MouseUp event handler does not detect the pressed mouse button
lazarus / 31-LCL

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simsee · 2023-11-20 14:30

As can be deduced from the following code, while the MouseDown event
handler detects the pressed mouse button and places it in the Shift
set, the same thing does not happen with MouseUp. Is this correct and
expected behavior?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs; type   { TForm1 }   TForm1 =
class(TForm)    procedure FormMouseDown(Sender: TObject; Button:
TMouseButton; Shift: TShiftState; X, Y: Integer);    procedure
FormMouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState;
X, Y: Integer);  private    procedure WriteShift(Shift: TShiftState); 
public   end; var  Form1: TForm1; implementation {$R *.lfm} { TForm1
} procedure TForm1.WriteShift(Shift: TShiftState);var  ShiftStateEnum
: TShiftStateEnum;begin  for ShiftStateEnum in TShiftStateEnum do   
if ShiftStateEnum in Shift then      writeln(ShiftStateEnum); 
writeln;end; procedure TForm1.FormMouseDown(Sender: TObject; Button:
TMouseButton; Shift: TShiftState; X, Y: Integer);begin 
writeln('FormMouseDown');  WriteShift(Shift);end; procedure
TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton; Shift:
TShiftState; X, Y: Integer);begin  writeln('FormMouseUp'); 
WriteShift(Shift);end; end.

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wp · 2023-11-20 14:45

This is the same as in Delphi. The logics behind it probably is: the
ShiftState represents the set of the pressed buttons. When the left
button is pressed it is included in the Shift set because it is down.
When it is released it is no longer held down and therefore removed
from Shift. But note: You can always get the button which is pressed
or released from the Button argument of the event handler.

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simsee · 2023-11-20 14:49

Thanks WP. So the State parameter in MouseUP carries no information
and is therefore useless.

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wp · 2023-11-20 14:57

No. You still can have the CTRL, SHIFT, ALT keys down... But yes, it
is useless regarding the mouse button.

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Josh · 2023-11-20 14:59

placing 2 labels on form, then using code below, the shift is detected
in mouse up and mousedown...


Code: [Select]procedure TForm1.FormMouseDown(Sender: TObject; Button:
TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
 if ssShift in Shift then label1.caption:='MD: Shift' else
label1.caption:='MD:';
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  If ssShift in Shift then label2.caption:='MU: Shift' else
label2.caption:='MU';
end;

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jamie · 2023-11-21 00:04

Works for me.

Hold the LEFT mouse button down and click the right mouse button.
The ssLEFT is reported, because that is the shift state.

Same the other way, hold the Right mouse button down and click the
left mouse button.

That reports ssRight mouse button.

So this means the buttons on the mouse that are being held down while
another mouse button is clicked reports the mouse button being held
down.

 If you want to know the actual clicked mouse button, use the BUTTON
parameter and from there, use a case statement to check the shift
states.

 Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Case Butotn
of  mbMiddle:If ssLeft in state Then... else if ssright in State then
...  
same for the ither mouse buttons.