BPropertyInfo¶
BPropertyInfo
is a simple class that manages scripting. A
program describes its scripting interface to a BPropertyInfo
object through an array of property_info
structures, with each entry describing a piece of the scripting suite.
A BPropertyInfo
is instantiated by passing a zero-terminated
array of property_info
to its constructor. A
typical initialization looks like:
static property_info prop_list[] = {
{ "duck",
{ B_GET_PROPERTY, B_SET_PROPERTY, 0 },
{ B_DIRECT_SPECIFIER, B_INDEX_SPECIFIER, 0 },
"get or set duck"
},
{ "head",
{ B_GET_PROPERTY, 0 },
{ B_DIRECT_SPECIFIER, 0 },
"get head"
},
{ "head",
{ B_SET_PROPERTY, 0 },
{ B_DIRECT_SPECIFIER, 0 },
"set head"
},
{ "feet",
{0}, {0}, "can do anything with his orange feet"
},
0 // terminate list};
BPropertyInfo prop_info(prop_list);
Since BPropertyInfo
only stores a pointer to the array, it is
important that the life span of the array is at least as long as that of
the BPropertyInfo
object.
Notice that BPropertyInfo
doesn’t impose any particular
structure upon the array; in particular, not all commands and specifiers
for a given property need be placed in a single entry in the array. You are
free to organize your scripting suite in whatever manner is most convenient
for your particular object.
BPropertyInfo
is a descendant of BFlattenable
,
and can therefore be used to store a description of an object’s supported
scripting suite. This is particularly useful when overriding
GetSupportedSuites()
:
status_t MyHandler::GetSupportedSuites(BMessage *msg)
{
msg->AddString("suites", "suite/vnd.Me-my_handler");
BPropertyInfo prop_info(prop_list);
msg->AddFlat("messages", &prop_info);
return baseClass::GetSupportedSuites(msg);
}
Naturally, BPropertyInfo
is equally as useful in interpreting
the results obtained from querying an object for its supported suites.
BPropertyInfo
defines the FindMatch()
method designed to simplify the implementation
of ResolveSpecifier()
. It returns
the index of the property info matching the description given to it, or -1
if none match. This reduces ResolveSpecifier()
in the simplest cases to:
BHandler*
MyHandler::ResolveSpecifier(BMessage* msg, int32 index,
BMessage* spec, int32 form,
const char* prop)
{
BPropertyInfo prop_info(prop_list);
if (prop_info.FindMatch(msg, index, spec, form, prop) >= 0)
return this;
return baseClass::ResolveSpecifier(msg, index, spec, form,
prop);
}
Of course, for more complicated objects, ResolveSpecifier()
may need to set the target handler to an
object other than itself, so more processing may be required. In those
cases, the object can use the index returned by FindMatch()
to help it determine the target of the
scripting message.