EventLoopBase

Base class for all event loop implementations.

An event loop is a class which queries the queue of native events sent to the wxWidgets application and dispatches them to the appropriate EvtHandlers.

An object of this class is created by AppTraits.CreateEventLoop and used by App to run the main application event loop. Temporary event loops are usually created by Dialog.ShowModal .

You can create your own event loop if you need, provided that you restore the main event loop once yours is destroyed (see EventLoopActivator).

See also

App, EventLoopActivator

Inheritance Diagram

Inheritance diagram for class EventLoopBase

Methods Summary

Dispatch	Dispatches the next event in the windowing system event queue.
DispatchTimeout	Dispatch an event but not wait longer than the specified timeout for it.
Exit	Exit from the loop with the given exit code.
GetActive	Return the currently active (running) event loop.
IsEventAllowedInsideYield	Returns True if the given event category is allowed inside a YieldFor call (i.e.
IsMain	Returns True if this is the main loop executed by App.OnRun .
IsOk	Use this to check whether the event loop was successfully created before using it.
IsRunning	Return True if this event loop is currently running.
IsYielding	Returns True if called from inside Yield or from inside YieldFor .
Pending	Return True if any events are available.
ProcessIdle	This virtual function is called when the application becomes idle and normally just sends IdleEvent to all interested parties.
Run	Start the event loop, return the exit code when it is finished.
SetActive	Set currently active (running) event loop.
WakeUp	Called by wxWidgets to wake up the event loop even if it is currently blocked inside Dispatch .
WakeUpIdle	Makes sure that idle events are sent again.
Yield	Yields control to pending messages in the windowing system.
YieldFor	Works like Yield with onlyIfNeeded == True, except that it allows the caller to specify a mask of the EventCategory values which indicates which events should be processed and which should instead be “delayed” (i.e.

Class API

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class EventLoopBase(object)

Base class for all event loop implementations.

Methods

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Dispatch(self)

Dispatches the next event in the windowing system event queue.

Blocks until an event appears if there are none currently (use Pending if this is not wanted).

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

while evtloop.Pending():
    evtloop.Dispatch()

Return type:bool Returns:False if the event loop should stop and True otherwise.

See also

Pending , EventLoopBase

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DispatchTimeout(self, timeout)

Dispatch an event but not wait longer than the specified timeout for it.

If an event is received before the specified timeout expires, it is processed and the function returns 1 normally or 0 if the event loop should quite. Otherwise, i.e. if the timeout expires, the functions returns -1 without processing any events.

Parameters:timeout (long) – The maximal time to wait for the events in milliseconds. Return type:int Returns:1 if an event was processed, 0 if the event loop should quit or -1 if the timeout expired.

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Exit(self, rc=0)

Exit from the loop with the given exit code.

Parameters:rc (int) –

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static GetActive()

Return the currently active (running) event loop.

May return None if there is no active event loop (e.g. during application startup or shutdown).

Return type: EventLoopBase

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IsEventAllowedInsideYield(self, cat)

Returns True if the given event category is allowed inside a YieldFor call (i.e.

compares the given category against the last mask passed to YieldFor ).

Parameters:cat (EventCategory) – Return type:bool

See also

Event.GetEventCategory

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IsMain(self)

Returns True if this is the main loop executed by App.OnRun .

Return type:bool

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IsOk(self)

Use this to check whether the event loop was successfully created before using it.

Return type:bool

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IsRunning(self)

Return True if this event loop is currently running.

Notice that even if this event loop hasn’t terminated yet but has just spawned a nested (e.g. modal) event loop, this method would return False.

Return type:bool

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IsYielding(self)

Returns True if called from inside Yield or from inside YieldFor .

Return type:bool

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Pending(self)

Return True if any events are available.

If this method returns True, calling Dispatch will not block.

Return type:bool

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ProcessIdle(self)

This virtual function is called when the application becomes idle and normally just sends IdleEvent to all interested parties.

It should return True if more idle events are needed, False if not.

Return type:bool

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Run(self)

Start the event loop, return the exit code when it is finished.

Logically, this method calls Dispatch in a loop until it returns False and also takes care of generating idle events during each loop iteration. However not all implementations of this class really implement it like this (e.g. wxGTK does not) so you shouldn’t rely on Dispatch being called from inside this function.

Return type:int Returns:The argument passed to Exit which terminated this event loop.

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static SetActive(loop)

Set currently active (running) event loop.

Called by EventLoopActivator, use an instance of this class instead of calling this method directly to ensure that the previously active event loop is restored.

Results in a call to AppConsole.OnEventLoopEnter .

Parameters:loop (EventLoopBase) –

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WakeUp(self)

Called by wxWidgets to wake up the event loop even if it is currently blocked inside Dispatch .

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WakeUpIdle(self)

Makes sure that idle events are sent again.

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Yield(self, 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. You can avoid unwanted reentrancies also using IsYielding .

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.FlushActive .

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.

Parameters:onlyIfNeeded (bool) – Return type:bool

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YieldFor(self, eventsToProcess)

Works like Yield with onlyIfNeeded == True, except that it allows the caller to specify a mask of the EventCategory values which indicates which events should be processed and which should instead be “delayed” (i.e.

processed by the main loop later).

Note that this is a safer alternative to Yield since it ensures that only the events you’re interested to will be processed; i.e. this method helps to avoid unwanted reentrancies.

Note that currently only wxMSW and wxGTK do support selective yield of native events coming from the underlying GUI toolkit. wxWidgets events posted using EvtHandler.AddPendingEvent or EvtHandler.QueueEvent are instead selectively processed by all ports.

Parameters:eventsToProcess (long) – Return type:bool

See also

Event.GetEventCategory