高手看下gtkmm的绘图问题

Question

以下是一段画线段的代码，为什么窗口出现一下就跳掉了呢，如何才能使画图之后的窗口还保持不消失啊？
File: myarea.h
#ifndef GTKMM_EXAMPLE_MYAREA_H
#define GTKMM_EXAMPLE_MYAREA_H
#include <gtkmm/drawingarea.h>
class MyArea : public Gtk:rawingArea
{
public:
MyArea();
virtual ~MyArea();
protected:
//Override default signal handler:
virtual bool on_expose_event(GdkEventExpose* event);
};
#endif // GTKMM_EXAMPLE_MYAREA_H
File: main.cc
#include "myarea.h"
#include <gtkmm/main.h>
#include <gtkmm/window.h>
int main(int argc, char** argv)
{
Gtk::Main kit(argc, argv);
Gtk::Window win;
win.set_title("DrawingArea";
MyArea area;
win.add(area);
area.show();
Gtk::Main::run(win);
return 0;
}
File: myarea.cc
#include "myarea.h"
#include <cairomm/context.h>
MyArea::MyArea()
{
}
MyArea::~MyArea()
{
}
bool MyArea:n_expose_event(GdkEventExpose* event)
{
// This is where we draw on the window
Glib::RefPtr<Gdk::Window> window = get_window();
if(window)
{
Gtk::Allocation allocation = get_allocation();
const int width = allocation.get_width();
const int height = allocation.get_height();
// coordinates for the center of the window
int xc, yc;
xc = width / 2;
yc = height / 2;
Cairo::RefPtr<Cairo::Context> cr = window->create_cairo_context();
cr->set_line_width(10.0);
// clip to the area indicated by the expose event so that we only redraw
// the portion of the window that needs to be redrawn
cr->rectangle(event->area.x, event->area.y,
event->area.width, event->area.height);
cr->clip();
// draw red lines out from the center of the window
cr->set_source_rgb(0.8, 0.0, 0.0);
cr->move_to(0, 0);
cr->line_to(xc, yc);
cr->line_to(0, height);
cr->move_to(xc, yc);
cr->line_to(width, yc);
cr->stroke();
}
return true;
}

[ 本帖最后由 凯尔特之魂 于 2009-5-8 19:13 编辑 ]