TDateTimePicker: Setting Min and Max Date
lazarus / 31-LCL

----------------------------------------------------------------------
Jvan · 2021-05-07 23:31

This is my code:

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 procedure
TfrmMain._MinMaxFechaContable();var  anho, mes: Integer;  myDtp:
TDateTimePicker;begin  anho := 2000 + cmbPerContAnho.ItemIndex;  mes
:= cmbPerContMes.ItemIndex;  myDtp := frmAstCont.dtpAstFchCont;  if
(mes = 0) then begin    //El 1er día del mes seleccionado:   
myDtp.MinDate := EncodeDate(anho, 1, 1);    //El 31 de diciembre del
año seleccionado:    myDtp.MaxDate := EncodeDate(anho, 12, 31);  end
else begin    //El 1er día del mes seleccionado:    myDtp.MinDate :=
EncodeDate(anho, mes, 1);    //El mes siguiente menos 1 día:   
myDtp.MaxDate := IncMonth(myDtp.MinDate, 1) - 1.0;  end; end; 
But I had this error showed in "error1.png".

----------------------------------------------------------------------
lucamar · 2021-05-07 23:53

Does frmAstCont (which I assume is a form) exist and does it contain a
(TDateTimePicker?) dtpAstFchCont control?

----------------------------------------------------------------------
speter · 2021-05-08 00:07

In addition to lucamar's comments, do "cmbPerContAnho" and
"cmbPerContMes" exist (have they been created)!?

cheers
S.

----------------------------------------------------------------------
Jvan · 2021-05-08 14:05

Yes, they exist. I can see them, so they exist.

"cmbPerContAnho" and "cmbPerContMes" are on the main form. And
"dtpAstFchCont" in on a ShowModal form.

----------------------------------------------------------------------
wp · 2021-05-08 14:29

Maybe the form frmAstCont does not yet exist when your code is called?
Is it in the list of auto-created forms (in the project options)? Or
do you create it at run-time? Maybe you forgot to create it? It's hard
to tell without seeing all of your code...

In general: Put a breakpoint into the procedure which raises the
exception. When the program stops open "View" > "Debug windows" >
"call stack" -- this shows you from which routine the breakpoint
procedure is called, and the routine from which this other routine is
called etc. Study these lines and check whether the form already
exists when they are called.

----------------------------------------------------------------------
Jvan · 2021-05-08 16:21

I created a new project with my code. I had the same problem.

----------------------------------------------------------------------
wp · 2021-05-08 17:00

As lucamar and I told you...

You access frmAstCont in the OnCreate event of Form1. Looking at the
project file you will see that at this time the frmAstCont is not yet
created and thus nil.

You can use the OnShow or OnActivate events instead. On the other
hand, these events may be fired later during execution of the program
again. To prevent unwanted side-effects when this happens, I often
implement a method "BeforeRun" of the mainform which is called in the
project unit immediately before Application.Run.
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 type 
TForm1 = class(TForm)  ...  public    procedure BeforeRun;    ... 
end; procedure TForm1.BeforeRun;begin  _MinMaxFechaContable;
end; ---------- program Project;...begin  .... 
Application.Initialize;  Application.CreateForm(TForm1, Form1); 
Application.CreateForm(TfrmAstCont, frmAstCont);  Form1.BeforeRun; 
Application.Run;end. 
This way the crash due to nonexisting frmAstConCont is prevented. But
as you'll notice there is another problem with your comboboxes - I'll
leave this to you to find a solution...

----------------------------------------------------------------------
Jvan · 2021-05-08 19:19

Thanks.