QtScript -- script-side callback through C++-side implementation - c++

Question

The solution may be simple. Then again it may not be possible.
I have the base callback class:
class CFCallback {
int command_;
int transfer_rate_;
public:
CFCallback(int command, int transfer_rate = 0) {
command_ = command; transfer_rate_ = transfer_rate; }
virtual ~CFCallback() {}
virtual void operator()(void *data) = 0;
int GetCommand() { return command_; }
int GetTransferRate() { return transfer_rate_; }
};
And here's one example of deriving from CFCallback:
void CFPacketVersion::InitiateVersion() {
class InitiateVersionCB : public CFCallback {
CFPacketVersion *visitor_;
public:
InitiateVersionCB(CFPacketVersion *v, int command) :
CFCallback(command) {
visitor_ = v;
}
void operator()(void *data) {
Packet *pkt = (Packet *)data;
unsigned char *pkt_data = pkt->GetData();
std::string version = "";
for(unsigned int i = 0; i < pkt->GetDataLength(); i++ )
version+= pkt_data[i];
delete []pkt_data;
boost::regex rex("CFA(.*?):h(.*?),v(.*?)$");
boost::smatch what;
if( boost::regex_match(version, what, rex) ) {
if(visitor_->GetModel()->GetName() != what[1].str() )
LCDInfo("Crystalfontz: Model mismatch");
visitor_->SetHardwareVersion(what[2]);
visitor_->SetFirmwareVersion(what[3]);
}
}
};
GetVersion(new InitiateVersionCB(this, 1));
}
GetVersion(CFCallback *) is provided to the script engine.
I want to be able to do the same thing as seen in InitiateVersion, but on the javascript side of things. Is that possible?
I know I need to register meta type info for CFCallback. But I don't know if it's possible to use a pointer to a CFCallback. What I tried initially didn't work.
Also, seeing as CFCallback is a functor, I'm not sure how I translate that over to javascript. I imagine I can make CFCallback a QObject and provide a signal emitted from operator(). If you have any tips, please share.

Answer 1

I'm afraid it won't work the way you've set it up.
If you want to be able to create the callback in javascript, you need a QObject with an accessible GetVersion(QScriptValue) which the script will the use to pass a script-based implementation of the callback. Note, though, that the callback will not be able to work with untyped (void*) data - you need to pass either a valid QtScript object or QObject with a proper interface (like the Packet one in your example!)
You could then wrap it up like this:
QtScript:
function mycb(packet) {
var pkt_data = packet.getData(); // pkt_data is probably a String or custom object with proper interface so to simplify things get the version as string
var version = pkt_data.toString();
pkt_data.release(); // to simulate delete [] pkt_data; this is part of custom interface
// proceed further with the regex checks
}
GetVersion(mycb); // implies that you define the GetVersion() as a property of the global object
C++:
QScriptValue getVersion(QScriptContext *ctx, QScriptEngine *engine)
{
void *data = ...;
Packet pkt_data = wrapPacketData(data);
// Packet is interface registered with QtScript or inherits QObject
// it has methods getData(), toString() and release()
QScriptValueList args;
QScriptValue pkt_data_param = engine->newQObject(&pkt_data);
args << pkt_data_param;
QScriptValue cb = ctx->argument(0);
Q_ASSERT(cb.isFunction()); // we expect a function object!
cb.call(QScriptValue(), args);
}
QScriptValue getVersionFun = engine->newFunction(getVersion);
engine->globalObject().setProperty(QLatin1String("GetVersion"), getVersionFun);