drag&drop(n) BLT Built-In Commands drag&drop(n)______________________________________________________________________________NAME
drag&drop - facilities for handling drag&drop data transfers
SYNOPSIS
drag&drop source
drag&drop source window ?options?
drag&drop source window handler ?dataType? ?command arg arg...?
drag&drop target
drag&drop target window handler ?dataType command arg arg...?
drag&drop target window handle dataType ?value?
drag&drop token window
drag&drop drag window x y
drag&drop drop window x y
drag&drop active
drag&drop errors ?proc?
drag&drop location ?x y?
_________________________________________________________________DESCRIPTION
The drag&drop command provides access to a set of facilities for manag‐
ing drag-and-drop data transfers. Any of the usual Tk widgets can be
registered to participate in the drag-and-drop process. Widgets regis‐
tered as a drag&drop source can export data to other widgets registered
as a drag&drop target. Note that a particular widget can be registered
as a source, as a target, or as both.
The drag-and-drop process begins when the user clicks and holds a mouse
button in a source window; a token window appears with an icon or mes‐
sage to represent the data being transferred. As the user moves the
mouse pointer, the token window follows along, acting as a movable
packet of data. Whenever the mouse pointer falls on a valid target
window, the border of the token window is changed to a raised (active)
state. When the mouse button is released over the target window, a Tcl
routine is invoked to send the data to the desired application, and the
target window is asked to "handle" the data. If this communication
process fails, a rejection symbol (a circle with a line through it) is
displayed on the token window to indicate failure.
The details of the communication process are fully configurable by the
application developer. In the simplest case, the value that is sent to
the target window is a simple string. The target window is simply
asked to "handle" that string value. In general, the source window can
have a special "handler" procedure to transfer a particular data type
by issuing a series of "send" commands. After this, the target window
is again asked to "handle" the result.
Both sources and targets can have a list of "handlers" for different
data types. As a token window is dragged from its source to various
targets, each target is checked to see if it recognizes a handler
offered by the source. If it does, it is treated as a valid target.
Otherwise, it is ignored. This scheme allows the same source to inter‐
act with many different kinds of targets. For example, a source for
RGB color samples might have "color" and "string" handlers. This would
allow it to communicate with "color" targets (sending RGB data) as well
as entry widgets (sending strings of the form "#rrggbb").
This introduction was presented as a brief overview of the communica‐
tion process; further details are presented below:
drag&drop source
Returns a list of path names for widgets registered as drag&drop
sources. Returns an empty string if no widgets have been regis‐
tered.
drag&drop source window ?options?
Registers a new drag&drop source window with the given options,
or modifies the options for an existing window:
Name: buttonBinding
Class: ButtonBinding
Switch: -button n
Specifies the mouse button (integer 1-5) that will invoke
the drag&drop operation on the source window. This
causes the following bindings to be added to the widget:
bind win <ButtonPress-n> {drag&drop drag %W %X %Y}
bind win <Bn-Motion> {drag&drop drag %W %X %Y}
bind win <ButtonRelease-n> {drag&drop drop %W %X %Y}
The default value is button 3. If the value "0" is specified,
then no bindings are added; this enables the user to establish
bindings manually.
Name: packageCommand
Class: Command
Switch: -packagecmd command
Specifies a Tcl command used to establish the appearance
of the token window at the start of each drag&drop opera‐
tion. This command is automatically invoked by the
drag&drop drag command whenever the token window is about
to be mapped for a drag operation. It should update the
appearance of the token window to represent the data that
is being moved.
The following substitutions are made in the command string
before it is executed:
%t Replaced with the window path name for the token
which represents the data being dragged.
%W Replaced with the window path name for the
drag&drop source.
The return value from the package command represents the data
being transferred. If the package command returns an empty
string, the drag operation is quietly aborted. This can be used
to disallow drag&drop operations from certain parts of a widget,
if the drag position is inappropriate.
