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EZ_ItemAddDnDDataDecoder(3)	EZWGL Functions	   EZ_ItemAddDnDDataDecoder(3)

NAME
       EZ_ItemAddDnDDataDecoder,EZ_ItemAddDnDDataEncoder,    EZ_ItemDeleteDnD-
       DataDecoder,   EZ_ItemDeleteDnDDataEncoder   EZ_ItemDeleteAllDnDDataDe-
       coders,	EZ_ItemDeleteAllDnDDataEncoders	 -  register/remove  drag  and
       drop(DnD) handlers

SYNOPSIS
       #include	<EZ.h>

       void  EZ_ItemAddDnDDataDecoder(EZ_Item *item, Atom atom,
		unsigned int tag, EZ_DnDDecoder	decoder, void *ddata,
		EZ_CallBack dcallback, void *cdata)

       void  EZ_ItemAddDnDDataEncoder(EZ_Item *item, Atom atom,
		unsigned int tag, EZ_DnDEncoder	encoder, void *edata,
		EZ_CallBack ecallback, void *cdata)

       void  EZ_ItemDelteDnDDataDecoder(EZ_Item	*item,
		EZ_DnDDecoder decoder, void *ddata)

       void  EZ_ItemDelteDnDDataEncoder(EZ_Item	*item,
		EZ_DnDEncoder encoder, void *edata)

       void  EZ_ItemDelteAllDnDDataDecoders(EZ_Item *item)

       void  EZ_ItemDelteAllDnDDataEncoders(EZ_Item *item)

ARGUMENTS
       atom Specifies a	DnD target.

       tag Specifies a tag. It must be either ~0 or a value or'ed  from	 Shif-
       Mask, ControlMask and Mod1Mask.

       item Specifies a	display	item.

       encoder Specify a DnD data encoder.

       decoder Specify a DnD data decoder.

       edata Specify a client data to be passed	to encoder when	invoked.

       ddata Specify a client data to be passed	to decoder when	invoked.

       ecallback  Specify a procedure to be invoked when encoder executes suc-
       cesfully.

       dcallback Specify a procedure to	be invoked when	decoder	executes  suc-
       cesfully.

       dcallback when called.

DESCRIPTION
       EZ_ItemAddDnDDataEncoder	  registers a DnD encoder to a display item. A
       EZ_DnDEncoder is	a data conversion procedure of the type
	int (*encoder)(void *object, void *data, char **message,int *length, int *needfree)

       EZ_ItemDeleteDnDDataEncoder  dissociate a DnD encoder  with  a  display
       item.  The specified decoder will be removed only if both the procedure
       and client data match.

       EZ_ItemDeleteAllDnDDataEncoders removes all DnD encoders	registered  to
       a display item.

       EZ_ItemAddDnDDataDecoder	  registers a DnD decoder to a item. A EZ_DnD-
       Decoder is a data conversion procedure of the type
	 int (*decoder)(void *object, void *data, char *message, int length)

       EZ_ItemDeleteDnDDataDecoder  dissociate a DnD decoder  with  a  display
       item.  The specified decoder will be removed only if both the procedure
       and client data match.

       EZ_ItemDeleteAllDnDDataDecoders removes all DnD decoders	registered  to
       a display item.

       The tag argument	is used	to choose conversion methods. It is useful for
       the following situations.

       1. A drag source	has multiple encoders for the same conversion  target.
       For  example,  when  transfering	 files,	 one may want either to	copy a
       file or move a file to the destination specified	by the drop site. This
       can  be	achieved by registering	multiple encoders with different tags.
       For example, shift-press-drag-relase for	copying	the  file  and	cntrl-
       press-drag-release for moving the file.

       2.  Sometimes  it  is preferable	to enforce a more strict drag and drop
       policy so that a	careless drag and drop will not	do any harm.  For  ex-
       ample, if you write a file manager and want to use DnD to remove	files,
       it may be better	to enforce a control-press-drag-release	policy for the
       trash can.

