通过读取注册表项或通过查询 Internet Explorer 中的用户代理字符串，可以检测是否已安装了 .NET Framework 3.5。
读取注册表项安装成功完成后，.NET Framework 3.5 安装程序会写入注册表项。通过检查下表中列出的注册表项，可以检测是否安装了 .NET Framework 3.5。
| 注册表项名称 | 值 |
| HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.5 | 名称：Install 类型：DWORD 数据：1 |
| HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform | 名称：Version 类型：REG_SZ 数据：.NET CLR 3.5.build number |
当计算机上安装了 .NET Framework 3.5 后，.NET Framework 3.5 版本号将显示为浏览器标头中报告的用户代理字符串的一部分。以下示例演示了一个示例页，该页使用 JavaScript 检测并报告是否安装了 .NET Framework 3.5。
<html>
<head>
<title>Test for .NET Framework 3.5</title>
<meta HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=utf-8" />
<script type="text/JavaScript">
<!--
var NETFX3RuntimeVersion = "3.5.21022";
function body_onload()
{
var result = document.getElementById("result");
if (HasRuntimeVersion(NETFX3RuntimeVersion))
{
result.innerHTML = "This machine has the correct version of the .NET Framework 3.5 runtime: "
+ NETFX3RuntimeVersion + "."
+ "\n\nThis machine's userAgent string is: "
+ navigator.userAgent + ".";
}
else
{
result.innerHTML = "The .NET Framework version 3.5 is not installed on this computer.<br/>"
+ "Click <a href='http://msdn.microsoft.com/windowsvista/default.aspx'>"
+ " here</a> to get the .NET Framework 3.5 now.";}
}
//
// Retrieve the version from the user agent string and compare with specified version.
//
function HasRuntimeVersion(versionToCheck)
{
var userAgentString =
navigator.userAgent.match(/.NET CLR 3.5.[0-9]+/g);
if (userAgentString != null)
{
var i;
for (i = 0; i < userAgentString.length; ++i)
{
if (CompareVersions(GetVersion(versionToCheck),
GetVersion(userAgentString[i])) <= 0)
return true;
}
}
return false;
}
//
// Extract the numeric part of the version string.
//
function GetVersion(versionString)
{
var numericString = versionString.match(/([0-9]+)\.([0-9]+)\.([0-9]+)/i);
return numericString.slice(1);
}
//
// Compare the version strings by converting them to numeric format.
//
function CompareVersions(version1, version2)
{
for (i = 0; i < version1.length; ++i)
{
var number1 = new Number(version1[i]);
var number2 = new Number(version2[i]);
if (number1 < number2)
return -1;
if (number1 > number2)
return 1;
}
return 0;
}
-->
</script>
</head>
<body onload="body_onload();">
<div id="result" ></div>
</body>
</html>
如果搜索字符串“.NET Framework 3.5”版本成功，将显示以下消息：
This machine has the correct version of the .NET Framework 3.5: 3.5.28015.00.
This machine's userAgent string is: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.5.28015.00).
（根据测试 .NET Framework 时使用的不同浏览器和浏览器版本，用户代理字符串的详细信息会略有不同。）
如果没有安装“.NET Framework 3.5”，将显示以下消息：
The .NET Framework version 3.5 is not installed on this computer.
Click here to get the .NET Framework 3.5 now.
转载于:https://www.cnblogs.com/sqshine/archive/2009/03/26/1422433.html
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