QuickTime 4 Reference

Interrogating a Data Handler's Capabilities

While you can use the Component Manager's selection mechanisms to find a data handler component that can recognize data references of a specific type, your application must interact with the data handler in order to determine whether it can support a specific data reference. Apple has defined two functions, DataHCanUseDataRef and DataHGetVolumeList , that allow you to query a data handler component in order to find out whether it can work with a data reference. By using these two functions, your application can choose a data handler that is best-suited to its specific needs.

Using the DataHCanUseDataRef function, you supply a data reference to the data handler component. The component then reports what it can do with that data reference. The returned value indicates the level and, to some extent, the quality of service the data handler can provide (for example, whether the component can read data from or write data to the data reference and whether the component uses any special support when working with that data reference).

Because calling the DataHCanUseDataRef function in several data handlers can be time consuming, Apple has also defined a function that helps narrow the search. By using the DataHGetVolumeList function, your application can obtain a list of all the file system volumes that a data handler can support. In response to your request, the data handler returns the list and flags indicating the level and quality of service the data handler can provide for containers on that volume.

For more information on these functions, see "Selecting a Data Handler" .