Chapter 2. Tutorials

This first tutorial is repeated from the DataHub Scripting manual.

The Code

The code that gets written to the MyApp.g file is as follows:

require ("Application");

/* Get the Gamma library functions and methods for ODBC and/or
 * Windows programming.  Uncomment either or both. */

require ("WindowsSupport");
//require ("ODBCSupport");

/* Applications share the execution thread and the global name
 * space, so we create a class that contains all of the functions
 * and variables for the application.  This does two things:
 *   1) creates a private name space for the application, and
 *   2) allows you to re-load the application to create either
 *      a new unique instance or multiple instances without
 *      damaging an existing running instance.
 */
class MyApp Application
{
    window;
}

/* Use methods to create functions outside the 'main line'. */
method MyApp.samplemethod ()
{
}

/* Write the 'main line' of the program here. */
method MyApp.constructor ()
{
    local    rect = CreateRect (0, 0, 300, 300), txt;
    .window = new GWindow();
    
    .window.Create (0, rect, "Hello", WS_OVERLAPPEDWINDOW, 0);
    .window.CenterWindow();
    txt = .window.CreateControl (GStatic, 0, 0, 280, 22, "Hello world", SS_CENTER);
    txt.CenterWindow();
    .window.MessageHandler (WM_DESTROY, `destroy(@self));
    .window.ShowWindow (SW_SHOW);
}

/* Any code to be run when the program gets shut down. */
method MyApp.destructor ()
{
    // The WM_DESTROY message could come before or after this destructor depending
    // on whether the application instance is destroyed or the window is closed
    // first.  We protect against the case where the window is closed first.
    if (instance_p(.window) && .window.GetHwnd() != 0)
        .window.PostMessage (WM_CLOSE, 0, 0);
    MessageBox(0, string ("Application: ", class_name(self), " completed."), "Done", 0);
}

/* Start the program by instantiating the class.  If your
 * constructor code does not create a persistent reference to
 * the instance (self), then it will be destroyed by the
 * garbage collector soon after creation.  If you do not want
 * this to happen, assign the instance to a global variable, or
 * create a static data member in your class to which you assign
 * 'self' during the construction process.  ApplicationSingleton()
 * does this for you automatically. */
ApplicationSingleton (MyApp);