vb.net - Correct way to get an interface / object from an interface pointer? -

having known nothing interfaces until now, having remarkably hard time trying implement solution given this question.

i think correctly getting pointer ishellfolder interface, don't seem able use pointer. how usable interface when having pointer?

the code below shows doing , suspect problems.

first, interface delarations:

' have wrapped interfaces in own namespace, "binarusshell". ' have declared every interface's functions / subs in same order in .idl files of windows platform sdk 7.1. ' every function / sub has <preservesig()> attribute can see native return values when debugging. ' i'd keep question lean possible, showing few functions per interface. ' of course, have implemented of them (as in respective .idl file).  namespace binarusshell    <comimport()> _   <interfacetype(cominterfacetype.interfaceisiunknown)> _   <guid("000214fa-0000-0000-c000-000000000046")> _   public interface iextracticon      ' above guid guid unicode version of interface, i.e. iextracticonw.     ' therefore, unicode variant of strings used in parameters of following functions.     ' see include files of windows sdk done way well.      <preservesig()> function geticonlocation(byval uflags uinteger,                                              <marshalas(unmanagedtype.lpwstr, sizeparamindex:=2)> byval psziconfile string,                                              byval cchmax uinteger,                                              byref piindex integer,                                              byref pwflags uinteger) integer      ' ...     ' here comes second function (iextracticon has two) ...     ' ...        end interface    <comimport()> _   <interfacetype(cominterfacetype.interfaceisiunknown)> _   <guid("000214e6-0000-0000-c000-000000000046")> _   public interface ishellfolder      <preservesig()> function getuiobjectof(<[in]()> byval hwndowner intptr,                                            <[in]()> byval cidl uinteger,                                            <[in]()> <marshalas(unmanagedtype.lparray, sizeparamindex:=1)> byval apidl() intptr,                                            <[in]()> <marshalas(unmanagedtype.lpstruct)> byval riid guid,                                            <[in](), out()> byref rgfreserved uinteger,                                            <out()> byref ppv intptr) integer      ' ...     ' here come other functions ...     ' ...    end interface  end namespace 

second, windows api declarations, , third, function want implement (this stuck):

' windows api declarations in class win32api. ' class not wrapped in namespace. ' keep question lean possible, leaving out declarations of constants or guids. ' have taken of them literally windows platform sdk 7.1.  public class win32api    <dllimport("shell32.dll", charset:=charset.auto)> _   private shared function shbindtoparent(<[in]()> byval pidl intptr,                                          <[in]()> <marshalas(unmanagedtype.lpstruct)> byval riid guid,                                          <out()> byref ppv intptr,                                          <out()> byref ppidllast intptr) integer   end function    <dllimport("shell32.dll", charset:=charset.auto)> _   private shared function shgetknownfolderidlist(<[in]()> <marshalas(unmanagedtype.lpstruct)> byval rfid guid,                                                  <[in]()> byval dwflags uinteger,                                                  <[in]()> byval htoken intptr,                                                  <out()> byref ppidl intptr) integer   end function  ' -----------------------------------------------------  ' function implement in class win32api well. ' function @ stage nothing useful outer world; ' meant code stepping through debugger. ' comments below show result of every step , understanding has happened.    public shared function icontest() boolean      dim ui_returnflags uinteger     dim i_result integer     dim intptr_currentpidlabsolute intptr,         intptr_parentishellfolder intptr,         intptr_currentiextracticon intptr     dim arintptr_relpidlist(0) intptr     dim ishellfolder_parent binarusshell.ishellfolder     dim iextracticon_extractor binarusshell.iextracticon      i_result = shgetknownfolderidlist(folderid_system, 0, 0, intptr_currentpidlabsolute)     ' above seems work. i_result 0 means success, ,     ' intptr_currentpidlabsolute has reasonable value now.      i_result = shbindtoparent(intptr_currentpidlabsolute, iid_ishellfolder, intptr_parentishellfolder, arintptr_relpidlist(0))     ' above seems work. i_result 0 means success, ,     ' intptr_parentishellfolder , arintptr_relpidlist(0) have reasonable values now.      ' problems begin. have no clue how interface / object     ' intptr_parentishellfolder can use within vb.net.     ' therefore, have tried following (but believing wrong):     ishellfolder_parent = directcast(marshal.getobjectforiunknown(intptr_parentishellfolder), binarusshell.ishellfolder)     ' not throw error, have no clue happening.     ' marshal.getobjectforiunknown, name implies, should return object     ' encapsulates iunknown interface, giving pointer ishellfolder     ' interface, wonder why doesn't freak out. original idea     ' try way believe ishellfolder inherits iunknown,     ' *eventually* work way. comment that?      i_result = ishellfolder_parent.getuiobjectof(0, 1, arintptr_relpidlist, iid_iextracticon, ui_returnflags, intptr_currentiextracticon)     ' point puzzled. i_result still 0,     ' means success, intptr_currentiextracticon 0 well, meaning     ' has gone horribly wrong. according understanding of     ' msdn documentation, getuiobjectof must not return s_ok if     ' has gone wrong; in other words, if returns s_ok, intptr_currentiextracticon     ' must set reasonable value. explain what's happening?      ' have left out rest of function because wouldn't make sense     ' use null pointer further action.    end function  end class 

any ideas doing wrong? docs, got impression every folder item (virtual or not) , file exposes iextracticon.

answering own question: when defining ishellfolder interface in vb.net, had forgotten include bindtofolder() function (you shouldn't try implement things @ 03:00 a.m., notably if had no clue of things until 1 hour before).

of course, documented everywhere, made ishellfolder interface produce wrong results (again not knowing talking about, since bindtofolder() comes before getuiobjectof() in interface definition, , latter in turn comes before getdisplaynameof(), imagine getdisplaynameof() has been called when code called getuiobjectof(), explain weird results).

now have corrected ishellfolder definition (i.e. have added missing function) , have double-checked other interface definitions (those without errors), , works expected.