gtk- Binding to the Gtk+ graphical user interface library.

Portabilityportable (depends on GHC)
Safe HaskellNone




Types and accessors to examine information in events.



This modules provides a monad that encapsulates the information in an event.

The events a widget can receive are defined in Graphics.UI.Gtk.Abstract.Widget. Every event carries additional information which is accessible through functions in the EventM monad. For instance, every event is associated with a DrawWindow which is accessed using the eventWindow accessor function. Other information is only available in one specific event. For example, the area that has to be redrawn, accessed by eventArea is only available in the exposeEvent. Indeed, you can only call eventArea if the first type parameter of EventM is the phantom type EExpose. (A phantom type is a type for which no values exist and which is only used to enforce certain constraints on the usage of functions such as eventArea.) Some information is available in several but not all events. In order to express these constraints the module defines type classes whose names start with Has... but which are not exported, implying that no new instance can be created. (They could be called phantom type classes.) For instance, the mouse pointer coordinates can be retrieved using the function eventCoordinates which requires that the first type parameter of EventM is in the class HasCoordinates. The module supplies instance of class HasCoordinates for the types EButton, ECrossing, EMotion and EScroll. Thus for all events that require an EventM action with one of the types above, the accessor function eventCoordinates may be used.

Note that an event handler must always returns True if the event was handled or False if the event should be dealt with by another event handler. For instance, a handler for a key press should return False if the pressed key is not one of those that the widget reacts to. In this case the event is passed to the parent widgets. This ensures that pressing, say, Alt-F opens the file menu even if the current input focus is in a text entry widget. In order to facilitate writing handlers that may abort handling an event, this module provides the function tryEvent. This function catches pattern match exceptions and returns False. If the signal successfully runs to its end, it returns True. A typical use is as follows:

 widget `on` keyPressEvent $ tryEvent $ do
   [Control] <- eventModifier
   "Return" <- eventKeyName
   liftIO $ putStrLn "Ctrl-Return pressed"

The rationale is that the action will throw an exception if the two event functions eventModifier and eventKeyName return something else than what is stated in the pattern. When no exception is thrown, execution continues to the last statement where the event is processed, here we merely print a message. Note that the return value of this statement must be () since tryEvent always assumes that the function handeled the event if no exception is thrown. A handler wrapped by tryEvent can also indicate that it cannot handle the given event by calling stopEvent.

Finally, not that the EventM monad wraps the IO monad. As such you can (and usually have to) use liftIO to execute IO functions.

Event monad and type tags

type EventM t a = ReaderT (Ptr t) IO aSource

A monad providing access to data in an event.

data EAny Source

A tag for events that do not carry any event-specific information.

data EKey Source

A tag for key events.

data EButton Source

A tag for Button events.

data EScroll Source

A tag for Scroll events.

data EMotion Source

A tag for Motion events.

data EExpose Source

A tag for Expose events.

data EVisibility Source

A tag for Visibility events.

data ECrossing Source

A tag for Crossing events.

data EFocus Source

A tag for Focus events.

data EConfigure Source

A tag for Configure events.

data EProperty Source

A tag for Property events.

data EProximity Source

A tag for Proximity events.

data EWindowState Source

A tag for WindowState event.

data EOwnerChange Source

A tag for OwnerChange events.

data EGrabBroken Source

A tag for GrabBroken events.

Accessor functions for event information

eventWindow :: EventM any DrawWindowSource

Retrieve the DrawWindow that this event relates to.

eventSent :: EventM any BoolSource

Query if this event was sent sent explicitly by the application (rather than being generated by human interaction).

eventCoordinates :: HasCoordinates t => EventM t (Double, Double)Source

Retrieve the (x,y) coordinates of the mouse.

eventRootCoordinates :: HasRootCoordinates t => EventM t (Double, Double)Source

Retrieve the (x,y) coordinates of the mouse relative to the root (origin) of the screen.

eventModifier :: HasModifier t => EventM t [Modifier]Source

Query the modifier keys that were depressed when the event happened. Sticky modifiers such as CapsLock are omitted in the return value. Use eventModifierAll your application requires all modifiers. Use eventModifierMouse if you just need the mouse buttons.

eventModifierAll :: HasModifier t => EventM t [Modifier]Source

Query the modifier keys that were depressed when the event happened. The result includes sticky modifiers such as CapsLock. Normally, eventModifier is more appropriate in applications.

eventModifierMouse :: HasModifier t => EventM t [Modifier]Source

Query the mouse buttons that were depressed when the event happened.

eventTime :: HasTime t => EventM t TimeStampSource

Query the time when the event occurred.

eventKeyVal :: EventM EKey KeyValSource

The key value. See KeyVal.

eventKeyName :: EventM EKey StringSource

The key value as a string. See KeyVal.

eventHardwareKeycode :: EventM EKey KeyCodeSource

The hardware key code.

eventKeyboardGroup :: EventM EKey Word8Source

The keyboard group.

eventButton :: EventM EButton MouseButtonSource

Query the mouse buttons.

data Click Source

Type of mouse click


data ScrollDirection Source

in which direction was scrolled?

eventScrollDirection :: EventM EScroll ScrollDirectionSource

Query the direction of scrolling.

eventIsHint :: EventM EMotion BoolSource

Check if the motion event is only a hint rather than the full mouse movement information.

eventRequestMotions :: EventM EMotion ()Source

Request more motion notifies if this event is a motion notify hint event.

