In Inno Setup choose a directory to install files from a pre-defined set

In this situation, I need to install a file to specific directory, but in different computer it might be in different folder so I need to check which on is correct.

For example, I have a file and it needs to install in A folder or B folder or C folder, depends on the computer has A or B or C. So I need to check them first, if the computer has B, then install the file in the B folder, etc.

I know I can use check after file's DestDir, if the directory doesn't exist then it won't install anything, but what I need is install that file to other directory.

Thanks in advance.

In the InitializeSetup event function, check for existence of your pre-defined set of directories and remember the one you find. Then set the default installation path to the found one using a scripted constant in the DefaultDirName directive.

You will possibly also want to set the DisableDirPage=yes and the UsePreviousAppDir=no.

[Setup]
DefaultDirName={code:GetDirName}
DisableDirPage=yes
UsePreviousAppDir=no

[Files]
Source: "MyProg.exe"; DestDir: "{app}"
Source: "MyProg.chm"; DestDir: "{app}"

[Code]

var
  DirName: string;

function TryPath(Path: string): Boolean;
begin
  Result := DirExists(Path);
  if Result then
  begin
    Log(Format('Path %s exists', [Path]))
    DirName := Path;
  end
    else
  begin
    Log(Format('Path %s does not', [Path]))
  end;
end;

function GetDirName(Param: string): string;
begin
  Result := DirName;
end;

function InitializeSetup(): Boolean;
begin
  Result :=
    TryPath('C:\path1') or
    TryPath('C:\path2') or
    TryPath('C:\path3');

  if Result then
  begin
    Log(Format('Destination %s selected', [DirName]))
  end
    else
  begin
    MsgBox('No destination found, aborting installation', mbError, MB_OK);
  end;
end;

Instead of using DefaultDirName={code:GetDirName}, you can also use DestDir: "{code:GetDirName}" in the respective entries of the [Files] section, if appropriate.