[SOLVED] Disable CheckBox on TStringGrid
lazarus / 21-General

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pmesquita · 2021-03-11 14:12

Staff,

I have a TStringGrid with a cbsCheckboxColumn column but I need to
hide or disable the CheckBox on specific lines based on a check ... If
(AValue = 'Yes') The Disable or Hide;

Does anyone know how to proceed?
I've tried: 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 TCheckBox
(StringGrid1.Objects [0, 2]). Visible: = False; however gives access
violation

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wp · 2021-03-11 16:28

The checkboxes in stringgrids are not "real" checkboxes but "faked" to
display checkbox images.

I don't know how to hide the checkbox in some specific cells, but here
is a solution how to a make cells readonly:
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
TForm1.StringGrid1SelectCell(Sender: TObject; aCol, aRow: Integer; 
var CanSelect: Boolean);begin  if (ACol=1) and (ARow=1) then   
StringGrid1.Options := StringGrid1.Options - [goEditing]  else   
StringGrid1.Options := StringGrid1.Options + [goEditing];end;
Hmmm, not a very nice solution, because the disabled cell is not drawn
in some disabled style.

Another possibility is to provide customdrawn bitmaps. I took a
screenshot of a simple grid with checkboxes and used a graphics
program to cut out the checkbox images of the three states. These
images were saved as separate bmp files. Then I increased the
brightness of these images by a good fraction (75%) to mimic disabled
checkboxes - they were saved as well. Theses images were loaded into
my demo application (see attachment) at program start (and destroyed
at program end). Finally I wrote a handler for the
OnUserCheckboxBitmap event where I selected the bitmap according to
the Checkbox state provided as parameter.

BTW, when you include an empty bitmap you can also simulate a hidden
checkbox this way.

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pmesquita · 2021-03-11 17:38

Quote from: wp on March 11, 2021, 05:28:58 pmThe checkboxes in
stringgrids are not "real" checkboxes but "faked" to display checkbox
images.

I don't know how to hide the checkbox in some specific cells, but here
is a solution how to a make cells readonly:
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
TForm1.StringGrid1SelectCell(Sender: TObject; aCol, aRow: Integer; 
var CanSelect: Boolean);begin  if (ACol=1) and (ARow=1) then   
StringGrid1.Options := StringGrid1.Options - [goEditing]  else   
StringGrid1.Options := StringGrid1.Options + [goEditing];end;
Hmmm, not a very nice solution, because the disabled cell is not drawn
in some disabled style.

Another possibility is to provide customdrawn bitmaps. I took a
screenshot of a simple grid with checkboxes and used a graphics
program to cut out the checkbox images of the three states. These
images were saved as separate bmp files. Then I increased the
brightness of these images by a good fraction (75%) to mimic disabled
checkboxes - they were saved as well. Theses images were loaded into
my demo application (see attachment) at program start (and destroyed
at program end). Finally I wrote a handler for the
OnUserCheckboxBitmap event where I selected the bitmap according to
the Checkbox state provided as parameter.

BTW, when you include an empty bitmap you can also simulate a hidden
checkbox this way.


I didn't know that the CheckBoxes were just images.
So in this case, I can use the OnDrawCell event to draw a box
simulating that the CheckBox is hidden as in the example.

However I did not understand the reason that when running the
processor it is constantly 25%

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wp · 2021-03-11 23:17

Quote from: pmesquita on March 11, 2021, 06:38:05 pmHowever I did not
understand the reason that when running the processor it is constantly
25%
This is because you are writing to a cell during painting. When you
change a cell, the grid (or at least the changed cell) is repainted.
But when you do this during paint, another repaint is triggered which
triggers yet another repaint etc.

When you want to mark the cells with the invisible checkmarks by some
text such as 'Hide' as in your example you must do this outside the
painting cycle, for example when the grid is populated.

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pmesquita · 2021-03-12 13:16

Quote from: wp on March 12, 2021, 12:17:08 amQuote from: pmesquita on
March 11, 2021, 06:38:05 pmHowever I did not understand the reason
that when running the processor it is constantly 25%
This is because you are writing to a cell during painting. When you
change a cell, the grid (or at least the changed cell) is repainted.
But when you do this during paint, another repaint is triggered which
triggers yet another repaint etc.

