Callback Substitution

Callback Substitution

When Motif executes a callback in reaction to some event, it provides some parameters (such as the current widget) or additional data relevant to a given class. Tm follows Tk in providing the powerful mechanism of callback substitution. Before execution, the Tcl command list is scanned to look for the % character. Each time this character is found, the word that follows is extracted, analyzed, and if recognized, replaced with the corresponding data.

For example, %item in an xmList callback is replaced by the item selected, whereas %item_position is replaced by its position in the list. This is an example of callback substitution in a list:

.list singleSelectionCallback
    { print_info %item %item_position }
proc print_info item position
    { puts stdout "item was $item, at position $position" }

The following list shows the recognized tags. Their meaning is detailed below in the context of the corresponding callbacks.

%click_count %endPos %newinsert %selection_type
%closure %item_length %pattern_Length %set
%currInsert %item_position %pattern_length %startPos
%currinsert %item %Pattern %type
%dir_length %length %pattern %value_length
%dir %mask_length %ptr %value
%doit %mask %reason %w
%dragContext %newInsert %selected_items

The following list contains the possible callback reasons, as defined in <Xm/Xm.h> (but with the leading XmCR_ removed):

activate apply arm
browse_select cancel cascading
clipboard_data_delete clipboard_data_request command_changed
command_entered create decrement
default_action disarm drag
execute expose extended_select
focus gain_primary help
increment input lose_primary
losing_focus map modifying_text_value
moving_insert_cursor multiple_select no_match
none obscured_traversal ok
page_decrement page_increment protocols
resize single_select tear_off_activate
tear_off_deactivate to_bottom to_top
unmap value_changed

%click_count	%endPos	%newinsert	%selection_type
%closure	%item_length	%pattern_Length	%set
%currInsert	%item_position	%pattern_length	%startPos
%currinsert	%item	%Pattern	%type
%dir_length	%length	%pattern	%value_length
%dir	%mask_length	%ptr	%value
%doit	%mask	%reason	%w
%dragContext	%newInsert	%selected_items

activate	apply	arm
browse_select	cancel	cascading
clipboard_data_delete	clipboard_data_request	command_changed
command_entered	create	decrement
default_action	disarm	drag
execute	expose	extended_select
focus	gain_primary	help
increment	input	lose_primary
losing_focus	map	modifying_text_value
moving_insert_cursor	multiple_select	no_match
none	obscured_traversal	ok
page_decrement	page_increment	protocols
resize	single_select	tear_off_activate
tear_off_deactivate	to_bottom	to_top
unmap	value_changed