[Kde-java] Re: GCJ (Re: Build system for KDE4)

[Richard Dale]

On Monday 20 June 2005 10:13, Thomas Zander wrote:
> On Sunday 19 June 2005 22:35, Richard Dale wrote:
> [snip signal/slot discussion]
>
> >  On the other hand, I think it's useful to
> > have an option close to the C++ api to make it easy to convert code
> > from C++ to java.
>
> Realistically; how many people will do that?
Pretty much eveyone, because nearly all the documentation for Qt and KDE is 
C++ based, including the code snippets. I've found ruby or java programmers 
who can't program in C++, can manage to read the docs though. They just need 
to learn a few basics like a 'char *', 'QString' and 'QCString' are all 
Strings in ruby or java.

> But ok, if the implementation is there, we can use it. No need to throw
> work away.
> I assume the example code you typed uses a base object QObject?  Or how
> does an object know the SLOT method in your Java example?
They're defined in Qt.java, which is a superclass of QObject.java:

	/** Prepend a '2' to a signal string and remove any spaces */
	public static String SIGNAL(String signal) {
		return "2" + sqeezeOut(signal, ' ');
	}
	
	/** Prepend a '1' to a slot string and remove any spaces */
	public static String SLOT(String slot) {
		return "1" + sqeezeOut(slot, ' ');
	}

emit() is defined in QObject.java:

	public native void emit(String signal, Object[] args);

	protected void emit(String signal) {
		Object[] args = new Object[0];
		emit("2" + signal.trim() + "()", args);
	}

	protected void emit(String signal, Object value) {
		Object[] args = new Object[1];
		args[0] = value;
		emit("2" + signal.trim() + "(" + value.getClass().getName() + ")", args);
	}
...

There are lots of different overloaded methods for the various arg types, and 
just one native method that they all map onto.

I would like to change it to look like this:

protected Proxy emit();

There would be a version in each subclass of QObject. The interfaces supported 
by the Proxy returned by emit() would be all the <classname>Signals.java 
interfaces for the class and it's superclasses. QPopupMenu has a signals 
interface like this:

public interface QPopupMenuSignals {
	void activated(int itemId);
	void highlighted(int itemId);
	void activatedRedirect(int itemId);
	void highlightedRedirect(int itemId);
	void aboutToShow();
	void aboutToHide();
}

So to emit a signal from a subclass of QPopupMenu, you would cast the Proxy to 
the appropriate interface:

((QPopupMenuSignals) emit()).activate(3)

Instead of the signal name being a string, it is a method in an interface, and 
the emit call is type safe and can be checked at compile time.

-- Richard