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<A HREF="#toc">Table of Contents</A><P>
<H2><A NAME="sect0" HREF="#toc0">Name</A></H2>
drag&drop - facilities for handling drag&drop data
transfers
<H2><A NAME="sect1" HREF="#toc1">Synopsis</A></H2>
<B>drag&drop source </B><BR>
<B>drag&drop source <I>window </I></B>?<I>options</I>? <BR>
<B>drag&drop source <I>window <B>handler </B></I></B>?<I>dataType</I>? ?<I>command arg arg...</I>? <P>
<B>drag&drop target
</B><BR>
<B>drag&drop target <I>window <B>handler </B></I></B>?<I>dataType command arg arg...</I>? <P>
<B>drag&drop target
<I>window <B>handle <I>dataType</I></B></I></B> ?<I>value</I>? <P>
<B>drag&drop token <I>window </I></B><P>
<B>drag&drop drag <I>window
x y </I></B><BR>
<B>drag&drop drop <I>window x y </I></B><BR>
<B>drag&drop active </B><BR>
<B>drag&drop errors </B>?<I>proc</I>? <BR>
<B>drag&drop location </B>?<I>x y</I>? <P>
<H2><A NAME="sect2" HREF="#toc2">Description</A></H2>
<P>
The <B>drag&drop</B> 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 <I>source</I> can export data to other
widgets registered as a drag&drop <I>target</I>. Note that a particular widget
can be registered as a source, as a target, or as both. <P>
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.
<P>
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. <P>
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"). <P>
This introduction was presented as a brief
overview of the communication process; further details are presented below:
<DL>
<DT><B>drag&drop source</B> </DT>
<DD>Returns a list of path names for widgets registered as
drag&drop sources. Returns an empty string if no widgets have been registered.
</DD>
<DT><B>drag&drop source <I>window </I></B>?<I>options</I>? </DT>
<DD>Registers a new drag&drop source window
with the given options, or modifies the options for an existing window:
<blockquote></DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>buttonBinding</B>
Class:<tt> </tt> <tt> </tt> <B>ButtonBinding</B>
Switch:<tt> </tt> <tt> </tt> <B>-button</B> <I>n</I>
</PRE>
<DL>
<DT>Specifies the mouse button (integer 1-5) that will invoke the drag&drop </DT>
<DD>operation
on the source window. This causes the following bindings to be added to
the widget: <P>
<BR>
<PRE><I>bind <I>win</I></I> <ButtonPress-<I>n</I>> {drag&drop drag %W %X %Y}
<I>bind <I>win</I></I> <B<I>n</I>-Motion> {drag&drop drag %W %X %Y}
<I>bind <I>win</I></I> <ButtonRelease-<I>n</I>> {drag&drop drop %W %X %Y}
</PRE><P>
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. <P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>packageCommand</B>
Class:<tt> </tt> <tt> </tt> <B>Command</B>
Switch:<tt> </tt> <tt> </tt> <B>-packagecmd <I>command</I></B>
</PRE>
<DL>
<DT>Specifies a Tcl command used to establish the appearance of the token </DT>
<DD>window
at the start of each drag&drop operation. This command is automatically
invoked by the <B>drag&drop drag</B> 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. </DD>
</DL>
<P>
The following substitutions
are made in the <I>command</I> string before it is executed: <blockquote>
<DL>
<DT><B>%t</B> </DT>
<DD>Replaced with
the window path name for the token which represents the data being dragged.
