{"id":44843,"date":"2015-01-23T07:00:00","date_gmt":"2015-01-23T22:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2015\/01\/23\/helper-functions-to-make-shell-bind-contexts-slightly-more-manageable\/"},"modified":"2019-03-13T12:12:19","modified_gmt":"2019-03-13T19:12:19","slug":"20150123-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20150123-00\/?p=44843","title":{"rendered":"Helper functions to make shell bind contexts slightly more manageable"},"content":{"rendered":"

Last time, we learned about the wonderful world of shell bind context strings<\/a>, and I promised some helper functions to make this slightly more manageable. <\/p>\n

Here are some helper functions which supplement the Create­Bind­Ctx­With­Opts<\/code> function<\/a> we created some time ago. <\/p>\n

\n#include <propsys.h>\n\nHRESULT EnsureBindCtxPropertyBag(\n    IBindCtx *pbc, REFIID riid, void **ppv)\n{\n *ppv = nullptr;\n CComPtr<IUnknown> spunk;\n HRESULT hr = pbc->GetObjectParam(STR_PROPERTYBAG_PARAM, &spunk);\n if (FAILED(hr)) {\n  hr = PSCreateMemoryPropertyStore(IID_PPV_ARGS(&spunk));\n  if (SUCCEEDED(hr)) {\n   hr = pbc->RegisterObjectParam(STR_PROPERTYBAG_PARAM, spunk);\n  }\n }\n if (SUCCEEDED(hr)) {\n  hr = spunk->QueryInterface(riid, ppv);\n }\n  return hr;\n}\n\nHRESULT AddBindCtxDWORD(\n    IBindCtx *pbc, LPCWSTR pszName, DWORD dwValue)\n{\n CComPtr<IPropertyBag> sppb;\n HRESULT hr = EnsureBindCtxPropertyBag(pbc, IID_PPV_ARGS(&sppb));\n if (SUCCEEDED(hr)) {\n  hr = PSPropertyBag_WriteDWORD(sppb, pszName, dwValue);\n }\n return hr;\n}\n\nHRESULT AddBindCtxString(\n    IBindCtx *pbc, LPCWSTR pszName, LPCWSTR pszValue)\n{\n CComPtr<IPropertyBag> sppb;\n HRESULT hr = EnsureBindCtxPropertyBag(pbc, IID_PPV_ARGS(&sppb));\n if (SUCCEEDED(hr)) {\n  hr = PSPropertyBag_WriteStr(sppb, pszName, pszValue);\n }\n return hr;\n}\n\nHRESULT CreateDwordBindCtx(\n    LPCWSTR pszName, DWORD dwValue, IBindCtx **ppbc)\n{\n CComPtr<IBindCtx> spbc;\n HRESULT hr = CreateBindCtx(0, &spbc);\n if (SUCCEEDED(hr)) {\n  hr = AddBindCtxDWORD(spbc, pszName, dwValue);\n }\n *ppbc = SUCCEEDED(hr) ? spbc.Detach() : nullptr;\n return hr;\n}\n\nHRESULT CreateStringBindCtx(\n    LPCWSTR pszName, LPCWSTR pszValue, IBindCtx **ppbc)\n{\n CComPtr<IBindCtx> spbc;\n HRESULT hr = CreateBindCtx(0, &spbc);\n if (SUCCEEDED(hr)) {\n  hr = AddBindCtxString(spbc, pszName, pszValue);\n }\n *ppbc = SUCCEEDED(hr) ? spbc.Detach() : nullptr;\n return hr;\n}\n<\/pre>\n
The Ensure­Bind­Ctx­Property­Bag<\/code> function puts a property bag in the bind context if there isn’t one already. <\/p>\n
The Add­Bind­Ctx­DWORD<\/code> function adds a DWORD<\/code> to that associated property bag. If you wanted to add multiple DWORD<\/code>s to a bind context, you would call this function multiple times. You can also use the Add­Bind­Ctx­String<\/code> if the thing you want to add is a string. <\/p>\n
The Create­Dword­Bind­Ctx<\/code> function handles the simple case where you want to create a bind context that contains a single DWORD<\/code>. Similarly, Create­String­Bind­Ctx<\/code>. <\/p>\n
But now things are starting to get kind of unwieldy. What if you want a bind context with a string and a DWORD<\/code>? Let’s go for something a bit more fluent. <\/p>\n
But first, some scaffolding. <\/p>\n
\nclass CStaticUnknown : public IUnknown\n{\npublic:\n \/\/ *** IUnknown ***\n IFACEMETHODIMP QueryInterface(\n  _In_ REFIID riid, _Outptr_ void **ppv)\n {\n  *ppv = nullptr;\n  HRESULT hr = E_NOINTERFACE;\n  if (riid == IID_IUnknown) {\n   *ppv = static_cast<IUnknown *>(this);\n   AddRef();\n   hr = S_OK;\n  }\n  return hr;\n }\n\n IFACEMETHODIMP_(ULONG) AddRef()\n {\n  return 2;\n }\n\n IFACEMETHODIMP_(ULONG) Release()\n {\n  return 1;\n }\n\n};\n\nCStaticUnknown s_unkStatic;\n<\/pre>\n
This static implementation of IUnknown<\/code> is one we’ll use for the bind context strings whose mere presence indicates that a flag is set. <\/p>\n
\nclass CBindCtxBuilder\n{\npublic:\n CBindCtxBuilder()\n {\n  m_hrCumulative = CreateBindCtx(0, &m_spbc);\n }\n\n CBindCtxBuilder& SetMode(DWORD grfMode);\n CBindCtxBuilder& SetFindData(const WIN32_FIND_DATA *pfd);\n CBindCtxBuilder& SetFlag(PCWSTR pszName);\n CBindCtxBuilder& SetVariantDword(PCWSTR pszName, DWORD dwValue);\n CBindCtxBuilder& SetVariantString(PCWSTR pszName, PCWSTR pszValue);\n\n HRESULT Result() const { return m_hrCumulative; }\n\n IBindCtx *GetBindCtx() const\n { return SUCCEEDED(m_hrCumulative) ? m_spbc : nullptr; }\nprivate:\n HRESULT EnsurePropertyBag();\n\nprivate:\n CComPtr<IBindCtx> m_spbc;\n CComPtr<IPropertyBag> m_sppb;\n HRESULT m_hrCumulative;\n};\n<\/pre>\n
The bind context builder class is a helper class that creates a bind context, and then fills it with stuff. For now, we let you set the following: <\/p>\n