我们可以通过注册表查找系统已安装的.NET Framework版本

.NET Framework版本号的注册表位置位于 HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full

比如，如果值大于等于461308 并且 小于461808 ，那么版本就是4.7.1

打开.NET Framework项的注册表项。

using ( Microsoft.Win32.RegistryKey ndpKey =
	Microsoft.Win32.RegistryKey.OpenRemoteBaseKey( Microsoft.Win32.RegistryHive.LocalMachine, "" )
	.OpenSubKey( @"SOFTWARE\Microsoft\NET Framework Setup\NDP\" ) )
{
	// As an alternative, if you know the computers you will query are running .NET Framework 4.5 or later, you can use:
	// using ( Microsoft.Win32.RegistryKey ndpKey =
	// 	Microsoft.Win32.RegistryKey.OpenBaseKey( Microsoft.Win32.RegistryHive.LocalMachine, Microsoft.Win32.RegistryView.Registry32 )
	// 	.OpenSubKey( @"SOFTWARE\Microsoft\NET Framework Setup\NDP\" ) )
	foreach ( string versionKeyName in ndpKey.GetSubKeyNames( ) )
	{
		if ( versionKeyName.StartsWith( "v" ) )
		{
			Microsoft.Win32.RegistryKey versionKey = ndpKey.OpenSubKey( versionKeyName );
			string name = (string) versionKey.GetValue( "Version", "" );
			string sp = versionKey.GetValue( "SP", "" ).ToString( );
			string install = versionKey.GetValue( "Install", "" ).ToString( );
			if ( install == "" ) //no install info, must be later.
			{
				System.Console.WriteLine( versionKeyName + "  " + name );
			}
			else
			{
				if ( sp != "" && install == "1" )
				{
					System.Console.WriteLine( versionKeyName + "  " + name + "  SP" + sp );
				}
			}
			if ( name != "" )
			{
				continue;
			}
			foreach ( string subKeyName in versionKey.GetSubKeyNames( ) )
			{
				Microsoft.Win32.RegistryKey subKey = versionKey.OpenSubKey( subKeyName );
				name = (string) subKey.GetValue( "Version", "" );
				if ( name != "" )
				{
					sp = subKey.GetValue( "SP", "" ).ToString( );
				}
				install = subKey.GetValue( "Install", "" ).ToString( );
				if ( install == "" ) //no install info, must be later.
				{
					System.Console.WriteLine( versionKeyName + "  " + name );
				}
				else
				{
					if ( sp != "" && install == "1" )
					{
						System.Console.WriteLine( "  " + subKeyName + "  " + name + "  SP" + sp );
					}
					else if ( install == "1" )
					{
						System.Console.WriteLine( "  " + subKeyName + "  " + name );
					}
				}
			}
		}
	}
}

查看已安装的.NET Framework版本的函数

const string subkey = @"SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\";

using (var ndpKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry32).OpenSubKey(subkey))
{
    if (ndpKey != null && ndpKey.GetValue("Release") != null)
    {
        Console.WriteLine($".NET Framework Version: {CheckFor45PlusVersion((int)ndpKey.GetValue("Release"))}");
    }
    else
    {
        Console.WriteLine(".NET Framework Version 4.5 or later is not detected.");
    }
}

// Checking the version using >= enables forward compatibility.
static string CheckFor45PlusVersion(int releaseKey)
{
    if (releaseKey >= 528040)
        return "4.8 or later";
    if (releaseKey >= 461808)
        return "4.7.2";
    if (releaseKey >= 461308)
        return "4.7.1";
    if (releaseKey >= 460798)
        return "4.7";
    if (releaseKey >= 394802)
        return "4.6.2";
    if (releaseKey >= 394254)
        return "4.6.1";
    if (releaseKey >= 393295)
        return "4.6";
    if (releaseKey >= 379893)
        return "4.5.2";
    if (releaseKey >= 378675)
        return "4.5.1";
    if (releaseKey >= 378389)
        return "4.5";
    // This code should never execute. A non-null release key should mean
    // that 4.5 or later is installed.
    return "No 4.5 or later version detected";
}

还可以使用命令行查找

(Get-ItemProperty "HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full").Release -ge 394802