Required a number in text box in Inno Setup

I found a code here that I needed. To only allow write numbers in a text box. But I still wanted more, which does not offer up the "Next" button without write the number in this text box.

Can help me?

procedure NumbersOnly(Sender: TObject; var Key: Char);
var
  S: string;
begin
  S := ('1234567890'#8);
  if Pos(Key, S) = 0 then 
    Key := #0;
end;

You can setup the next button to be enabled or disabled in the CurPageChanged event when the user reaches the page where your edit box resides. Except that you need to monitor changes of that edit box to enable or disable the next button according to whether there's something entered in that edit box. For this you need to write a handler for the OnChange event. Here is an example:

[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Code]
var
  MyEdit: TNewEdit;
  MyPage: TWizardPage;

procedure MyEditChange(Sender: TObject);
begin
  // enable the next button if the edit box is not empty; disable otherwise
  WizardForm.NextButton.Enabled := MyEdit.Text <> '';
end;

procedure MyEditKeyPress(Sender: TObject; var Key: Char);
var
  KeyCode: Integer;
begin
  // allow only numbers
  KeyCode := Ord(Key);
  if not ((KeyCode = 8) or ((KeyCode >= 48) and (KeyCode <= 57))) then
    Key := #0;
end;

procedure InitializeWizard;
begin
  MyPage := CreateCustomPage(wpWelcome, 'Caption', 'Description');

  MyEdit := TNewEdit.Create(WizardForm);
  MyEdit.Parent := MyPage.Surface;
  MyEdit.Left := 0;
  MyEdit.Top := 0;
  MyEdit.Width := 150;
  MyEdit.OnChange := @MyEditChange;
  MyEdit.OnKeyPress := @MyEditKeyPress;
end;

procedure CurPageChanged(CurPageID: Integer);
begin
  // if the currently turned wizard page is the one with the edit box, enable
  // the next button if the edit box is not empty; disable otherwise
  if CurPageID = MyPage.ID then
    WizardForm.NextButton.Enabled := MyEdit.Text <> '';
end;