The Be Book - System Overview - The Storage Kit
BNodeInfo provides file type information about a particular node;
specifically:
The (MIME) file type.
The node's icons, including the node-specific icon that the Tracker displays.
The "preferred app"; this is the application that's used to access the node's contents.
Except for the Tracker icon, all this information can also be set through
the BNodeInfo class. None of the information is passed on to the File
Type database; if you want to record a node's file type information with
the database, you have to create a
BMimeType object (based on the node's
file type) and go from there.
You initialize a BNodeInfo object by passing it a
BNode object. Although
you can pass any flavor of node, you typically only care about files;
passing a BFile
object (or any subclass of
BNode) is, of course,
acceptable. The BNodeInfo object maintains its own pointer to the BNode
you pass in. You don't have to avoid touching the
BNode while a BNodeInfo
is looking at it (or changing it); the only thing you shouldn't do is
delete the BNode.
BNodeInfo doesn't care if the
BNode is locked—there's no particular
reason to lock the
BNode before passing it in,
but the BNodeInfo won't
balk if you do. If you pass in a
BFile object,
BNodeInfo does not obey
the BFile's
read/write flags. For example, you can set the node info for
a BFile
even if you've opened it in read-only mode.
The BNodeInfo class does nothing more than look in a node's attributes
for the information it sets or gets. The attribute names for the various
information particles are given in the function descriptions, below. If
you want, you can bypass BNodeInfo and get the node information directly
by passing the attribute names to
BNode's
ReadAttr() and
WriteAttr()
functions.
The one exception to this is
GetTrackerIcon(): This function starts by
looking in the node's attributes, but then it goes out hunting if it has
to (if the icon isn't found in the attributes).
BNodeInfo has a single subclass:
BAppFileInfo.
You use a BAppFileInfo
object to get more information about a specific executable image (file).
