Ubuntu Manpage: drag&drop - facilities for handling drag&drop data transfers

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 managing drag-and-drop
data transfers. Any of the usual Tk widgets can be registered to participate in the drag-
and-drop process. Widgets registered 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 message 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 interact 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 communication 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 registered.

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 operation. 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 symbol (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 operations. 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 potential 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 incompatible, and is ignored. By
default, this option has the value "all", indicating that all dataTypes
should be considered 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 automatically 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, center, nw, ne, sw or se. For example, "nw" means to position
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 communication 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 registered.

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" command. 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 substituted 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 registered for the target
window, and invokes the appropriate command. 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 target.

drag&drop token window
Returns the token window associated with a drag&drop source window. 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 handler 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
<ButtonRelease-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 (leaving the rejection symbol as the only error
indicator) by specifying 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) location 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