有没有一种方法来检查.NET Framework 4中已安装并安装它，只有当它不是系统？

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 ?

我知道，如何确定，如果.NET Framework 4的是通过检查以下注册表项安装：

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

hasDotnet4 := RegKeyExists(HKEY_LOCAL_MACHINE, 
  'SOFTWAREMicrosoft.NETFrameworkpolicyv4.0');

如何基于上述检查我有条件地运行在.NET Framework 4的安装？

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

推荐答案

你可以做最简单的，就是用 检查 的参数，它可以让你控制，如果从 [文件] 部分将被提取，或者如果从一定程序 [运行] 部分将被执行。下面的脚本code显示了它的用法的条件安装.NET Framework 4的：

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, 'SOFTWAREMicrosoft.NETFrameworkpolicyv4.0');
end;