Step 3. Support QueryInterface

Step 3. Support QueryInterface

To expose the filter's new interfaces to clients, do the following: 

• Include the DECLARE_IUNKNOWN macro in the public declaration section of your filter:

  public:
  DECLARE_IUNKNOWN;
  

• Override CUnknown::NonDelegatingQueryInterface to check for the IIDs of the two interfaces:

STDMETHODIMP CGrayFilter::NonDelegatingQueryInterface(REFIID riid, void **ppv)
{
    if (riid == IID_ISpecifyPropertyPages)
    {
        return GetInterface(
           static_cast<ISpecifyPropertyPages*>(this),
           ppv);
    }
    else if (riid == IID_ISaturation)
    {
        return GetInterface(static_cast<ISaturation*>(this), ppv);
    }
    else
    {
        // Call the parent class.
        return CBaseFilter::NonDelegatingQueryInterface(riid, ppv);

        // NOTE: This example assumes that the filter inherits directly
        // from CBaseFilter. If your filter inherits from another class,
        // call the NonDelegatingQueryInterface method of that class.
    }
}

Next: Step 4. Create the Property Page.

See Also

• Creating a Filter Property Page
• How to Implement IUnknown