When you want to mark the cells with the invisible checkmarks by some
text such as 'Hide' as in your example you must do this outside the
painting cycle, for example when the grid is populated.

I understand the reason ..
However I created the HideCheckBox procedure and after popularizing
the Grid I call the procedure but the CheckBox is still drawn instead
of putting the same code in OnDraw .. any suggestions?

I don't usually work with canvas so I'm kind of figuring out how it
works.


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
HideCheckBox(ACol, ARow: Integer);Var  LCellRect: TRect; Begin 
Form1.StringGrid1.Cells[ACol, aRow]:= 'Hide';  LCellRect:=
Form1.StringGrid1.CellRect(ACol, ARow); 
Form1.StringGrid1.Canvas.FillRect(LCellRect); End;

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wp · 2021-03-12 14:44

No, you must not paint in the HideCheckbox procedure because the OS
decides when painting will occur rather than you. You are only allowed
to paint within the related procedures (OnPaint, OnDrawCell, or
similar):

Remove the StringGrid.Canvas.FillRect from the procedure and replace
it by a StringGrid1.Invalidate -- this instructs the grid to repaint
itself at next occasion. (In fact, this is not even necessary because
the grid requests a repaint automatically whenever a cell changes).
Since you had marked the invisible cells by text 'Hide' you only must
make sure that this information is evaluated when repainting is done:

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
TForm1.StringGrid1DrawCell(Sender: TObject; aCol, aRow: Integer; 
aRect: TRect; aState: TGridDrawState);Var  LCellRect: TRect;begin  if
StringGrid1.Cells[ACol, ARow] = 'Hide') then  begin    LCellRect:=
StringGrid1.CellRect(ACol, ARow);   
StringGrid1.Canvas.FillRect(LCellRect);  end;end; 
A note on the HideCheckbox procedure: Why don't you make it a method
of TForm1? In this case it would work also when Form1 is named
differently:
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
TForm1.HideCheckBox(ACol, ARow: Integer);Var  LCellRect: TRect;begin 
StringGrid1.Cells[ACol, aRow]:= 'Hide';end;
Note: I did not test this code, there may be typos here and there...

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pmesquita · 2021-03-12 15:18

Quote from: wp on March 12, 2021, 03:44:47 pmNo, you must not paint in
the HideCheckbox procedure because the OS decides when painting will
occur rather than you. You are only allowed to paint within the
related procedures (OnPaint, OnDrawCell, or similar):

Remove the StringGrid.Canvas.FillRect from the procedure and replace
it by a StringGrid1.Invalidate -- this instructs the grid to repaint
itself at next occasion. (In fact, this is not even necessary because
the grid requests a repaint automatically whenever a cell changes).
Since you had marked the invisible cells by text 'Hide' you only must
make sure that this information is evaluated when repainting is done:

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
TForm1.StringGrid1DrawCell(Sender: TObject; aCol, aRow: Integer; 
aRect: TRect; aState: TGridDrawState);Var  LCellRect: TRect;begin  if
StringGrid1.Cells[ACol, ARow] = 'Hide') then  begin    LCellRect:=
StringGrid1.CellRect(ACol, ARow);   
StringGrid1.Canvas.FillRect(LCellRect);  end;end; 
A note on the HideCheckbox procedure: Why don't you make it a method
of TForm1? In this case it would work also when Form1 is named
differently:
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
TForm1.HideCheckBox(ACol, ARow: Integer);Var  LCellRect: TRect;begin 
StringGrid1.Cells[ACol, aRow]:= 'Hide';end;
Note: I did not test this code, there may be typos here and there...

Worked perfectly...
Now I understand, I didn't know that only in the events you mentioned
is allowed to work with the canvas .. good to know ...

Thank you very much for your help .. and long live Lazarus

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pmesquita · 2021-03-12 15:20

Quote from: wp on March 12, 2021, 03:44:47 pmA note on the
HideCheckbox procedure: Why don't you make it a method of TForm1? In
this case it would work also when Form1 is named differently:

I was too lazy to declare in the private of the form ...