DOKK / manpages / debian 10 / tk8.6-doc / Tk_DeleteSelHandler.3tk.en
Tk_CreateSelHandler(3tk) Tk Library Procedures Tk_CreateSelHandler(3tk) 







Tk_CreateSelHandler, Tk_DeleteSelHandler - arrange to handle
    requests for a selection








#include <tk.h>

Tk_CreateSelHandler(tkwin, selection, target, proc, clientData, format)

Tk_DeleteSelHandler(tkwin, selection, target)









  
Tk_Window tkwin (in)

  
Window for which proc will provide selection information.

  
Atom selection (in)

  
The name of the selection for which proc will provide selection
      information.

  
Atom target (in)

  
Form in which proc can provide the selection (e.g. STRING or
      FILE_NAME). Corresponds to type arguments in selection
      commands.

  
Tk_SelectionProc *proc (in)

  
Procedure to invoke whenever the selection is owned by tkwin and
      the selection contents are requested in the format given by
    target.

  
ClientData clientData (in)

  
Arbitrary one-word value to pass to proc.

  
Atom format (in)

  
If the selection requestor is not in this process, format
      determines the representation used to transmit the selection to its
      requestor.
    
    

    

  










Tk_CreateSelHandler arranges for a particular procedure
    (proc) to be called whenever selection is owned by
    tkwin and the selection contents are requested in the form given by
    target. Target should be one of the entries defined in the
    left column of Table 2 of the X Inter-Client Communication Conventions
    Manual (ICCCM) or any other form in which an application is willing to
    present the selection. The most common form is STRING.


Proc should have arguments and result that match the type
    Tk_SelectionProc:




typedef int Tk_SelectionProc(


        ClientData clientData,


        int offset,


        char *buffer,


        int maxBytes);



The clientData parameter to proc is a copy of the
  clientData argument given to Tk_CreateSelHandler. Typically,
  clientData points to a data structure containing application-specific
  information that is needed to retrieve the selection. Offset specifies
  an offset position into the selection, buffer specifies a location at
  which to copy information about the selection, and maxBytes specifies
  the amount of space available at buffer. Proc should place a
  NULL-terminated string at buffer containing maxBytes or fewer
  characters (not including the terminating NULL), and it should return a count
  of the number of non-NULL characters stored at buffer. If the selection
  no longer exists (e.g. it once existed but the user deleted the range of
  characters containing it), then proc should return -1.

When transferring large selections, Tk will break them up into
    smaller pieces (typically a few thousand bytes each) for more efficient
    transmission. It will do this by calling proc one or more times,
    using successively higher values of offset to retrieve successive
    portions of the selection. If proc returns a count less than
    maxBytes it means that the entire remainder of the selection has been
    returned. If proc's return value is maxBytes it means there
    may be additional information in the selection, so Tk must make another call
    to proc to retrieve the next portion.


Proc always returns selection information in the form of a
    character string. However, the ICCCM allows for information to be
    transmitted from the selection owner to the selection requestor in any of
    several formats, such as a string, an array of atoms, an array of integers,
    etc. The format argument to Tk_CreateSelHandler indicates what
    format should be used to transmit the selection to its requestor (see the
    middle column of Table 2 of the ICCCM for examples). If format is not
    STRING, then Tk will take the value returned by proc and divided it
    into fields separated by white space. If format is ATOM, then Tk will
    return the selection as an array of atoms, with each field in proc's
    result treated as the name of one atom. For any other value of
    format, Tk will return the selection as an array of 32-bit values
    where each field of proc's result is treated as a number and
    translated to a 32-bit value. In any event, the format atom is
    returned to the selection requestor along with the contents of the
    selection.


If Tk_CreateSelHandler is called when there already exists
    a handler for selection and target on tkwin, then the
    existing handler is replaced with a new one.


Tk_DeleteSelHandler removes the handler given by
    tkwin, selection, and target, if such a handler exists.
    If there is no such handler then it has no effect.








format, handler, selection, target







  

    4.0
    Tk