dirk/C++/gtkmm/is_visible

Ravensburg, 10-02-13

is_visible – What Does It Return?

Today, I was thinking about Gtk::Widget::show(), Gtk::Widget::hide(), and Gtk::Widget::is_visible(). My gtkmm manual isn't really a help – documentation for these methods is missing. I could had a look in the GTK+ manual but decided to make a sample application, instead.

These methods seem rather simple to use at the first glance. However, if a certain behaviour is granted this can really simplify code. Thus, I had two questions in mind:

  1. Does Gtk::Widget::is_visible() return whether widget has been set to be visible, or whether it is really displayed?
  2. Are Gtk::Widget::show()/Gtk::Widget::hide() safe against double call?

Source Code

Text Fileis_visible.cc
/** @file sample about show(), hide(), and is_visible()
 *
 * Last CVS checkin:
 * $Date: $
 * $Author: scheff $
 */

/**************************************************************************/

// standard C/C++ header:
#include <iostream>

// Gnome header:
#include <gtkmm/button.h>
#include <gtkmm/main.h>
#include <gtkmm/window.h>

using namespace std;

/**************************************************************************/

class Window: public Gtk::Window {

  // methods:
  protected:
    /// @name Overloaded Event Handling
    //@{

    /// called when widget becomes visible.
    virtual void on_show(void);

    /// called when widget becomes invisible.
    virtual void on_hide(void);

    //@}
};

/**************************************************************************/

// Overloaded Event Handling

void Window::on_show(void)
{
  cout << "Window::on_show()" << endl;
  Gtk::Window::on_show();
}

void Window::on_hide(void)
{
  cout << "Window::on_hide()" << endl;
  Gtk::Window::on_hide();
}

/**************************************************************************/

/// called when button has been clicked.
static void onBtnClicked(Window *pWin)
{
  cout << "win.is_visible(): " << (pWin->is_visible() ? "true" : "false")
    << endl;
}

/** waits for user confirm.
 *
 * @param action text with next action
 */
static void pause(const char *action)
{
  cout << "Press [ENTER] to " << action << ": " << flush;
  string str; getline(cin, str);
}

/** provides the main function of application.
 *
 * @param argc number of command line arguments
 * @param argv pointer to array of pointers to strings with command line
 *        arguments
 * @return 0 ... application exited regularly\n
 *         else ... execution of application aborted
 */
int main(int argc, char *argv[])
{
  // init
  pause("start");
  {
    Gtk::Main gtkMain(argc, argv);
    // init GUI
    Window win;
    Gtk::Button gtkBtn("is_visible()");
    gtkBtn.signal_clicked().connect(
      sigc::bind<0>(sigc::ptr_fun(&onBtnClicked), &win));
    gtkBtn.show();
    win.add(gtkBtn);
    cout << "Before gtkMain.run(win):" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl;
    // run
    gtkMain.run(win);
    cout << "After gtkMain.run(win):" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl;
  }
  pause("continue");
  {
    Gtk::Main gtkMain(argc, argv);
    // init GUI
    Window win;
    Gtk::Button gtkBtn("is_visible()");
    win.add(gtkBtn);
    cout
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl
      << "gtkBtn.is_visible(): " << (gtkBtn.is_visible()? "true" : "false")
      << endl;
    gtkBtn.show();
    cout << "gtkBtn.show();" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl
      << "gtkBtn.is_visible(): " << (gtkBtn.is_visible()? "true" : "false")
      << endl;
    gtkBtn.hide();
    cout << "gtkBtn.hide();" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl
      << "gtkBtn.is_visible(): " << (gtkBtn.is_visible()? "true" : "false")
      << endl;
    win.show();
    cout << "win.show();" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl
      << "gtkBtn.is_visible(): " << (gtkBtn.is_visible()? "true" : "false")
      << endl;
    win.show();
    cout << "win.show();" << endl
      << "win.is_visible(): " << (win.is_visible() ? "true" : "false")
      << endl
      << "gtkBtn.is_visible(): " << (gtkBtn.is_visible()? "true" : "false")
      << endl;
    cout << "gtkMain.run(win)" << endl;
    gtkMain.run(win);
  }
  // done
  pause("finish");
  return 0;
}

I compiled this sample on Linux with:

                                                                                
> g++ -o is_visible `pkg-config gtkmm-2.4 --cflags --libs` is_visible.cc↵
>

Output

Console: 
                                                                                
Press [ENTER] to start: ↵
Before gtkMain.run(win):
win.is_visible(): false
Window::on_show()
Snapshot
is_visible Snapshot 1
Console/Interaction:
Press [ENTER] to start:
Before gtkMain.run(win):
win.is_visible(): false
Window::on_show()
click on the is_visible button
win.is_visible(): true
click on the Quit button
Window::on_hide()
After gtkMain.run(win):
win.is_visible(): false
Press [ENTER] to continue: ↵
win.is_visible(): false
gtkBtn.is_visible(): false
gtkBtn.show();
win.is_visible(): false
gtkBtn.is_visible(): true
gtkBtn.hide();
win.is_visible(): false
gtkBtn.is_visible(): false
Window::on_show()
win.show();
win.is_visible(): true
gtkBtn.is_visible(): false
win.show();
win.is_visible(): true
gtkBtn.is_visible(): false
gtkMain.run(win)
Snapshot
is_visible Snapshot 1
Console/Interaction:
click on the Quit button
Window::on_hide()
Press [ENTER] to finish: ↵

Conclusion

This looks fine. :-) (I'm rather not surprised. It does what I expected.)

  1. Gtk::Widget::is_visible() returns true, after Gtk::Widget::show() has been called. This is even true when the parent window is not (yet) visible.
  2. Gtk::Widget::show()/Gtk::Widget::hide() are safe against double calls.

Files

Text Fileis_visible.ccC++ source code
MS Visual C++ 2008 Project Fileis_visible.vcprojMS Visual C++ 2008 project file

dirk/C++/gtkmm/is_visible

Last modified: Thu Feb 25 17:38:34 2010