using System;

using System.Xml;

using System.Xml.Linq;                  

using System.Xml.XPath;

​

public class Program

{

    public static void Main()

    {

        var simpleXml = @"<?xml version=""1.0"" encoding=""utf-8""?>

            <App>

                <Properties>

                    <Title>Simple title</Title>

                </Properties>

            </App>

            ";

        var manifestXml = @"<?xml version=""1.0"" encoding=""utf-8""?>

<!--Published:70EDFC97-B41D-43C5-B751-7C00AD999804-->

<!--Created:cb85b80c-f585-40ff-8bfc-12ff4d0e34a9-->

<App xmlns=""http://schemas.microsoft.com/sharepoint/2012/app/manifest"" Name=""CosoSpExSyncSharePointAddIn"" ProductID=""{af6fa0c5-a448-46a5-8c3a-55e5b5c05db5}"" Version=""1.0.8.8"" SharePointMinVersion=""15.0.0.0"">

  <Properties>

    <Title>Connect Bridge SharePoint To Exchange Sync</Title>

    <StartPage>https://cnsc-rdp-01.contoso.com/CS.CBSpExSync.SharePoint.AddInWeb/?{StandardTokens}</StartPage>

    <UninstallingEventEndpoint>https://cnsc-rdp-01.contoso.com/CS.CBSpExSync.SharePoint.AddInWeb/Services/AppEventReceiver.svc</UninstallingEventEndpoint>

    <InstalledEventEndpoint>https://cnsc-rdp-01.contoso.com/CS.CBSpExSync.SharePoint.AddInWeb/Services/AppEventReceiver.svc</InstalledEventEndpoint>

    <UpgradedEventEndpoint>https://cnsc-rdp-01.contoso.com/CS.CBSpExSync.SharePoint.AddInWeb/Services/AppEventReceiver.svc</UpgradedEventEndpoint>

    <SupportedLocales>

      <SupportedLocale CultureName=""en"" />

      <SupportedLocale CultureName=""en-US"" />

      <SupportedLocale CultureName=""de-DE"" />

      <SupportedLocale CultureName=""de"" />

    </SupportedLocales>

  </Properties>

  <AppPrincipal>

    <RemoteWebApplication ClientId=""8ed4760e-1b5a-4284-9a30-df2322573066"" />

  </AppPrincipal>

  <AppPermissionRequests AllowAppOnlyPolicy=""true"">

    <AppPermissionRequest Scope=""http://sharepoint/content/sitecollection/web"" Right=""Manage"" />

  </AppPermissionRequests>

  <RemoteEndpoints>

    <RemoteEndpoint Url=""https://SA1220001.zmssrveas.com:8080/"" />

    <RemoteEndpoint Url=""https://cnsc-rdp-01.contoso.com:10503/"" />

    <RemoteEndpoint Url=""https://cnsc-rdp-01.contoso.com:44303/"" />

    <RemoteEndpoint Url=""https://exchangebridge.anyshare.ch:8080"" />

    <RemoteEndpoint Url=""https://exchangebridge.t.anyshare.ch:8080"" />

    <RemoteEndpoint Url=""https://client-demo.westeurope.cloudapp.azure.com:8080"" />

    <RemoteEndpoint Url=""https://client-demo.westeurope.cloudapp.azure.com/"" />

  </RemoteEndpoints>

</App>";

        //my initial attempt

        var manifestDoc = XDocument.Parse(manifestXml);

        var titleElem = manifestDoc.XPathSelectElement("//App/Properties/Title");

        //attempt using nsman according stack overflow

        var nsMan = new XmlNamespaceManager(new NameTable());

        nsMan.AddNamespace("man","http://schemas.microsoft.com/sharepoint/2012/app/manifest");

        var titleElemUsingNsMan = manifestDoc.XPathSelectElement("//man:App/Properties/Title",nsMan);

        //a simple xml without any xmlns works as expected

        var simpleDoc = XDocument.Parse(simpleXml);

        var simpleTitleElem = simpleDoc.XPathSelectElement("//App/Properties/Title");

        Console.WriteLine("title elem value: {0}", titleElem==null ? "null" : titleElem.Value);

        Console.WriteLine("title elem value using nsMan: {0}", titleElemUsingNsMan==null ? "null" : titleElemUsingNsMan.Value);

        Console.WriteLine("simple title elem value: {0}", simpleTitleElem==null ? "null" : simpleTitleElem.Value);

    }

}