Add additional controls to standard Inno Setup pages?

Question

How to add checkbox to the folder selection dialog created by the Inno Setup which is shown below in the image?

This is not a custom dialog. It is created by the Inno Setup automatically.

Answer 1

Set the Parent property of the checkbox to the WizardForm.SelectDirPage:

var
  Checkbox: TNewCheckBox;

procedure InitializeWizard();
begin
  Checkbox := TNewCheckBox.Create(WizardForm.SelectDirPage);
  Checkbox.Parent := WizardForm.SelectDirPage;
  Checkbox.Top := WizardForm.DirEdit.Top + WizardForm.DirEdit.Height + ScaleY(8);
  Checkbox.Left := WizardForm.DirEdit.Left;
  Checkbox.Caption := 'My checkbox';
  // See https://stackoverflow.com/q/30469660/850848
  Checkbox.Height := ScaleY(Checkbox.Height);
end;

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For finding the page names, see:
Inno Setup built-in control names

For placing controls on a custom page, see:
Placing image/control on Inno Setup custom page