</DD>
<DT><B>%W</B> </DT>
<DD>Replaced with the window path name for the drag&drop source. </DD>
</DL>
</blockquote>
<P>
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. <P>
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 <B>drag&drop location</B>
command to determine the entry in the listbox that the user has selected
and it returns this as the data value: <P>
<BR>
<PRE><I>proc package_list_item {lbox token} {</I>
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
}
</PRE><P>
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. <P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>rejectBackground</B>
Class:<tt> </tt> <tt> </tt> <B>Background</B>
Switch:<tt> </tt> <tt> </tt> <B>-rejectbg <I>color</I></B>
</PRE>
<DL>
<DT>Specifies the color used to draw the background of the rejection symbol
</DT>
<DD>on the token window. The rejection symbol (a circle with a line through
it--the international "no") appears whenever communication fails. </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>rejectForeground</B>
Class:<tt> </tt> <tt> </tt> <B>Foreground</B>
Switch:<tt> </tt> <tt> </tt> <B>-rejectfg <I>color</I></B>
</PRE>
<DL>
<DT>Specifies the color used to draw the foreground of the rejection symbol
</DT>
<DD>on the token window. </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>rejectStipple</B>
Class:<tt> </tt> <tt> </tt> <B>Stipple</B>
Switch:<tt> </tt> <tt> </tt> <B>-rejectstipple <I>pattern</I></B>
</PRE>
<DL>
<DT>Specifies a stipple pattern used to draw the foreground of the rejection
</DT>
<DD>symbol on the token window. Any of the forms acceptable to Tk_GetBitmap
can be used. </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>selfTarget</B>
Class:<tt> </tt> <tt> </tt> <B>SelfTarget</B>
Switch:<tt> </tt> <tt> </tt> <B>-selftarget <I>boolean</I></B>
</PRE>
<DL>
<DT>If the <I>boolean</I> value is true, and if a source widget is also </DT>
<DD>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. </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>send</B>
Class:<tt> </tt> <tt> </tt> <B>Send</B>
Switch:<tt> </tt> <tt> </tt> <B>-send <I>list</I></B>
</PRE>
<DL>
<DT>Specifies a <I>list</I> of <I>dataTypes</I> enabled for communication. Only </DT>
<DD><I>dataTypes</I>
defined by commands of the form "<B>drag&drop source <I>window <B>handler </B></I></B>?<I>dataType</I>
?<I>command arg arg...</I>?" are allowed. This list also determines the priority
of the various <I>dataTypes</I>. When a token window is over a potential drag&drop
target, this list is searched from start to finish for a <I>dataType</I> that
is also recognized by the target. The first matching <I>dataType</I> found determines
the value that will be sent if the token is dropped. If no matching <I>dataType</I>
is found, then the target is incompatible, and is ignored. By default,
this option has the value "all", indicating that all <I>dataTypes</I> should be
considered in the order that they were defined for the source. </DD>
</DL>
<P>
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. <P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>siteCommand</B>
Class:<tt> </tt> <tt> </tt> <B>Command</B>
Switch:<tt> </tt> <tt> </tt> <B>-sitecmd <I>command</I></B>
</PRE>
<DL>
<DT>Specifies a Tcl command used to update the appearance of the token window.
</DT>
<DD>If specified, this command is automatically invoked by the <B>drag&drop drag</B>
command whenever the token window is over a compatible drag&drop target.
</DD>
</DL>
<P>
The following substitutions are made in the <I>command</I> string before it is
executed: <blockquote>
<DL>
<DT><B>%s</B> </DT>
<DD>Replaced with "1" if the token window is over a compatible
target, and "0" otherwise. </DD>
<DT><B>%t</B> </DT>
<DD>Replaced with the window path name for the
token which represents the data being dragged. </DD>
</DL>
</blockquote>
<P>
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. <P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>tokenAnchor</B>
Class:<tt> </tt> <tt> </tt> <B>Anchor</B>
Switch:<tt> </tt> <tt> </tt> <B>-tokenanchor <I>anchor</I></B>
</PRE>
<DL>
<DT>Specifies how the token window is positioned relative to the mouse </DT>
<DD>pointer
coordinates passed to the <B>drag&drop drag</B> 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". </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>tokenBackground</B>
Class:<tt> </tt> <tt> </tt> <B>Background</B>
Switch:<tt> </tt> <tt> </tt> <B>-tokenbg <I>color</I></B>
</PRE>
<DL>
<DT>Specifies the color used to draw the background of the token window. </DT>
<DD></DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>tokenBorderWidth</B>
Class:<tt> </tt> <tt> </tt> <B>BorderWidth</B>
Switch:<tt> </tt> <tt> </tt> <B>-tokenborderwidth <I>size</I></B>
</PRE>
<DL>
<DT>Specifies the width in pixels of the border around the token window. </DT>
<DD>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". </DD>
</DL>
<P>
<BR>
<PRE>Name:<tt> </tt> <tt> </tt> <B>tokenCursor</B>
Class:<tt> </tt> <tt> </tt> <B>Cursor</B>
Switch:<tt> </tt> <tt> </tt> <B>-tokencursor <I>cursor</I></B>
</PRE>
<DL>
<DT>Specifies the cursor used when a token window is active. The value </DT>
<DD>may
have any of the forms acceptable to Tk_GetCursor. The default value is
"center_ptr". </DD>
</DL>
</blockquote>
<DL>
<DT><B>drag&drop source <I>window <B>handler </B></I></B>?<I>dataType</I>? ?<I>command arg arg...</I>?
</DT>
<DD>With no extra arguments, this command returns a list of all <I>dataType</I> names
that have been registered for the source <I>window</I>. If only the <I>dataType</I> is
specified, then the <I>dataType</I> is created if necessary, and the command associated
with the <I>dataType</I> is returned. Otherwise, it concatenates the <I>command</I> and
any extra <I>arg</I> strings, and registers a new <I>dataType</I> with this command. </DD>
</DL>
<P>
The
following substitutions are made in the <I>command</I> string before it is executed:
<blockquote>
<DL>
<DT><B>%i</B> </DT>
<DD>Replaced with the name of the interpreter for the target application.
