Data Container API

One of the basic building blocks used through Concord is the Data Container API. This API is implemented in the DkmDataContainer class and a few other related types. The basic idea of the data container API is to allow ‘virtual fields’ to be added to all the important objects. This is similar to the 'expando' concept JavaScript, though it doesn’t have the same type safety or namespace pollution problems that JavaScript expandos have.

The API works by having components add ‘data items’ to a data container object. The caller can then obtain the data item back when they need to. Thus the implementation class for a Concord component is usually has little state, and instead uses the data container objects to do the work of holding onto the state. This ensures that state is uniformly cleaned up across Concord rather than having a situation where each component is responsible for finding an appropriate place to clean up their state. For this reason, components generally do not need to remove their data items but can rather just wait for the data items to be automatically removed when the container object is closed. More information on this subject is in the Hello World sample as well as in the API documentation.