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# Wx::App

The App class represents the whole GUI application itself. It is the
container within which all GUI code runs. It is used to:

- set and get application-wide properties;
- implement the windowing event loop to respond to user actions;
- initiate the application via App#on_init;
- allow default processing of events not handled by other objects in the application.

## Running an app

No GUI code can run before an App starts – all Windows,
Frames, Brushes, Pens,
Colours, and Icons must be created after the
app has been started, otherwise wxRuby will raise an
exception. Therefore, a Wx::App is responsible for setting up the
initial state of the application’s windows. There are two ways to do
this.

The first, simpler way is just to use the Wx::App.run class
method. Pass this method a block specifying how to set up the initial
windows in the app; this code will run, and the App will then wait for
the user to interact with the application:

Wx::App.run do f = Wx::Frame.new(nil, :title => ‘basic app’) f.show end

The second way is appropriate for more complex applications. In this
case, define a subclass of Wx::App, and describe what it should do
on start up (display frames) within an `on_init` method. Then create an
instance of this class, and call its `main_loop` method.

class MyApp < Wx::App def on_init f = Wx::Frame.new(nil, :title => ‘basic app’) f.show end end app = MyApp.new app.main_loop

This method is more suitable for complex apps because it allows you to
define global custom methods and behaviours in the App class, and to
override the default handling of events or exceptions using
filter_event or on_run.

## Exception handling

To handle ruby exceptions within wxRuby applications, override
on_init to trap those occurring at init time, or
on_run to trap exceptions in the main loop. See
on_run for an example of exception handling.

## Accessing the application instance

Any wxRuby program will have a single instance of Wx::App, which can be
accessed once the app has started by the constant `Wx::THE_APP`, or by
the module method `Wx::get_app()`.

## Derived from

EvtHandler

Object

## See also

App overview

## Methods

- App.new
- App.run
- App#dispatch
- App#exit_main_loop
- App#filter_event
- App#get_app_name
- App#get_class_name
- App#get_exit_on_frame_delete
- App#get_top_window
- App#get_use_best_visual
- App#get_vendor_name
- App#is_active
- App#is_main_loop_running
- App#main_loop
- App#on_assert_failure
- App#on_exit
- App#on_init
- App#on_run
- App#pending
- App#set_app_name
- App#set_class_name
- App#set_exit_on_frame_delete
- App#set_top_window
- App#set_use_best_visual
- App#set_vendor_name
- App#yield

### App.new

Creates a new Application, but does not run it; to start the
and enter its event loop, call main_loop on the
instance.

### App.run

Wx::App.run { … }

Creates a new App and starts its main loop, using the code in the passed
block to set up the initial state of the Windows.

### App#dispatch

dispatch()

Dispatches the next event in the windowing system event queue.

This can be used for programming event loops, e.g.

while (app.Pending()) Dispatch();

#### See also

App#pending

### App#exit_main_loop

exit_main_loop()

Call this to explicitly exit the main message (event) loop.
You should normally exit the main loop (and the application) by deleting
the top window.

### App#filter_event

Integer filter_event(%(arg-type)Event% event)

This function is called before processing any event and allows the application
to preempt the processing of some events. If this method returns $-1$ the event
is processed normally, otherwise either `true` or `false` should be
returned and the event processing stops immediately considering that the event
had been already processed (for the former return value) or that it is not
going to be processed at all (for the latter one).

### App#get_app_name

String get_app_name()

Returns the application name.

#### Remarks

Widgets sets this to a reasonable default before
calling App#on_init, but the application can reset it at will.

### App#get_class_name

String get_class_name()

Gets the class name of the application. The class name may be used in a platform specific
manner to refer to the application.

#### See also

App#set_class_name

### App#get_exit_on_frame_delete

Boolean get_exit_on_frame_delete()

Returns true if the application will exit when the top-level window is deleted, false
otherwise.

#### See also

App#set_exit_on_frame_delete,

App shutdown overview

### App#get_top_window

Window get_top_window()

Returns a pointer to the top window.

#### Remarks

If the top window hasn’t been set using App#set_top_window, this
function will find the first top-level window (frame or dialog) and return that.

#### See also

set_top_window

### App#get_use_best_visual

Boolean get_use_best_visual()

Returns true if the application will use the best visual on systems that support
different visuals, false otherwise.

#### See also

set_use_best_visual

### App#get_vendor_name

String get_vendor_name()

Returns the application’s vendor name.

### App#is_active

Boolean is_active()

Returns `true` if the application is active, i.e. if one of its windows is
currently in the foreground. If this function returns `false` and you need to
attract users attention to the application, you may use
TopLevelWindow#request_user_attention
to do it.

### App#is_main_loop_running

Boolean is_main_loop_running()

Returns `true` if the main event loop is currently running, i.e. if the
application is inside on_run or main_loop.

This can be useful to test whether the events can be dispatched. For example,
if this function returns , non-blocking sockets cannot be used because
the events from them would never be processed.

### App#main_loop

Integer main_loop()

Calling this method starts up the application, calling its `on_init`
method.

