解决方法
获取文件扩展名,并在注册表中查找.它的条目将具有“内容类型”属性.
这是从控制器操作返回FilePathResult的完整示例：
string filePysicalPath,fileName; //these need to be set to your values.
var reg = Microsoft.Win32.Registry.ClassesRoot.OpenSubKey( Path.GetExtension( filename ).ToLower() );
string contentType = "application/unknown";
if ( reg != null )
{
string registryContentType = reg.GetValue( "Content Type" ) as string;
if ( !String.IsNullOrWhiteSpace( registryContentType ) )
{
contentType = registryContentType;
}
}
return File( filePysicalPath,contentType,filename );