       The  tag	 value	~0 is reserved for a special purpose: drop at the root
       window of your display. Strictly	speaking, the root  window  is	not  a
       valid drop site because it does not talk	to the drag source.  Neverthe-
       less, for applications like file	managers, it is	useful to have a  fea-
       ture  so	 a  user  can drop an item at the root window.	Since the root
       window is not an	official drop site, there will be no  data  transfers.
       The action is completely	handled	by the drag source. If you want	to use
       this feature. Here are the tricks.

	  1. Write a special encoder which  does  not  convert	anything,  but
	  rather,  acts	like a callback. In the	example	of droping a file item
	  over the background, you may want to create a	Icon widget, set it up
	  properly and display it. The encoder has to return EZ_DND_SUCCESS on
	  success and EZ_DND_FAILURE on	failure.  The callbacks	for this  spe-
	  cial	encoder	 behave	exactly	the same as that of a regular encoder.
	  It is	invoked	when the encoder returns EZ_DND_SUCCESS+.

	  2. Register your special encoder with	a tag value ~0.

EXAMPLES
       Atom MY_FILE_NAME_ATOM;	    /* conversion type */
       Atom MY_FILE_CONTENTS_ATOM;

       int encodeFileName(EZ_Item *item, void *data,
			  char **message, /* place to return the data after conversion */
			  int  *length,	  /* return the	length of message */
			  int *needFree)  /* signal whether to free *message when done */
       {
	 if(item)
	   {
	     /*	file name is stored in the client data slots of	item */
	     char *ptr = (char *)EZ_GetItemPtrData(item);
	     int  len =	EZ_GetItemIntData(item);
	     if(len > 0)
	       {
		 *length = len;
		 *message = ptr;
		 *needFree = 0;
		 return(EZ_DND_SUCCESS);
	       }
	   }
	 return(EZ_DND_FAILURE);
       }

       int encodeFileContents(EZ_Item *item, void *data,
			      char **message, int *length, int *needFree)
       {
	 if(item)
	   {
	     char *ptr = (char *)EZ_GetItemPtrData(item);
	     int  len =	EZ_GetItemIntData(item);
	     if(len > 0)
	       {
		 char *msg;
		 int  c, totalLength = 0;
		 FILE *fp = fopen(ptr, "r");
		 if(fp)	while(fgetc(fp)	!= EOF)	totalLength++; /* length of file */
		 (void)rewind(fp);
		 msg = (char *)malloc( (totalLength + 1)*sizeof(char));
		 ptr = msg;
		 while((c = fgetc(fp)) != EOF) *ptr++ =c;
		 fclose(fp);
		*length	= totalLength;
		*message = msg;
		*needFree = 1;	/* ask EZWGL to	free msg when done with	it */
		return(EZ_DND_SUCCESS);
	       }
	   }
	 return(EZ_DND_FAILURE);
       }

       int decodeFileName(EZ_Item *item, void *data,
		    char *message, int length)
       {
	 if(item)
	   {
	     if(length > 0)
	    {
	      FILE *fp = fopen(message,	"r");
	      if(fp)
		{
		  int c;
		  while( (c = getc(fp))	!= EOF)	putchar(c);
		  fclose(fp);
		  return(EZ_DND_SUCCESS);
		}
	    }
	   }
	 return(EZ_DND_FAILURE);
       }

       int decodeFileContents(EZ_Item *item, void *data,
			char *message, int length)
       {
	 if(item)
	   {
	     if(length > 0)
	    {
	      printf("%s", message);
	      return(EZ_DND_SUCCESS);
	    }
	   }
	 return(EZ_DND_FAILURE);
       }

SEE ALSO
       EZ_ItemAddDnDDataDecoder(3),EZ_ItemAddDnDDataEncoder(3)

EZWGL						   EZ_ItemAddDnDDataDecoder(3)

NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | EXAMPLES | SEE ALSO

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