
begin
Label1.Text := 'onChange: ' + IntToStr(Round(Screen.MousePos.Y));
end;
procedure TForm4.ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
begin
Label2.Text := 'mousedown: ' + IntToStr(Round(Y));
end;
procedure TForm4.ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Single);
begin
Label3.Text := 'mousemove: ' + IntToStr(Round(Y));
end;
procedure TForm4.ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
begin
Label4.Text := 'mouseUP: ' + IntToStr(Round(Y));
end;
end.
Form (scroll bar is removed since it's created at run time):
object Form4: TForm4
Left = 0
Top = 0
Caption = 'Form4'
ClientHeight = 480
ClientWidth = 640
FormFactor.Width = 320
FormFactor.Height = 480
FormFactor.Devices = [Desktop]
OnCreate = FormCreate
DesignerMasterStyle = 0
object Label1: TLabel
Position.X = 424.000000000000000000
Position.Y = 144.000000000000000000
Size.Width = 121.000000000000000000
Size.Height = 17.000000000000000000
Size.PlatformDefault = False
Text = 'Label1'
TabOrder = 3
end
object Label2: TLabel
Position.X = 424.000000000000000000
Position.Y = 168.000000000000000000
Size.Width = 121.000000000000000000
Size.Height = 17.000000000000000000
Size.PlatformDefault = False
Text = 'Label1'
TabOrder = 2
end
object Label3: TLabel
Position.X = 424.000000000000000000
Position.Y = 192.000000000000000000
Size.Width = 121.000000000000000000
Size.Height = 17.000000000000000000
Size.PlatformDefault = False
Text = 'Label1'
TabOrder = 1
end
object Label4: TLabel
Position.X = 424.000000000000000000
Position.Y = 216.000000000000000000
Size.Width = 121.000000000000000000
Size.Height = 17.000000000000000000
Size.PlatformDefault = False
Text = 'Label1'
TabOrder = 0
end
end
This was built using Delphi 10.4 and run in Windows 10.