Inno Setup Detect changed task/item in TasksList.OnClickCheck event - inno-setup

Question

I'm stuck on simple situation with OnClickCheck property. The problem is that I see a Msgbox every time I turn on backup task, but also (while it's switched on) OnClickCheckappeared on pressing uninst task too! Seems that OnClickCheck checks all clicks, but I need to check click only on the first task.
It is logical to add to "WizardForm.TasksList.OnClickCheck" exact number of task (WizardForm.TasksList.OnClickCheck[0]), but compiler doesn't agree with it.
[Tasks]
Name: backup; Description: do backup
Name: uninst; Description: do not create uninstaller
[Code]
procedure TaskOnClick(Sender: TObject);
begin
if IsTaskSelected('backup') then
begin
MsgBox('backup task has been checked.', mbInformation, MB_OK)
end;
end;
procedure InitializeWizard();
begin
WizardForm.TasksList.OnClickCheck := #TaskOnClick;
end;

Answer 1

There's no way tell exactly what task (list item) was changed in the OnClickCheck event.
To tell which item was checked by the user, you can use the ItemIndex property. The user can check only the selected item.
Though if you have a task hierarchy, even unselected task can be toggled automatically by the installer due to a change in child/parent items. So to tell all changes, all you can do is to remember the previous state and compare it against the current state, when the OnClickCheck is called.
var
TasksState: array of TCheckBoxState;
procedure TasksClickCheck(Sender: TObject);
var
I: Integer;
begin
for I := 0 to WizardForm.TasksList.Items.Count - 1 do
begin
if TasksState[I] <> WizardForm.TasksList.State[I] then
begin
Log(Format('Task %d state changed from %d to %d',
[I, TasksState[I], WizardForm.TasksList.State[I]]));
TasksState[I] := WizardForm.TasksList.State[I];
end;
end;
end;
procedure CurPageChanged(CurPageID: Integer);
var
I: Integer;
begin
if CurPageID = wpSelectTasks then
begin
{ Only now is the task list initialized (e.g. based on selected setup }
{ type and components). Remember what is the current/initial state. }
SetArrayLength(TasksState, WizardForm.TasksList.Items.Count);
for I := 0 to WizardForm.TasksList.Items.Count - 1 do
TasksState[I] := WizardForm.TasksList.State[I];
end;
end;
procedure InitializeWizard();
begin
WizardForm.TasksList.OnClickCheck := #TasksClickCheck;
end;
Instead of using indexes, you can also use task names with use of WizardSelectedTasks or WizardIsTaskSelected. For an example, see Inno Setup: how to auto select a component if another component is selected?
Also see:
Inno Setup ComponentsList OnClick event
Inno Setup Uncheck a task when another task is checked
Inno Setup - Show children component as sibling and show check instead of square in checkbox