How do I install .NET Framework only when it's not already installed?

Question

Is there a way to check if the .NET Framework 4 has been installed and install it only when it's not in the system?

I know, how do I determine, if the .NET Framework 4 is installed by checking the following registry key?

hasDotnet4 :=
  RegKeyExists(HKEY_LOCAL_MACHINE, 'SOFTWARE\Microsoft\.NETFramework\policy\v4.0');

How do I conditionally run the .NET Framework 4 installation based on the above check?

Answer 1

The easiest you can do, is to use the Check parameter, which allows you to control if a certain file from the [Files] section will be extracted, or if a certain program from the [Run] section will be executed. The following script code shows its usage for the conditional installation of the .NET Framework 4:

[Files]
Source: "dotNetFx40_Full_setup.exe"; DestDir: {tmp}; \
  Flags: deleteafterinstall; Check: FrameworkIsNotInstalled

[Run]
Filename: "{tmp}\dotNetFx40_Full_setup.exe"; Check: FrameworkIsNotInstalled

[Code]

function FrameworkIsNotInstalled: Boolean;
begin
  Result :=
    not RegKeyExists(
      HKEY_LOCAL_MACHINE, 'SOFTWARE\Microsoft\.NETFramework\policy\v4.0');
end;