In addition to WM_WINDOW_DELETE
you need to listen for and handle the ClientMessage
event.
Modifying the example from Rosetta Code to illustrate:
#include <X11/Xlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void) {
Display *d;
Window w;
XEvent e;
const char *msg = "Hello, World!";
int s;
d = XOpenDisplay(NULL);
if (d == NULL) {
fprintf(stderr, "Cannot open display\n");
exit(1);
}
s = DefaultScreen(d);
w = XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, 100, 100, 1, BlackPixel(d, s), WhitePixel(d, s));
XSelectInput(d, w, ExposureMask | KeyPressMask);
XMapWindow(d, w);
// I support the WM_DELETE_WINDOW protocol
Atom WM_DELETE_WINDOW = XInternAtom(d, "WM_DELETE_WINDOW", False);
XSetWMProtocols(d, w, &WM_DELETE_WINDOW, 1);
while (1) {
XNextEvent(d, &e);
if (e.type == Expose) {
XFillRectangle(d, w, DefaultGC(d, s), 20, 20, 10, 10);
XDrawString(d, w, DefaultGC(d, s), 10, 50, msg, strlen(msg));
}
else if (e.type == KeyPress)
break;
else if (e.type == ClientMessage)
// TODO Should check here for other client message types -
// however as the only protocol registered above is WM_DELETE_WINDOW
// it is safe for this small example.
break;
}
XCloseDisplay(d);
return 0;
}