[Chapter 18] 18.10 The Listbox Widget

18.10 The Listbox Widget

Create a listbox with the Listbox method. You can then insert items into the listbox using the insert method.

$parentwidget->Listbox (options)

The standard configuration options that apply to Listbox are: -background, -bg, -borderwidth, -bd, -cursor, -exportselection, -font, -foreground, -fg, -height, -highlightbackground, -highlightcolor, -highlightthickness, -relief, -selectbackground, -selectborderwidth, -selectforeground, -takefocus, -width, -xscrollcommand, and -yscrollcommand.

Other options are:

-selectmode => mode

Determines how many items can be selected at once, as well as key/mouse bindings. mode can be any of:

'single': Only one item can be selected at a time.
'browse': Only one item can be selected at a time. (Default).
'multiple': Multiple items can be selected at a time.
'extended': Multiple items can be selected at a time.

-setgrid => boolean

Turns on gridding for the listbox. If the widget is resized, only complete lines and characters are displayed. Default is 0 (off).

18.10.1 Listbox Indexes

In a Listbox widget, several indexes are defined to identify positions in the listbox, for use by the methods used for retrieving or manipulating listbox entries. These indexes are:

n: An integer representing a position in the list, with 0 as the first item.
active: The item with the keyboard focus.
anchor: The anchored position.
end: The last element in the listbox.
@x,y: The listbox item containing the specified x,y coordinate.

18.10.2 Listbox Methods

In addition to configure and cget, the following methods are supported by Listbox:

insert

Adds items to a listbox at the specified index. For example, to insert items at the end of a list:

$listbox->insert('end', "Puerto Rico", "Virgin Islands", "Guam");

delete

Deletes items from a listbox. To delete all items:

$listbox->delete(0,'end');

get

Returns a list of elements within the specified range of indexes. For a list of all elements:

@items = $listbox->get(0,'end');

curselection

Returns a list of all currently selected elements in the listbox.

activate

Sets the specified item to be the active element.

bbox

Returns the location and dimensions of the bounding box surrounding the specified listbox element. The returned list contains four numbers representing (respectively) the x coordinate of the upper-left corner, the y coordinate of the upper-left corner, the width of the text in pixels, and the height of the text in pixels.

index

Converts a named index into a numeric one.

nearest

Gets the index of the listbox item nearest to a given y coordinate.

see

Pages the listbox up or down to display the specified item.

selection

Manipulates the selected block of list items. The first argument can be any of:

anchor

Sets the anchor index to the specified index.

clear

Clears any selected list items in the specified range. For example, to clear all selections:

$listbox->selection('clear', 0, 'end');

includes

Returns 0 or 1 depending on whether the specified item is already selected.

$listbox->selection('includes', 'end');

set

Selects a range of items in the listbox.

$listbox->selection('set', 0, 'end');

size

Returns the total number of items in the listbox.

xview

Manipulates the text in view. With no arguments, returns a list of two numbers between 0 and 1, defining what portion of the list text is currently hidden on the left and right sides, respectively. With arguments, the function of xview changes:

index: If the first argument is an index, that position becomes the leftmost position in view.
moveto: Moves the specified fraction of the listbox to the left of the visible portion.
scroll: Scrolls the text left or right by the specified number of units (characters, in this context) or pages. Used primarily as a callback to a scrollbar; pressing on an arrow would move by units (characters), and pressing on the trough would move by pages. The number is either 1 or -1, to move forwards or backwards, respectively.

yview

Manipulates the text in view. With no arguments, returns a list of two numbers between 0 and 1, defining what portion of the list text is currently hidden on the top and bottom, respectively. With arguments, the function of yview changes:

index: If the first argument is an index, that position becomes the topmost position in view.
moveto: Moves the specified fraction of the listbox to the top of the visible portion.
scroll: Scrolls the text up or down by the specified number of units (lines, in this context) or pages. Used primarily as a callback to a scrollbar; pressing on an arrow would move by units (lines), and pressing on the trough would move by pages. The number is either 1 or -1, to move forwards or backwards, respectively.


18.9 The Scrollbar Widget		18.11 The Text Widget