For example, the following package routine will select an item
from a listbox and configure the token window to display the
selected string. It uses the drag&drop location command to
determine the entry in the listbox that the user has selected
and it returns this as the data value:
proc package_list_item {lbox token} {
set xy [drag&drop location]
set y [expr [lindex $xy 1]-[winfo rooty $lbox]]
set str [$lbox get [$lbox nearest $y]]
$token.value configure -text $str
return $str
}
The return value is available later when the source and target
communicate. If the source has a command associated with its
data handler, then this value is substituted in place of "%v" in
the source handler. Otherwise, it is substituted in place of
"%v" in the target handler.
Name: rejectBackground
Class: Background
Switch: -rejectbg color
Specifies the color used to draw the background of the
rejection symbol on the token window. The rejection sym‐
bol (a circle with a line through it--the international
"no") appears whenever communication fails.
Name: rejectForeground
Class: Foreground
Switch: -rejectfg color
Specifies the color used to draw the foreground of the
rejection symbol on the token window.
Name: rejectStipple
Class: Stipple
Switch: -rejectstipple pattern
Specifies a stipple pattern used to draw the foreground
of the rejection symbol on the token window. Any of the
forms acceptable to Tk_GetBitmap can be used.
Name: selfTarget
Class: SelfTarget
Switch: -selftarget boolean
If the boolean value is true, and if a source widget is
also registered as a compatible target, then the source
will be able to transmit to itself during drag&drop oper‐
ations. This is primarily useful for complex sources
such as a canvas widget, where items may be moved from
place to place within the same widget. By default, this
option is disabled.
Name: send
Class: Send
Switch: -send list
Specifies a list of dataTypes enabled for communication.
Only dataTypes defined by commands of the form "drag&drop
source window handler ?dataType ?command arg arg...?" are
allowed. This list also determines the priority of the
various dataTypes. When a token window is over a poten‐
tial drag&drop target, this list is searched from start
to finish for a dataType that is also recognized by the
target. The first matching dataType found determines the
value that will be sent if the token is dropped. If no
matching dataType is found, then the target is incompati‐
ble, and is ignored. By default, this option has the
value "all", indicating that all dataTypes should be con‐
sidered in the order that they were defined for the
source.
Note that this option makes it easy to control a drag&drop
source. Setting the value to an empty string disables the
source; setting the value back to "all" restores communication.
Name: siteCommand
Class: Command
Switch: -sitecmd command
Specifies a Tcl command used to update the appearance of
the token window. If specified, this command is automat‐
ically invoked by the drag&drop drag command whenever the
token window is over a compatible drag&drop target.
The following substitutions are made in the command string
before it is executed:
%s Replaced with "1" if the token window is over a
compatible target, and "0" otherwise.
%t Replaced with the window path name for the token
which represents the data being dragged.
Regardless of this command, border of the token window will
become raised whenever the token is over a valid target. This
command can be used to display other visual cues.
Name: tokenAnchor
Class: Anchor
Switch: -tokenanchor anchor
Specifies how the token window is positioned relative to
the mouse pointer coordinates passed to the drag&drop
drag command. Must be one of the values n, s, e, w, cen‐
ter, nw, ne, sw or se. For example, "nw" means to posi‐
tion the token such that its upper-left corner is at the
mouse pointer. The default value is "center".
Name: tokenBackground
Class: Background
Switch: -tokenbg color
Specifies the color used to draw the background of the
token window.
Name: tokenBorderWidth
Class: BorderWidth
Switch: -tokenborderwidth size
Specifies the width in pixels of the border around the
token window. This border becomes raised to indicate
when the token is over a compatible drag&drop target
site. The value may have any of the forms acceptable to
Tk_GetPixels. The default value is "3".
Name: tokenCursor
Class: Cursor
Switch: -tokencursor cursor
Specifies the cursor used when a token window is active.
The value may have any of the forms acceptable to
Tk_GetCursor. The default value is "center_ptr".
drag&drop source window handler ?dataType? ?command arg arg...?
With no extra arguments, this command returns a list of all
dataType names that have been registered for the source window.
If only the dataType is specified, then the dataType is created
if necessary, and the command associated with the dataType is
returned. Otherwise, it concatenates the command and any extra
arg strings, and registers a new dataType with this command.
The following substitutions are made in the command string before it is
executed:
%i Replaced with the name of the interpreter for the target
application.
%v Replaced with the value returned from the "-packagecmd"
command.
