Delphi2005学习笔记2——Using Platform Invoke with Delphi 2005[7]

" namespace="ms-help://borland.bds3" keywords="system.runtime.interopservices.gchandle">gchandle , although relatively easy, is fairly expensive in terms of performance. it also has the possibility of resource leaks if handles aren’t freed correctly. if object references are maintained in the managed code, it is possible to pass a unique index, for example the hash code returned by the gethashcode method, to the unmanaged api instead of an object reference. a hash table can be maintained on the managed side to facilitate retrieving an object instance from a hash value if needed. an example of using this technique can be found in the ttreenodes class (in borland.vcl.comctrls). using com interfaces when using com interfaces, a similar approach is taken as when using unmanaged api’s. the interface needs to be declared, using custom attributes to describe the type interface and the guid. next the methods are declared; using the same approach as for unmanaged api’s. the following example uses the iautocomplete interface, defined as follows in delphi 7:

iautocomplete = interface(iunknown)
  ['{00bb2762-6a77-11d0-a535-00c04fd7d062}']
  function init(hwndedit: hwnd; punkacl: iunknown;
    pwszregkeypath: lpcwstr; pwszquickcomplete: lpcwstr): hresult; stdcall;
  function enable(fenable: bool): hresult; stdcall;
end;

[comimport, guidattribute('00bb2762-6a77-11d0-a535-00c04fd7d062'), interfacetypeattribute(cominterfacetype.interfaceisiunknown)]
iautocomplete = interface
  function init(hwndedit: hwnd; punkacl: ienumstring;
    pwszregkeypath: intptr; pwszquickcomplete: intptr): hresult;
  function enable(fenable: bool): hresult;
end;