Next Previous

Retired Document

Important: This document may not represent best practices for current development. Links to downloads and other resources may no longer be valid.

Loading and Using a Plug-in

The code example in Listing 1 shows how a plug-in host can load and use a plug-in. It searches registered plug-ins for one that implements a test interface. If found, it invokes functions using the interface.

CFPlugInFindFactoriesForPlugInType searches all the registered plug-ins and returns an array of all factories that can create the requested type.
For each factory, CFPlugInInstanceCreate creates an instance of the test type and obtains a pointer to its IUnknown interface, if that exists.
The IUnknown interface is tested to determine if it is the test interface. If it is, one of its functions is invoked and a flag is set to stop the search.

Listing 1 Loading and using a plug-in

Boolean foundInterface = false;

// Create a URL that points to the plug-in using a CFString path 'aPath'.

CFURLRef url =

    CFURLCreateWithFileSystemPath(NULL, aPath, kCFURLPOSIXPathStyle, TRUE);

// Create a CFPlugin using the URL.

// This causes the plug-in's types and factories to be registered with the system.

// The plug-in's code is not loaded unless it is using dynamic registration.

CFPlugInRef plugin = CFPlugInCreate(NULL, url);

if (!plugin)

    printf("Could not create CFPluginRef.\n");

else

    // Test whether this plug-in implements the Test type.

    CFArrayRef factories = CFPlugInFindFactoriesForPlugInType(kTestTypeID);

    // If there are factories for the requested type, attempt to

    // get the IUnknown interface.

    if (factories != NULL)

        CFIndex factoryCount = CFArrayGetCount(factories);

        if (factoryCount <= 0)

            printf("Could not find any factories.\n");

        else

            CFIndex index;

            for (index = 0;

                (index < factoryCount) && (!foundInterface);

                index++)

                // Get the factory ID at the current index.

                CFUUIDRef factoryID =

                            CFArrayGetValueAtIndex(factories, index);

                // Use the factory ID to get an IUnknown interface.

                // The code for the PlugIn is loaded here.

                IUnknownVTbl **iunknown =

                    CFPlugInInstanceCreate(NULL, factoryID, kTestTypeID);

                // If this is an IUnknown interface,

                // query for the Test interface.

                if (iunknown)

                    TestInterfaceStruct **interface = NULL;

                    (*iunknown)->QueryInterface(iunknown,

                                CFUUIDGetUUIDBytes(kTestInterfaceID),

                                (LPVOID *)(&interface));

                    // Finished with IUnknown.

                    (*iunknown)->Release(iunknown);

                    // If this is a Test interface, try to call its function.

                    if (interface)

                        (*interface)->fooMe(interface, TRUE);

                        (*interface)->fooMe(interface, FALSE);

                        // Finished with test interface.

                        // This causes the plug-in's code to be unloaded.

                        (*interface)->Release(interface);

                        foundInterface = true;

                // end of iunknown

            // end of index loop

        // factoryCount > 0

        // Release the factories array.

        CFRelease(factories);

    if (!foundInterface)

        printf("Failed to get interface.\n");

    // Release the CFPlugin -- memory for the plug-in is deallocated here.

    CFRelease(plugin);

Next Previous