%w Replaced with the window path name for the target window.
A typical source handler contains one or more "send" commands which
transfer data to the remote application. The target window is then
asked to handle the new data. Whatever value is returned by the source
command handler is automatically substituted into the "%v" fields of
the target handler.
This separation between the transfer and the handling of the data is
important. It allows the same source handler to transfer data for many
different targets, and it allows each of the targets to handle the
incoming data differently. If an error is encountered during the com‐
munication process, the rejection symbol is posted on the token window
to indicate failure.
drag&drop target
Returns a list of path names for widgets registered as drag&drop
targets. Returns an empty string if no widgets have been regis‐
tered.
drag&drop target window handler ?dataType command arg arg...?
Registers a new drag&drop target window with a given handler, or
modifies the handlers for an existing window. If no dataType is
specified, this command returns the current list of recognized
dataType strings. Each dataType is a symbolic name representing
a form of data, and the corresponding command is a Tcl command
that specifies how the target will make use of the data. This
command is invoked indirectly after a source has transferred
data to a target application.
The following substitutions are made in the command string before it is
executed:
%v In the simplest case, the source window does not have a
handler command for the selected dataType, and this field
is replaced with the result from the "-packagecmd" com‐
mand. When the source does have a handler command, the
result from the "-packagecmd" command is substituted into
its "%v" field, and the result from this command is sub‐
stituted into this field in the target command.
%W Replaced with the window path name for the target window.
drag&drop target window handle dataType ?value?
Searches for the given dataType name among the handlers regis‐
tered for the target window, and invokes the appropriate com‐
mand. If a value is specified, it is substituted into any "%v"
fields in the handler command associated with the dataType. If
the dataType name is not recognized, this command returns an
error. This command is invoked automatically by the drag&drop
facility when data is being transferred from a source to a tar‐
get.
drag&drop token window
Returns the token window associated with a drag&drop source win‐
dow. The token window is used to represent data as it is being
dragged from the source to a target. When a source is first
established, its token window must be filled with widgets to
display the source data. For example,
drag&drop source .foo
set win [drag&drop token .foo]
label $win.label -text "Data"
pack $win.label
drag&drop drag window x y
Marks the start of (or movement during) a drag&drop operation.
If the token window is unmapped when this command is invoked,
then the -packagecmd for the source window is executed. If this
command is successful and returns a non-null string, the token
window is mapped. On subsequent calls, the token window is
moved to the new x y location. Unless the "-button 0" option is
specified for the source, this command is automatically bound to
<ButtonPress-n> and <Bn-Motion> events for "-button n" of the
source widget.
drag&drop drop window x y
Marks the end of a drag&drop operation. If the mouse pointer is
over a compatible target window, then the appropriate send han‐
dler for the first compatible dataType is invoked to handle the
data transfer. If the data transfer is successful, then the
token window is unmapped; otherwise, a rejection symbol is drawn
on the token window, and the window is unmapped after a small
delay. Unless the "-button 0" option is specified for the
source, this command is automatically bound to the <ButtonRe‐
lease-n> event for "-button n" of the source widget.
drag&drop active
Returns "1" if a drag&drop operation is in progress, and "0"
otherwise. A drag&drop operation officially starts after the
package command has been executed successfully, and ends after
the send handler has been executed (successfully or otherwise).
drag&drop errors ?proc?
Specifies a Tcl proc used to handle errors encountered during
drag&drop operations. If a proc is not specified, this command
returns the current error handler. By default, all errors are
sent to the usual tkerror command, and therefore appear in a
dialog box to the user. This behavior is quite useful when
debugging communication protocols, but may not be desirable in a
finished application. Errors can be suppressed entirely (leav‐
ing the rejection symbol as the only error indicator) by speci‐
fying a null string in place of the proc name.
drag&drop location ?x y?
Used to set or query the pointer location during a drag&drop
operation. The x y arguments specify the current location; if
these arguments are missing, then the last reported (x,y) loca‐
tion is returned as a list with two elements. This command is
issued automatically within the drag&drop drag and drag&drop
drop commands, to keep track of pointer movement.
KEYWORDS
drag&drop, send, bind, widget
BLT 2.4 drag&drop(n)
