> Greg Ercolano wrote:
>
> > Note that with this technique, 'this' can be passed to the
> > callback, so that it has access to this instance of the class. eg:
> >
> > static void Sample_Callback(Fl_Widget*, void *data) {
> > MyMenuBar *mmb = (MyMenuBar*)data; // get 'this'
> > mmb->xxx(); // now can access non-static
> > class elements/methods
> > }
> > [..]
> > MyMenuBar(int X,int Y,int W,int H):Fl_Menu_Bar(X,Y,W,H) {
> > add("&File/&Sample", 0, Sample_Callback, (void*)this); // <-- pass
> > 'this' to cb
> > }
>
> Here's an example that shows this in action.
>
> This opens two windows, each with its own instance of the custom
> menubar. Each menubar instance has unique, instance specific data
> that the static callback can access when the File -> Do Callback
> item is chosen by the user in each window:
>
> ---- snip
> #include <stdio.h>
> #include <time.h>
> #include <FL/Fl.H>
> #include <FL/Fl_Window.H>
> #include <FL/Fl_Menu_Bar.H>
> //
> // Example of derived menubar class with callback that can access class
> instance data -erco 12/07/10
> //
> class MyMenuBar : public Fl_Menu_Bar {
> const char *id_; // instance-specific data
> public:
> void id(const char* val) { id_ = val; }
> const char* id() const { return(id_); }
> static void MenuCallback(Fl_Widget *, void *data) {
> // Show how we can access instance-specific data
> MyMenuBar *mmb = (MyMenuBar*)data;
> printf("Sample callback, instance '%s'\n", mmb->id());
> }
> MyMenuBar(int X,int Y,int W,int H):Fl_Menu_Bar(X,Y,W,H) {
> add("&File/&Do Callback", 0, MenuCallback, (void*)this); //
> passes 'this' to cb when invoked
> }
> };
> int main() {
> // WINDOW #1 + MENUBAR
> Fl_Window w1(0,0,400,400,"Window #1");
> MyMenuBar m1(0,0,400,25);
> m1.id("Menu #1"); // set instance specific data
> w1.end();
> w1.show();
>
> // WINDOW #2 + MENUBAR
> Fl_Window w2(400,0,400,400,"Window #2");
> MyMenuBar m2(0,0,400,25);
> m2.id("Menu #2"); // set instance specific data
> w2.end();
> w2.show();
>
> return(Fl::run());
> }
> ---- snip
Beautiful, thanks Greg. These little snippets of code would be great for the
programming manual.
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