Reflection GetValue fails for Uri class

Question

I want to get access to the m_Info field of Uri class to change some fields inside. but uriInfo.GetValue(uri) returns null.

 var uri = new Uri("https://stackoverflow.com/questions/12993962/set-value-of-private-field"); var uriInfo = typeof(Uri).GetField("m_Info", BindingFlags.NonPublic | BindingFlags.Instance); var infoField = uriInfo.GetValue(uri);

the code works fine for my test class with the same structure as Uri but it fails for the System.Uri class. Any ideas?

What makes you think that the xamarin / android version has a field called m_Info? it is not required to share an implementation with the .NET Framework implementation. And on a protected environment such as android: it is not required to let you have access to the insides at all. What is it that returns null? is it the GetField? or the GetValue? — Marc Gravell
– Marc Gravell, Commented Jun 22, 2017 at 9:05
GetField does NOT return null. GetValue does. That makes me think like that. — Radiofisik
– Radiofisik, Commented Jun 22, 2017 at 9:14

Marc Gravell · Accepted Answer · 2017-06-22 09:21:38Z

Quite simply: m_Info isn't assigned in that code-path; it is lazily assigned when first needed. Locally, this works:

object infoField = uriInfo.GetValue(uri); // null var port = uri.Port; // forces it to initialize infoField = uriInfo.GetValue(uri); // not null

Note, however, that this approach is itself not fully encompassing; looking in reflector for .Port, this would only apply for "simple syntax" (whatever that means):

if (this.m_Syntax.IsSimple) { this.EnsureUriInfo(); } else { this.EnsureHostString(false); } if (this.InFact(Flags.HostNotParsed | Flags.NotDefaultPort)) { return this.m_Info.Offset.PortValue; } return this.m_Syntax.DefaultPort;

The point being: guaranteeing that m_Info has a value is non-trivial. You might want to try invoking the EnsureInfoInfo() method first via reflection.

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