How to disable NextButton when file is not selected on InputFilePage (CreateInputFilePage)? - inno-setup

Question

My Inno Setup program have a custom "input file page" that was created using CreateInputFilePage.
How can I disable the NextButton in this page until the file path is properly picked by the user?
In other words, I need to make the NextButton unclickable while the file selection form is empty, and clickable when the file selection form is filled.
Thank you.

Answer 1

The easiest way is to use NextButtonClick to validate the inputs and display an error message when the validation fails.
var
FilePage: TInputFileWizardPage;
procedure InitializeWizard();
begin
FilePage := CreateInputFilePage(wpSelectDir, 'caption', 'description', 'sub caption');
FilePage.Add('prompt', '*.*', '.dat');
end;
function NextButtonClick(CurPageID: Integer): Boolean;
begin
Result := True;
if (CurPageID = FilePage.ID) and
(Length(FilePage.Edits[0].Text) = 0) then
begin
MsgBox('Please select a file.', mbError, MB_OK);
WizardForm.ActiveControl := FilePage.Edits[0];
Result := False;
end;
end;
If you really want to update the "Next" button state while the input changes, it is a bit more complicated:
procedure FilePageEditChange(Sender: TObject);
begin
WizardForm.NextButton.Enabled := (Length(TEdit(Sender).Text) > 0);
end;
procedure FilePageActivate(Sender: TWizardPage);
begin
FilePageEditChange(TInputFileWizardPage(Sender).Edits[0]);
end;
procedure InitializeWizard();
var
Page: TInputFileWizardPage;
Edit: TEdit;
begin
Page := CreateInputFilePage(wpSelectDir, 'caption', 'description', 'sub caption');
{ To update the Next button state when the page is entered }
Page.OnActivate := #FilePageActivate;
Edit := Page.Edits[Page.Add('prompt', '*.*', '.dat')];
{ To update the Next button state when the edit contents changes }
Edit.OnChange := #FilePageEditChange;
end;