</DD>
<DT><B>%v</B> </DT>
<DD>Replaced with the value returned from the "-packagecmd" command. </DD>
<DT><B>%w</B> </DT>
<DD>Replaced
with the window path name for the target window. </DD>
</DL>
</blockquote>
<P>
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 <I>command</I> handler is automatically substituted
into the "%v" fields of the target handler. <P>
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. </blockquote>
<P>
<DL>
<DT><B>drag&drop target</B> </DT>
<DD>Returns
a list of path names for widgets registered as drag&drop targets. Returns
an empty string if no widgets have been registered. </DD>
<DT><B>drag&drop target <I>window
<B>handler </B></I></B>?<I>dataType command arg arg...</I>? </DT>
<DD>Registers a new drag&drop target window
with a given handler, or modifies the handlers for an existing window.
If no <I>dataType</I> is specified, this command returns the current list of recognized
<I>dataType</I> strings. Each <I>dataType</I> is a symbolic name representing a form
of data, and the corresponding <I>command</I> 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. </DD>
</DL>
<P>
The following
substitutions are made in the <I>command</I> string before it is executed: <blockquote>
<DL>
<DT><B>%v</B>
</DT>
<DD>In the simplest case, the source window does not have a handler command
for the selected <I>dataType</I>, 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. </DD>
<DT><B>%W</B> </DT>
<DD>Replaced with the window path name for the target window.
</DD>
</DL>
</blockquote>
<DL>
<DT><B>drag&drop target <I>window </I></B>handle <I>dataType</I> ?<I>value</I>? </DT>
<DD>Searches for the given <I>dataType</I>
name among the handlers registered for the target <I>window</I>, and invokes the
appropriate <I>command</I>. If a <I>value</I> is specified, it is substituted into any
"%v" fields in the handler command associated with the <I>dataType</I>. If the
<I>dataType</I> 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. </DD>
<DT><B>drag&drop token <I>window</I></B> </DT>
<DD>Returns the token window
associated with a drag&drop source <I>window</I>. 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, <P>
<BR>
<PRE><I>drag&drop source .foo</I>
set win [drag&drop token .foo]
label $win.label -text "Data"
pack $win.label
</PRE><P>
<DL>
<DT><B>drag&drop drag <I>window x y</I></B> </DT>
<DD>Marks the start of (or movement during) a drag&drop
operation. If the token window is unmapped when this command is invoked,
then the <B>-packagecmd</B> for the source <I>window</I> 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 <I>x y</I> location.
Unless the "<B>-button 0</B>" option is specified for the source, this command
is automatically bound to <ButtonPress-<I>n</I>> and <B<I>n</I>-Motion> events for "<B>-button
<I>n</I></B>" of the source widget. </DD>
<DT><B>drag&drop drop <I>window x y</I></B> </DT>
<DD>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 <I>dataType</I> 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
"<B>-button 0</B>" option is specified for the source, this command is automatically
bound to the <ButtonRelease-<I>n</I>> event for "<B>-button <I>n</I></B>" of the source widget. </DD>
<DT><B>drag&drop
active</B> </DT>
<DD>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). </DD>
<DT><B>drag&drop errors </B>?<I>proc</I>? </DT>
<DD>Specifies a Tcl <I>proc</I>
used to handle errors encountered during drag&drop operations. If a <I>proc</I>
is not specified, this command returns the current error handler. By default,
all errors are sent to the usual <B>tkerror</B> 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 <I>proc</I>
name. </DD>
<DT><B>drag&drop location </B>?<I>x y</I>? </DT>
<DD>Used to set or query the pointer location
during a drag&drop operation. The <I>x y</I> 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 <B>drag&drop drag</B> and <B>drag&drop drop</B> commands, to keep track of pointer
movement. <P>
</DD>
</DL>
<H2><A NAME="sect3" HREF="#toc3">Keywords</A></H2>
drag&drop, send, bind, widget <P>
<HR><P>
<A NAME="toc"><B>Table of Contents</B></A><P>
<UL>
<LI><A NAME="toc0" HREF="#sect0">Name</A></LI>
<LI><A NAME="toc1" HREF="#sect1">Synopsis</A></LI>
<LI><A NAME="toc2" HREF="#sect2">Description</A></LI>
<LI><A NAME="toc3" HREF="#sect3">Keywords</A></LI>
</UL>
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