#### Return value

Returns 0 under X, and the wParam of the WM_QUIT message under Windows.

### App#on_assert_failure

on_assert_failure(%(arg-type)Char% file, Integer line, Char cond, Char msg)

This method is called when an assert failure occurs, i.e. a condition
specified in the WxWidgets C++ library evaluates to `false`. It is only
called if WxWidgets was compiled in debug mode (when `__WXDEBUG__` is
defined); note that standard releases of WxRuby are compiled without
this option.

#### Parameters

- file the name of the source file where the assert occurred
- line the line number in this file where the assert occurred
- cond the condition of the failed assert in string form
- msg the failure message, may be `nil` if just ASSERT or FAIL was used

### App#on_exit

Integer on_exit()

Override this member function for any processing which needs to be
done as the application is about to exit. OnExit is called after
destroying all application windows and controls, but before
Widgets cleanup. Note that it is not called at all if
on_init failed.

The return value of this function is currently ignored, return the same value
as returned by the base class method if you override it.

### App#on_init

Boolean on_init()

This must be provided by the application, and will usually create the
application’s main window, optionally calling
App#set_top_window. You may use
on_exit to clean up anything initialized here, provided
that the function returns .

Notice that if you want to to use the command line processing provided by
Widgets you have to call the base class version in the derived class
OnInit().

Return `true` to continue processing, `false` to exit the application
immediately.

### App#on_run

Integer on_run()

This virtual function is where the execution of a program written in
Widgets starts. The default implementation just enters the main loop and
starts handling the events until it terminates, either because
exit_main_loop has been explicitly called or because
the last frame has been deleted and
get_exit_on_frame_delete flag is `true`
(this is the default).

The return value of this function becomes the exit code of the program,
so it should return `0` in case of successful termination.

In wxRuby this is the place for a general exception handler that will
catch exception raised in any event handler. Here is an example that
will simply print the exception to STDOUT and continue the event loop:

def on_run super rescue Exception => e puts e.message retry end

### App#pending

Boolean pending()

Returns true if unprocessed events are in the window system event queue.

#### See also

App#dispatch

### App#set_app_name

set_app_name(%(arg-type)String% name)

Sets the name of the application. The name may be used in dialogs
(for example by the document/view framework). A default name is set by
Widgets.

#### See also

App#get_app_name

### App#set_class_name

set_class_name(%(arg-type)String% name)

Sets the class name of the application. This may be used in a platform specific
manner to refer to the application.

#### See also

App#get_class_name

### App#set_exit_on_frame_delete

set_exit_on_frame_delete(%(arg-type)Boolean% flag)

Allows the programmer to specify whether the application will exit when the
top-level frame is deleted.

#### Parameters

- flag If true (the default), the application will exit when the top-level frame is
  deleted. If false, the application will continue to run.

#### See also

App#get_exit_on_frame_delete,

App shutdown overview

### App#set_top_window

set_top_window(%(arg-type)Window% window)

Sets the `top’ window. You can call this from within App#on_init to
let Widgets know which is the main window. You don’t have to set the top window;
it is only a convenience so that (for example) certain dialogs without parents can use a
specific window as the top window. If no top window is specified by the application,
Widgets just uses the first frame or dialog in its top-level window list, when it
needs to use the top window.

#### Parameters

- window The new top window.

#### See also

App#get_top_window, App#on_init

### App#set_vendor_name

set_vendor_name(%(arg-type)String% name)

Sets the name of application’s vendor. The name will be used
in registry access. A default name is set by
Widgets.

#### See also

App#get_vendor_name

### App#set_use_best_visual

set_use_best_visual(%(arg-type)Boolean% flag)

Allows the programmer to specify whether the application will use the best visual
on systems that support several visual on the same display. This is typically the
case under Solaris and IRIX, where the default visual is only 8-bit whereas certain
applications are supposed to run in TrueColour mode.

Note that this function has to be called in the constructor of the `App`
instance and won’t have any effect when called later on.

This function currently only has effect under GTK.

#### Parameters

- flag If true, the app will use the best visual.

### App#yield

Boolean yield(%(arg-type)Boolean% onlyIfNeeded = false)

Yields control to pending messages in the windowing system. This can be useful, for example, when a
time-consuming process writes to a text window. Without an occasional
yield, the text window will not be updated properly, and on systems with
cooperative multitasking, such as Windows 3.1 other processes will not respond.

Caution should be exercised, however, since yielding may allow the
user to perform actions which are not compatible with the current task.
Disabling menu items or whole menus during processing can avoid unwanted
reentrance of code: see ::SafeYield for a better
function.

Note that Yield() will not flush the message logs. This is intentional as
calling Yield() is usually done to quickly update the screen and popping up a
message box dialog may be undesirable. If you do wish to flush the log
messages immediately (otherwise it will be done during the next idle loop
iteration), call Log#flush_active.

Calling Yield() recursively is normally an error and an assert failure is
raised in debug build if such situation is detected. However if the
onlyIfNeeded parameter is `true`, the method will just silently
return `false` instead.

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