This action should be used instead of drawWindowGetPointer to request further motion notifies, because it also works for extension events where motion notifies are provided for devices other than the core pointer.

Coordinate extraction, processing and requesting more motion events from a motionNotifyEvent usually works like this:

 on widget motionNotifyEvent $ do
   (x, y) <- eventCoordinates
   -- handle the x,y motion:
   -- finally, notify that we are ready to get more motion events:

eventArea :: EventM EExpose RectangleSource

Query a bounding box of the region that needs to be updated.

eventRegion :: EventM EExpose RegionSource

Query the region that needs to be updated. Removed in Gtk3.

eventVisibilityState :: EventM EVisibility VisibilityStateSource

Get the visibility status of a window.

eventCrossingMode :: EventM ECrossing CrossingModeSource

Get the mode of the mouse cursor crossing a window.

data NotifyType Source

Information on from what level of the widget hierarchy the mouse cursor came.

The window is entered from an ancestor or left towards an ancestor.
The pointer moves between an ancestor and an inferior of the window.
The window is entered from an inferior or left towards an inferior.
The window is entered from or left towards a window which is neither an ancestor nor an inferior.
The pointer moves between two windows which are not ancestors of each other and the window is part of the ancestor chain between one of these windows and their least common ancestor.
The level change does not fit into any of the other categories or could not be determined.

eventNotifyType :: EventM ECrossing NotifyTypeSource

Get the notify type of the mouse cursor crossing a window.

eventCrossingFocus :: EventM ECrossing BoolSource

Query if the window has the focus or is an inferior window.

eventFocusIn :: EventM EFocus BoolSource

Query if a window gained focus (True) or lost the focus (False).

eventPosition :: EventM EConfigure (Int, Int)Source

Get the (x,y) position of the window within the parent window.

eventSize :: EventM EConfigure (Int, Int)Source

Get the new size of the window as (width,height).

data WindowState Source

The state a DrawWindow is in.


Bounded WindowState 
Enum WindowState

These are hints for the window manager that indicate what type of function the window has. The window manager can use this when determining decoration and behaviour of the window. The hint must be set before mapping the window.

See the extended window manager hints specification for more details about window types.

Eq WindowState 
Show WindowState 
Flags WindowState 

eventWindowStateChanged :: EventM EWindowState [WindowState]Source

Query which window state bits have changed.

eventWindowState :: EventM EWindowState [WindowState]Source

Query the new window state.

eventChangeReason :: EventM EOwnerChange OwnerChangeSource

Query why a seleciton changed its owner.

eventSelection :: EventM EOwnerChange SelectionTagSource

Query what selection changed its owner.

eventSelectionTime :: EventM EOwnerChange TimeStampSource

Query the time when the selection was taken over.

eventKeyboardGrab :: EventM EGrabBroken BoolSource

Check if a keyboard (True) or a mouse pointer grap (False) was broken.

eventImplicit :: EventM EGrabBroken BoolSource

Check if a grab was broken implicitly.

eventGrabWindow :: EventM EGrabBroken (Maybe DrawWindow)Source

Get the new window that owns the grab or Nothing if the window is not part of this application.

Auxilliary Definitions

data Modifier Source

Keyboard modifiers that are depressed when the user presses a key or a mouse button.

  • This data type is used to build lists of modifers that were active during an event.
  • The Apple key on Macintoshs is mapped to Alt2 and the Meta key (if available).
  • Since Gtk 2.10, there are also Super, Hyper and Meta modifiers which are simply generated from Alt .. Compose modifier keys, depending on the mapping used by the windowing system. Due to one key being mapped to e.g. Alt2 and Meta, you shouldn't pattern match directly against a certain key but check whether a key is in the list using the elem function, say.

type TimeStamp = Word32Source

The time (in milliseconds) when an event happened. This is used mostly for ordering events and responses to events.

currentTime :: TimeStampSource

Represents the current time, and can be used anywhere a time is expected.

tryEvent :: EventM any () -> EventM any BoolSource

Execute an event handler and assume it handled the event unless it threw a pattern match exception or calls mzero (e.g. via guard).

stopEvent :: EventM any ()Source

Explicitly stop the handling of an event. This function should only be called inside a handler that is wrapped with tryEvent. (It merely throws a bogus pattern matching error which tryEvent interprets as if the handler does not handle the event.)