Install a listener for the global data storage

Wouldn't it be nice if your plug-in if your plugin would be notified on changed in the data manager like when a file is opened? Yes it definitly would be nice. So this is how you do it:

mitk::DataStorage::Pointer storage = GetDefaultDataStorage();

storage->AddNodeEvent.AddListener(
   mitk::MessageDelegate1<YOURPLUGIN, const mitk::DataNode*>(
   this, &YOURPLUGIN::YOURPLUGINFUNCTION ));

First get a pointer to the default data storage. It's member variable AddNodeEvent, itself a typedef, offers the AddListener function. Use a mitk::MessageDelegate1 as parameter. MessageDelegate1 takes the type of your plug-in and a return value, in this case a mitk::DataNode pointer to effectivly create a delegate. Delegates are not part of C++, so this object is effectivly a delegate implementation taking a this pointer (google can help you if you don't know what this means). At last give the constructor of the delegate a this pointer and a function pointer to your listerner function.

That's it. If a node is added to the data storage the given listener function is called with a pointer to the added node. Further steps can be taken from here.

There are additional listener functions like DeleteNodeEvent, RemoveNodeEvent and ChangeNodeEvent. Implement them all for fame and glory.