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# Package Gtk.Main

This package contains top-level subprograms that are used to initialize GtkAda and interact with the main event loop.

It also provides a set of packages to set up idle functions, timeout functions, and functions to be called before and after entering the main loop.

- Gtk.Main Types
- Gtk.Main Subprograms

## Types

    type Idle_Callback is access function return Boolean;
| Function that can be called automatically whenever GtkAda is not processing events. It should return True if the function should be called again as soon as possible, False if it should be unregistered.
    type Idle_Handler_Id is new Guint;
| Id for Idle handlers.
    type Idle_Priority is new Guint;
| Priorities that can be set for idle handlers. The higher the priority, the less urgent the task. Handlers whose priority is lower will be called before others.
    type Init_Function is access procedure
        (Data : System.Address);
| Function called just before starting the main loop. This can be registered with Init_Add below.
    type Quit_Function is access function return Boolean;
| Type of function that can be called when the main loop exits. It should return False if it should not be called again when another main loop exits.
    type Quit_Handler_Id is new Guint;
| registration ID for functions that will be called before the main loop exits.
    type Timeout_Callback is access function return Boolean;
| Function that can be called automatically at precise time intervals. It should return True if the function should be called again as soon as possible, False if it should be unregistered.
    type Timeout_Handler_Id is new Guint;
| Id for Timeout handlers.

## Subprograms

### Initialization and exit routines
    procedure Init;
| Initialize GtkAda's internal structures. This subprogram should be called before any other one in GtkAda. If GtkAda could not be initialized (no access to the display, etc.), the application exits with an error
    function Init_Check            return Boolean;
| Initialize GtkAda's internal structures. Return False if there was an error (no access to the display, etc.)
    procedure Gtk_Exit
      (Error_Code         : in     Gint);
| Terminate GtkAda cleanly, and quits the application.
    function Set_Locale            return String;
| Read and parse the local settings, such as time format, ... Return the name of the local settings, which can also be set with the environment variable LOCALE
    procedure Set_Locale;
| Read and parse the local settings, such as time format, ...
### Init and Quit functions
    procedure Init_Add
      (Func               :        Init_Function;
       Data               :        System.Address);
| Register a function to be called just before starting a main loop. This function is called only once, even if a new main loop is started recursively.
    function Quit_Add
      (Main_Level         :        Guint;
       Func               :        Quit_Function)
       return Quit_Handler_Id;
| Register a new function to be called when the current main loop exits. The function will be called once when the current main loop exists. If it returns False, it will then be deleted from the list of quit functions, and won't be called again next time a main loop is exited. The function will only be called when exiting a main loop at level Main_Level. If Main_Level is 0, the function will be called for the current main_loop.
    function Quit_Add_Destroy
      (Main_Level         :        Guint;
       Object             : access Gtk.Object.Gtk_Object_Record'Class)
       return Quit_Handler_Id;
| Ensure that Object is destroyed when exiting the main loop at Main_Level (or the current main loop level is 0).
    procedure Quit_Remove
      (Id                 :        Quit_Handler_Id);
| Remove a Quit Handler, that has been previously set by Quit_Add.
### The main loop
    function Events_Pending        return Boolean;
| Return True if there are some events waiting in the event queue.
    procedure Main;
| Start the main loop, and returns only when the main loop is exited. This subprogram can be called recursively, to start new internal loops. Each of these loops is exited through a call to Main_Quit. This is the recommended method to use when you want to popup a dialog and wait for the user answer before going any further. Note that this procedure can only be called within a single task.
    function Main_Level            return Guint;
| Return the level of the current main loop. Since there can be nested loops, this returns the depth of the current one, starting from 1 (0 if there is none).
    procedure Main_Quit;
| Quit the current main loop. If this was the last active main loop, no more events will be processed by GtkAda.
    function Main_Iteration
      (Blocking           : in     Boolean := True)
       return Boolean;
| Do one iteration of the main loop. Blocking indicates whether GtkAda should wait for an event to be available, or simply exit if there is none. Returns True if no main loop is running When doing some heavy calculations in an application, it is recommended that you check from time to time if there are any events pending and process them, so that your application still reacts to events. To do that, you would add a loop like: while Gtk.Main.Events_Pending loop Dead := Gtk.Main.Main_Iteration; end loop;
    procedure Do_Event
      (Event              : in     Gdk.Event.Gdk_Event);
| Process Event as if it was in the event queue. This function should almost never be used in your own application, this is the core function for event processing in GtkAda. The user should not free Event, this is already done by GtkAda.
    function Get_Event_Widget
      (Event              : in     Gdk.Event.Gdk_Event)
       return Gtk.Widget.Gtk_Widget;
| Return the widget to which Event applies.
### Grab functions
    procedure Grab_Add
      (Widget             : access Gtk.Widget.Gtk_Widget_Record'Class);
| Add a new widget to the grab list. The widget at the front of this list gets all the events even if it does not have the focus. This feature should be used with care. If you want a whole window to get the events, it is better to use Gtk.Window.Set_Modal instead which does the grabbing and ungrabbing for you. The grab is only done for the application. Events outside the application are still sent to their respective windows.
    procedure Grab_Remove
      (Widget             : access Gtk.Widget.Gtk_Widget_Record'Class);
| Remove a widget from the grab list.
    function Grab_Get_Current      return Gtk.Widget.Gtk_Widget;
| Return the widget that currently has the focus.
### Idle
GtkAda gives the possibility to register Idle functions. These are called every time there is no more event to process in the queue, and are used for instance internally to redraw widgets (so that the application keeps reacting to user input even if there is a heavy redrawing to do). The Idle function returns a boolean, which should be True if the idle remains active and should be called again, or False if the idle should be unregistered. The priority of these idle callbacks can also be modified, so that the scheduling calls one callback before another. Two versions are given, either with a user data or with none.
    function Idle_Add
      (Cb                 : in     Idle_Callback;
       Priority           : in     Idle_Priority
                           := Priority_Default_Idle)
       return Idle_Handler_Id;
| Register an idle callback with no user data.
    procedure Idle_Remove
      (Id                 : in     Idle_Handler_Id);
| Remove an idle callback, when its Id is known.
### Timeout
A timeout is a function that is called after a specified amount of time. You can of course use Ada tasks for the same role, however this might provide an easier way of doing things. In case your timeout function takes longer to execute than the specific delay (for instance it takes 200ms for an internal of 100ms), then no invocation is queued, and they are simply discarded. There is no queue of expired timers. On the other hand, standard events are still processed, but slowly (since they have the same priority as timeouts). The redrawing and resizing of widgets, which are being done as idles with lower priority will not take place.
    function Timeout_Add
      (Interval           : in     Guint32;
       Func               :        Timeout_Callback)
       return Timeout_Handler_Id;
| Add a new timeout. Func will be called after Interval milliseconds. The function will be as long as it returns True.
    procedure Timeout_Remove
      (Id                 : in     Timeout_Handler_Id);
| Unregister a timeout function.

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