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tk_restrictevents(3) [osx man page]

Tk_RestrictEvents(3)					       Tk Library Procedures					      Tk_RestrictEvents(3)


Tk_RestrictEvents - filter and selectively delay X events SYNOPSIS
#include <tk.h> Tk_RestrictProc * Tk_RestrictEvents(proc, clientData, prevClientDataPtr) ARGUMENTS
Tk_RestrictProc *proc (in) Predicate procedure to call to filter incoming X events. NULL means do not restrict events at all. ClientData clientData (in) Arbitrary argument to pass to proc. ClientData *prevClientDataPtr (out) Pointer to place to save argument to previous restrict procedure. _________________________________________________________________ DESCRIPTION
This procedure is useful in certain situations where applications are only prepared to receive certain X events. After Tk_RestrictEvents is called, Tk_DoOneEvent (and hence Tk_MainLoop) will filter X input events through proc. Proc indicates whether a given event is to be processed immediately, deferred until some later time (e.g. when the event restriction is lifted), or discarded. Proc is a procedure with arguments and result that match the type Tk_RestrictProc: typedef Tk_RestrictAction Tk_RestrictProc( ClientData clientData, XEvent *eventPtr); The clientData argument is a copy of the clientData passed to Tk_RestrictEvents; it may be used to provide proc with information it needs to filter events. The eventPtr points to an event under consideration. Proc returns a restrict action (enumerated type Tk_RestrictAction) that indicates what Tk_DoOneEvent should do with the event. If the return value is TK_PROCESS_EVENT, then the event will be handled imme- diately. If the return value is TK_DEFER_EVENT, then the event will be left on the event queue for later processing. If the return value is TK_DISCARD_EVENT, then the event will be removed from the event queue and discarded without being processed. Tk_RestrictEvents uses its return value and prevClientDataPtr to return information about the current event restriction procedure (a NULL return value means there are currently no restrictions). These values may be used to restore the previous restriction state when there is no longer any need for the current restriction. There are very few places where Tk_RestrictEvents is needed. In most cases, the best way to restrict events is by changing the bindings with the bind Tcl command or by calling Tk_CreateEventHandler and Tk_DeleteEventHandler from C. The main place where Tk_RestrictEvents must be used is when performing synchronous actions (for example, if you need to wait for a particular event to occur on a particular win- dow but you do not want to invoke any handlers for any other events). The "obvious" solution in these situations is to call XNextEvent or XWindowEvent, but these procedures cannot be used because Tk keeps its own event queue that is separate from the X event queue. Instead, call Tk_RestrictEvents to set up a filter, then call Tk_DoOneEvent to retrieve the desired event(s). KEYWORDS
delay, event, filter, restriction Tk Tk_RestrictEvents(3)

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Tk_CreateEventHandler(3)				       Tk Library Procedures					  Tk_CreateEventHandler(3)


Tk_CreateEventHandler, Tk_DeleteEventHandler - associate procedure callback with an X event SYNOPSIS
#include <tk.h> Tk_CreateEventHandler(tkwin, mask, proc, clientData) Tk_DeleteEventHandler(tkwin, mask, proc, clientData) ARGUMENTS
Tk_Window tkwin (in) Token for window in which events may occur. unsigned long mask (in) Bit-mask of events (such as ButtonPressMask) for which proc should be called. Tk_EventProc *proc (in) Procedure to invoke whenever an event in mask occurs in the window given by tkwin. ClientData clientData (in) Arbitrary one-word value to pass to proc. _________________________________________________________________ DESCRIPTION
Tk_CreateEventHandler arranges for proc to be invoked in the future whenever one of the event types specified by mask occurs in the window specified by tkwin. The callback to proc will be made by Tk_HandleEvent; this mechanism only works in programs that dispatch events through Tk_HandleEvent (or through other Tk procedures that call Tk_HandleEvent, such as Tk_DoOneEvent or Tk_MainLoop). Proc should have arguments and result that match the type Tk_EventProc: typedef void Tk_EventProc( ClientData clientData, XEvent *eventPtr); The clientData parameter to proc is a copy of the clientData argument given to Tk_CreateEventHandler when the callback was created. Typi- cally, clientData points to a data structure containing application-specific information about the window in which the event occurred. EventPtr is a pointer to the X event, which will be one of the ones specified in the mask argument to Tk_CreateEventHandler. Tk_DeleteEventHandler may be called to delete a previously-created event handler: it deletes the first handler it finds that is associated with tkwin and matches the mask, proc, and clientData arguments. If no such handler exists, then Tk_HandleEvent returns without doing any- thing. Although Tk supports it, it's probably a bad idea to have more than one callback with the same mask, proc, and clientData argu- ments. When a window is deleted all of its handlers will be deleted automatically; in this case there is no need to call Tk_DeleteEven- tHandler. If multiple handlers are declared for the same type of X event on the same window, then the handlers will be invoked in the order they were created. KEYWORDS
bind, callback, event, handler Tk Tk_CreateEventHandler(3)
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