ArcGIS Engine Developer Guide

C++ APPLICATION PROGRAMMING INTERFACE
• “button_press_event”—the signal to respond to. Here you will listen for the
button being pressed. For other options, see the GTK reference at the end of
this topic.
• ClickCallback—the function to call when the signal is received.
• NULL—data to pass into the callback function. Here there is no data the
function will need, so NULL is passed.
Callback functions
For the callback to work, you must implement the function that is being called
on the event. Callbacks will generally follow the following function signature:
Make sure that the data passed to
callback_data will be in scope later when the
callback routine is executed.
void callback_func(GtkWidget *widget, gpointer callback_data);
However, as in this case, you will sometimes want additional information about
the event. To get that information, the following function signature can be used:
void ClickCallback(GtkWidget *widget, GdkEventButton *event, gpointer
callback_data);
The parameters are:
• widget—the widget that gave the signal
• event—tells what button press or release event triggered the function
• callback_data—any data passed into the function, as indicated in the last
parameter of g_signal_connect
For this example, place this function after main in pbExample.cpp, and have it
print to cerr which mouse button was used to click (for example, “button:
1”). Remember to also place a forward declaration of it before main.
To get the button that was clicked, you must use the information in the
GdkEventButton struct.
void ClickCallback(GtkWidget *widget, GdkEventButton *event,
gpointer callback_data)
{
// show which button was clicked
std::cerr