How to show progress during "PrepareToInstall"? - inno-setup

Question

An installer I'm working on does most of its work in the PrepareToInstall function, as everything I need to do might fail, and therefore this is the appropriate place to handle these things in case they do fail. Any failure can be automatically reported by passing the error message in the function's result. There are only 3 small files which the installer actually copies over.
The problem is that the wizard seems to freeze (or not respond rather) during this function, just showing a blank page titled "Preparing to install..." while in reality, it's going through my install process.
I would like to show the progress to the user with a simple procedure ShowProgress(const S: String); which shows the user what it's actually doing. How can I do this?
This is how I'm doing my install, where I'd like to wrap each call to Log()...
function PrepareToInstall(var NeedsRestart: Boolean): String;
var
R: Integer;
begin
Result:= '';
try
Log('Doing this...');
R:= DoThis;
case R of
0: begin
Result:= '';
end;
1: begin
Result:= 'Error message 1 was raised while doing this.';
end;
else begin
Result:= 'Unexpected error doing this: ' + IntToStr(R);
end;
end;
if Result = '' then begin
Log ('Doing that...');
R:= DoThat;
case R of
0: begin
Result:= '';
end;
1: begin
Result:= 'Error message 1 was raised while doing that.';
end;
else begin
Result:= 'Unexpected error doing that: ' + IntToStr(R);
end;
end;
end;
if Result = '' then begin
Log ('Doing something else...');
R:= DoSomethingElse;
case R of
0: begin
Result:= '';
end;
1: begin
Result:= 'Error message 1 was raised while doing something else.';
end;
else begin
Result:= 'Unexpected error doing something else: ' + IntToStr(R);
end;
end;
end;
//A few more blocks like above
//Error logging
if Result <> '' then begin
Log('FAILURE: '+Result);
end;
except
Result:= 'EXCEPTION';
Log('EXCEPTION');
end;
end;

Answer 1

I mixed all your answers guys and I found another possible solution to this question.
I know this is not a so called 'elegant solution'.
Anyway it is a quick solution that can avoid you to develop a separated DLL with custom controls managing the communication between the installer and the DLL.
The following approach describe how to create a custom Page that is a copy of the Page Inno Setup shows during PrepareToInstall setup phase.
This copy must have the same look and feel of the original one plus a progress bar and a label that developer can use to indicate the current step of the PrepareToInstall setup phase.
Let's see some code.
First of all, prepare the custom Page:
[Code]
var
PrepareToInstallWithProgressPage : TOutputProgressWizardPage;
Now define PrepareToInstall function to add our custom stuff:
function PrepareToInstall(var NeedsRestart: Boolean): String;
var
ResultCode: Integer;
begin
PrepareToInstallWithProgressPage.SetProgress(0, 0);
PrepareToInstallWithProgressPage.Show;
try
// First preinstallation step: suppose to kill currently app you are going to update
PrepareToInstallWithProgressPage.SetText('Exiting MyApp Running Instances'), '');
ExecuteCmd('taskkill', '/F /IM MyApp');
// Set progress bar to 10%
PrepareToInstallWithProgressPage.SetProgress(1, 10);
// Second preinstallation step
// DoSomething usefull...
// Set progress bar to 20% after done
PrepareToInstallWithProgressPage.SetProgress(2, 10);
// ...do other preinstallation steps till the end
PrepareToInstallWithProgressPage.SetProgress(10, 10);
finally
PrepareToInstallWithProgressPage.Hide;
end;
end;
At this installation phase we completed the steps for prepare to install phase so the default PrepareToInstall Page of Inno Setup is shown for a while.
Now, the user probably cannot understand that the page changes because our PrepareToInstallWithProgressPage has the same look and feel of the original one.
In order to let our page has the same look and feel we can use SetupMessage function to get the 2 strings of the original Inno Setup PrepareToInstall page.
Using SetupMessage we can avoid to duplicate and localize strings for our custom page to copy the originals.
Just like this:
procedure InitializeWizard;
var
A: AnsiString;
S: String;
begin
// The string msgWizardPreparing has the macro '[name]' inside that I have to replace with the name of my app, stored in a define constant of my script.
S := SetupMessage(msgPreparingDesc);
StringChange(S, '[name]', '{#MY_APPNAME}');
A := S;
PrepareToInstallWithProgressPage := CreateOutputProgressPage(SetupMessage(msgWizardPreparing), A);
end;
I hope this help.

Answer 2

Have a look at the CodeDlg.iss example script included with Inno, in particular at the code that uses CreateOutputProgressPage.
This page type allows you to show a status message and/or a progress bar while you are performing other actions. And it automatically pumps messages whenever you change the progress label/value to ensure that the user sees the correct status.
It is intended for precisely this kind of code.

Answer 3

The code written in the PrepareToInstall function blocks the Windows message pump from processing, rendering the wizard form non-responsive. If many controls are needed to be visible in this screen, showing perhaps a progress bar and list of steps to take, this can be done with a form inside of a DLL. Make sure there is a thread in this DLL which does the actual install process, and only update the GUI to display the status to the user. This DLL form may overlay the wizard, or may even be embedded inside of the wizard in a custom wizard page, for example. The idea is to move your install code from the PrepareToInstall function to within this thread, and only then will you be able to achieve a fully responsive GUI during this process. From the PrepareToInstall function, there should be just one DLL call to initiate the install process, which in turn shows the form from the DLL.
The result may look something like this (in the works):