How do read and set the value of a checkbox in an InnoSetup wizard page?

Question

I have added a checkbox to the "Additional Tasks" page of an InnoSetup script with

[Tasks]
Name: "StartMenuEntry" ; Description: "Start my app when Windows starts" ; GroupDescription: "Windows Startup"; MinVersion: 4,4; 

I want to initialize this checkbox when the wpSelectTasks page shows, and read the value when the Next button is clicked. I can't work out how to access the checkbox `checked' value.

function NextButtonClick(CurPageID: Integer): Boolean;

var
  SelectTasksPage : TWizardPage ;
  StartupCheckbox : TCheckbox ;

begin
Result := true ;
case CurPageID of

    wpSelectTasks :
        begin
        SelectTasksPage := PageFromID (wpSelectTasks) ;
        StartupCheckbox := TCheckbox (SelectTasksPage... { <== what goes here??? }
        StartupCheckboxState := StartupCheckbox.Checked ;
        end ;
    end ;    
end ;     

Answer 1

The task check boxes are in fact items in the WizardForm.TasksList check list box. If you know their indexes you can access them pretty easily. Note, that the items can be grouped (what is just your case) and each new group takes also one item in that check list box, so for your case the item index will be 1:

[Setup]
AppName=TasksList
AppVersion=1.0
DefaultDirName={pf}\TasksList

[Tasks]
Name: "TaskEntry"; Description: "Description"; GroupDescription: "Group";

[code]
function NextButtonClick(CurPageID: Integer): Boolean;
begin
  Result := True;
  if CurPageID = wpSelectTasks then
  begin
    if WizardForm.TasksList.Checked[1] then
      MsgBox('First task has been checked.', mbInformation, MB_OK)
    else
      MsgBox('First task has NOT been checked.', mbInformation, MB_OK);
  end;
end;

procedure CurPageChanged(CurPageID: Integer);
begin
  if CurPageID = wpSelectTasks then
    WizardForm.TasksList.Checked[1] := False;
end;

Here is illustrated how the WizardForm.TasksList check list box would looks like when you'd have two tasks with different groups:

To access the task check box by its description try the following:

[Setup]
AppName=Task List
AppVersion=1.0
DefaultDirName={pf}\TasksList

[Tasks]
Name: "Task"; Description: "Task Description"; GroupDescription: "Group 1";

[code]
function NextButtonClick(CurPageID: Integer): Boolean;
var
  Index: Integer;
begin
  Result := True;
  if CurPageID = wpSelectTasks then
  begin
    Index := WizardForm.TasksList.Items.IndexOf('Task Description');
    if Index <> -1 then
    begin
      if WizardForm.TasksList.Checked[Index] then
        MsgBox('First task has been checked.', mbInformation, MB_OK)
      else
        MsgBox('First task has NOT been checked.', mbInformation, MB_OK);
    end;
  end;
end;

procedure CurPageChanged(CurPageID: Integer);
var
  Index: Integer;
begin
  if CurPageID = wpSelectTasks then
  begin
    Index := WizardForm.TasksList.Items.IndexOf('Task Description');
    if Index <> -1 then    
      WizardForm.TasksList.Checked[Index] := False;
  end;
end;   

Answer 2

Great answer above. Gave me just what I needed.

I had a case where I have a bunch of secondary installers that I used the 'checkonce' option on, but I wanted them to be re-checked if the folder was missing (e.g. the user wiped out the install folder manually), e.g.

[Tasks]
Name: "InstallPython" ; Description: "Install Python"     ; Flags: checkedonce
Name: "InstallNPP"    ; Description: "Install Notepad++"  ; Flags: checkedonce

[Code]
procedure CurPageChanged(CurPageID: Integer);
var
ItemIx: Integer;

begin
    if CurPageID = wpSelectTasks then begin
        if not DirExists(ExpandConstant('{app}')) then begin
            for ItemIx := 0 to (WizardForm.TasksList.Items.Count - 1) do
                WizardForm.TasksList.Checked[ItemIx] := True;
        end
    end
end;