Installing .NET Framework 4.7 automatically with Inno Setup

In this guide I will walk through how to get the .NET framework to download and install on-the-fly in an Inno Setup installer.

It works in 3 steps:

  1. Detect if the desired .NET framework is installed
  2. Download the .NET Framework bootstrap installer with Inno Download Plugin
  3. Run the bootstrap installer in quiet mode, which will download and install the .NET Framework. This is better than downloading the full installer since it only downloads the files it needs for your platform.

Here’s the full code:

#include <idp.iss>

// Other parts of installer file go here

IDP_DownloadFailed=Download of .NET Framework 4.7.2 failed. .NET Framework 4.7 is required to run VidCoder.
IDP_RetryCancel=Click 'Retry' to try downloading the files again, or click 'Cancel' to terminate setup.
InstallingDotNetFramework=Installing .NET Framework 4.7.2. This might take a few minutes...
DotNetFrameworkFailedToLaunch=Failed to launch .NET Framework Installer with error "%1". Please fix the error then run this installer again.
DotNetFrameworkFailed1602=.NET Framework installation was cancelled. This installation can continue, but be aware that this application may not run unless the .NET Framework installation is completed successfully.
DotNetFrameworkFailed1603=A fatal error occurred while installing the .NET Framework. Please fix the error, then run the installer again.
DotNetFrameworkFailed5100=Your computer does not meet the requirements of the .NET Framework. Please consult the documentation.
DotNetFrameworkFailedOther=The .NET Framework installer exited with an unexpected status code "%1". Please review any other messages shown by the installer to determine whether the installation completed successfully, and abort this installation and fix the problem if it did not.


  requiresRestart: boolean;

function NetFrameworkIsMissing(): Boolean;
  bSuccess: Boolean;
  regVersion: Cardinal;
  Result := True;

  bSuccess := RegQueryDWordValue(HKLM, 'Software\Microsoft\NET Framework Setup\NDP\v4\Full', 'Release', regVersion);
  if (True = bSuccess) and (regVersion >= 461308) then begin
    Result := False;

procedure InitializeWizard;
  if NetFrameworkIsMissing() then
    idpAddFile('', ExpandConstant('{tmp}\NetFrameworkInstaller.exe'));

function InstallFramework(): String;
  StatusText: string;
  ResultCode: Integer;
  StatusText := WizardForm.StatusLabel.Caption;
  WizardForm.StatusLabel.Caption := CustomMessage('InstallingDotNetFramework');
  WizardForm.ProgressGauge.Style := npbstMarquee;
    if not Exec(ExpandConstant('{tmp}\NetFrameworkInstaller.exe'), '/passive /norestart /showrmui /showfinalerror', '', SW_SHOW, ewWaitUntilTerminated, ResultCode) then
      Result := FmtMessage(CustomMessage('DotNetFrameworkFailedToLaunch'), [SysErrorMessage(resultCode)]);
      // See
      case resultCode of
        0: begin
          // Successful
        1602 : begin
          MsgBox(CustomMessage('DotNetFrameworkFailed1602'), mbInformation, MB_OK);
        1603: begin
          Result := CustomMessage('DotNetFrameworkFailed1603');
        1641: begin
          requiresRestart := True;
        3010: begin
          requiresRestart := True;
        5100: begin
          Result := CustomMessage('DotNetFrameworkFailed5100');
        else begin
          MsgBox(FmtMessage(CustomMessage('DotNetFrameworkFailedOther'), [IntToStr(resultCode)]), mbError, MB_OK);
    WizardForm.StatusLabel.Caption := StatusText;
    WizardForm.ProgressGauge.Style := npbstNormal;

function PrepareToInstall(var NeedsRestart: Boolean): String;
  // 'NeedsRestart' only has an effect if we return a non-empty string, thus aborting the installation.
  // If the installers indicate that they want a restart, this should be done at the end of installation.
  // Therefore we set the global 'restartRequired' if a restart is needed, and return this from NeedRestart()

  if NetFrameworkIsMissing() then
    Result := InstallFramework();

function NeedRestart(): Boolean;
  Result := requiresRestart;

Detecting if the desired .NET Framework is installed

First you need to determine what registry key to check to see if your .NET version is installed. There is a good Stack Overflow answer that covers this, though the Microsoft docs page is more likely to be up to date. There is also a good article on how to apply that in Inno Setup’s Pascal scripting language.

I wrote mine to check for .NET 4.7. (See the NetFrameworkIsMissing method)

Downloading the bootstrapper

Next we need to find out where to download the installer from. The .NET Framework Deployment Guide for Developers has a great list of stable download links for the bootstrapper (web) installers. I picked 4.7.2, as it still supports code targeting .NET 4.7, and we might as well give the users the latest we can. This link should prompt you to download an .exe file directly; if it’s bringing you to a download webpage, it won’t work.

Now install Inno Download Plugin. This will make the idpAddFile and idpDownloadAfter calls inside InitializeWizard work.

This “InitializeWizard” method is a special one that InnoSetup calls when first setting up its wizard pages. We call our helper function to detect if the framework is installed, then schedule a download step after the “Ready to install” page. We include our direct download link determined earlier, and save it in a temp folder, with a file name of “NetFrameworkInstaller.exe”. This name I picked arbitrarily; we just need to refer to it later when we’re installing and cleaning up.

Installing the bootstrapper

Our code is activated on PrepareToInstall. When this function returns a string, that string is shown as an error message that stops the install from happening. We call into InstallFramework and return its result.

Inside InstallFramework we’re running the bootstrapper we downloaded earlier, with a flag to make the install passive (non interactive). The /showrmui option prompts the user to close applications to avoid a system restart. /showfinalerror tells the installer to show an error message if the install fails. Our main installer will show this screen while the framework is getting downloaded and installed: 

Then the .NET installer UI will show alongside the first window:

If you’d like to keep it “cleaner” and just show the first screen you can swap out the /passive argument for /q. However I like showing the user the .NET install progress since it can take a long time and it reassures them that work is still really happening.

After running the installer, the bootstrapper is deleted (whether or not the install succeeded).

And now your installer is done!

Testing the installer

To test a .NET 4 or 4.7 install, I’d recommend setting up a Windows 7 virtual machine in Hyper-V. Windows 7 comes with .NET 2, 3 and 3.5 out of the box, but not .NET 4 or 4.7. After it installs the framework you can go to Programs and Features to cleanly remove it and test it all over again.

To test an earlier .NET version you should just be able to use a modern OS like Windows 8.1 or 10.

Thanks to Antony Male for suggesting updates to the error handling code.