Check .NET Version with Inno Setup

Inno Setup by Jordan Russell is a great installation scripting program, but lacks a built-in function to determine the .NET Framework version installed on the target machine. Fortunately, it’s easy to write such a function using Inno Setup’s Pascal scripting language.

Microsoft maintains a set of registry keys that indicate the installed .NET Framework versions and service packs. C# MVP Scott Dorman has posted the full list in this Stack Overflow thread. The required registry keys are quite similar for most .NET Framework versions except 1.0. We’ll ignore that version which has been obsoleted by 1.1 anyway.

In the following Inno Setup scripting code block, function IsDotNetDetected checks whether the specified .NET Framework version and at least the specified service pack level are installed. All listed version strings are for final release versions; betas and release candidates typically have different version numbers. Function InitializeSetup demonstrates how to use IsDotNetDetected to check for .NET Framework 4.0 Client Profile without service packs.

[Code]
function IsDotNetDetected(version: string; service: cardinal): boolean;
// Indicates whether the specified version and service pack of the .NET Framework is installed.
//
// version -- Specify one of these strings for the required .NET Framework version:
//    'v1.1.4322'     .NET Framework 1.1
//    'v2.0.50727'    .NET Framework 2.0
//    'v3.0'          .NET Framework 3.0
//    'v3.5'          .NET Framework 3.5
//    'v4\Client'     .NET Framework 4.0 Client Profile
//    'v4\Full'       .NET Framework 4.0 Full Installation
//
// service -- Specify any non-negative integer for the required service pack level:
//    0               No service packs required
//    1, 2, etc.      Service pack 1, 2, etc. required
var
    key: string;
    install, serviceCount: cardinal;
    success: boolean;
begin
    key := 'SOFTWARE\Microsoft\NET Framework Setup\NDP\' + version;
    // .NET 3.0 uses value InstallSuccess in subkey Setup
    if Pos('v3.0', version) = 1 then begin
        success := RegQueryDWordValue(HKLM, key + '\Setup', 'InstallSuccess', install);
    end else begin
        success := RegQueryDWordValue(HKLM, key, 'Install', install);
    end;
    // .NET 4.0 uses value Servicing instead of SP
    if Pos('v4', version) = 1 then begin
        success := success and RegQueryDWordValue(HKLM, key, 'Servicing', serviceCount);
    end else begin
        success := success and RegQueryDWordValue(HKLM, key, 'SP', serviceCount);
    end;
    result := success and (install = 1) and (serviceCount >= service);
end;

function InitializeSetup(): Boolean;
begin
    if not IsDotNetDetected('v4\Client', 0) then begin
        MsgBox('MyApp requires Microsoft .NET Framework 4.0 Client Profile.'#13#13
            'Please use Windows Update to install this version,'#13
            'and then re-run the MyApp setup program.', mbInformation, MB_OK);
        result := false;
    end else
        result := true;
end;