QtScript newFunction won't work

[ihoss]

I love the new QtScript module added to Qt 4.3, and I got the engine to do exactly what I wanted very quickly. But now I'm trying to add functions to the engine, specifically one that prints the arguments in a QTextEdit. I have looked at the documentation for QScriptEngine::newFunction, bit I just can't get it to work. Here is my code:

QScriptValue printString(QScriptContext *context, QScriptEngine *engine){
	for(int i=0; i<context->argumentCount(); i++){
		//outputText->append(context->argument(i).toString());
	}
	return context->callee();
}
void MainWindow::setupScripts(){
	engine = new QScriptEngine();
	QScriptValue fun = engine->newFunction(printString);
	engine->globalObject().setProperty("print", fun, QScriptValue::ReadOnly | QScriptValue::Undeletable);
}

QScriptValue printString(QScriptContext *context, QScriptEngine *engine){
	for(int i=0; i<context->argumentCount(); i++){
		//outputText->append(context->argument(i).toString());
	}
	return context->callee();
}
void MainWindow::setupScripts(){
	engine = new QScriptEngine();
	QScriptValue fun = engine->newFunction(printString);
	engine->globalObject().setProperty("print", fun, QScriptValue::ReadOnly | QScriptValue::Undeletable);
}

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Whenever the code is compiled, I get the following error:

...:error: no matching function for call to `QScriptEngine::newFunction(<unknow type>)`

...:error: no matching function for call to `QScriptEngine::newFunction(<unknow type>)`

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Anyone know why this might be?

[jacek]

Is printString() in the same .cpp file as MainWindow::setupScripts()?

[ihoss]

yup

Wow, yup is too short for me to post just that

[jacek]

yup

Is that the first error you get? Do you have QT += script in your .pro file?

[ihoss]

It is the first error, and I do have QT += script in the pro file. The thing is that the code compiles if I remove the newFunction line, and the compiled program works like intended.

[jacek]

The thing is that the code compiles if I remove the newFunction line, and the compiled program works like intended.

Is printString() defined before MainWindow::setupScripts()?

[ihoss]

I've uploaded the entire project so you can have a look at it. I have commented out the part that creates the new function. It's almost at the bottom of the cpp file.

[jacek]

The problem is that you have declared printString() method in MainWindow class and it takes precedence over printString() function. Just remove line #28 from mainwindow.h. Also you have to fix MainWindow::htmlize() -- it shouldn't return a reference.

[ihoss]

Thanks a lot, I had no idea why it wouldn't work

[ihoss]

Hokay, so I got it to work, but not the way I intended. What I want is for the print function to print something to the QTextEdit called outputText. Since the printString function is called as a static function, it can't point to outputText. I have tried lots of ways to get it to work, but all of them seem to throw some errors. Any idea how I can fix it?

[jacek]

What I want is for the print function to print something to the QTextEdit called outputText.

You need a global variable or a singleton object to achieve this.

[ihoss]

Hmm, I tried that, but I got an error with the .o compiled object file. It kept saying that it couldn't find the object that I made static. I don't have the code here, but what I did was to make a static variable which pointed to the QTextEdit I wanted to change. Then I initialized it in the constructor. I think this might have caused the error, since it wasn't 100% certain that the variable was initialized before it was retrieved in the static function called by the QtScript function. I'll post the code as soon as I get home if you don't already know what I messed up

[ihoss]

Ok, so I worked around the problem by adding the instance of the current class, which only has one public slot, write, to the engine as an object called document. Then I added a script function called print that called document.write. It works This assumes that you only have one public slot. If you have lots of stuff that you want to hide, then create a new class which inherits from QObject and add that to the script engine. Here is the code:

engine = new QScriptEngine();
QScriptValue that = engine->newQObject(this, QScriptEngine::QtOwnership, QScriptEngine::ExcludeChildObjects
		| QScriptEngine::ExcludeSuperClassMethods | QScriptEngine::ExcludeSuperClassProperties);
engine->globalObject().setProperty("document",that);
engine->evaluate("function print(str){return document.write(str);};");

engine = new QScriptEngine();
QScriptValue that = engine->newQObject(this, QScriptEngine::QtOwnership, QScriptEngine::ExcludeChildObjects
		| QScriptEngine::ExcludeSuperClassMethods | QScriptEngine::ExcludeSuperClassProperties);
engine->globalObject().setProperty("document",that);
engine->evaluate("function print(str){return document.write(str);};");

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[jacek]

Then I added a script function called print that called document.write. It works This assumes that you only have one public slot. If you have lots of stuff that you want to hide, then create a new class which inherits from QObject and add that to the script engine.

This is a very good solution and quite similar to the singleton approach.