### 2.2 listbox

listbox \- Create and manipulate listbox widgets

#### Synopsis

listbox pathName ?options?

#### Standard Options

    background       foreground  selectBackground   xScrollCommand
    borderWidth      font        selectBorderWidth  yScrollCommand
    cursor           geometry    selectForeground
    exportSelection  relief      setGrid

See options, for more information.

#### Arguments for Listbox

None.

#### Description

The listbox command creates a new window (given by the pathName argument) and makes it into a listbox widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the listbox such as its colors, font, text, and relief. The listbox command returns its pathName argument. At the time this command is invoked, there must not exist a window named pathName, but pathName’s parent must exist.

A listbox is a widget that displays a list of strings, one per line. When first created, a new listbox has no elements in its list. Elements may be added or deleted using widget commands described below. In addition, one or more elements may be selected as described below. If a listbox is exporting its selection (see exportSelection option), then it will observe the standard X11 protocols for handling the selection; listbox selections are available as type STRING, consisting of a Tcl list with one entry for each selected element.

For large lists only a subset of the list elements will be displayed in the listbox window at once; commands described below may be used to change the view in the window. Listboxes allow scrolling in both directions using the standard xScrollCommand and yScrollCommand options. They also support scanning, as described below.

#### A Listbox’s Arguments

The listbox command creates a new Tcl command whose name is pathName. This command may be used to invoke various operations on the widget. It has the following general form:

    pathName option ?arg arg ...?

Option and the args determine the exact behavior of the command. The following commands are possible for listbox widgets:

pathName :configure ?option? ?value option value ...?

  Query or modify the configuration options of the widget. If no option is specified, returns a list describing all of the available options for pathName (see Tk_ConfigureInfo for information on the format of this list). If option is specified with no value, then the command returns a list describing the one named option (this list will be identical to the corresponding sublist of the value returned if no option is specified). If one or more option:value pairs are specified, then the command modifies the given widget option(s) to have the given value(s); in this case the command returns an empty string. Option may have any of the values accepted by the listbox command.

pathName :curselection

  Returns a list containing the indices of all of the elements in the listbox that are currently selected. If there are no elements selected in the listbox then an empty string is returned.

pathName :delete first ?last?

  Delete one or more elements of the listbox. First and last give the integer indices of the first and last elements in the range to be deleted. If last isn’t specified it defaults to first, i.e. a single element is deleted. An index of 0 corresponds to the first element in the listbox. Either first or last may be specified as end, in which case it refers to the last element of the listbox. This command returns an empty string

pathName :get index

  Return the contents of the listbox element indicated by index. Index must be a non-negative integer (0 corresponds to the first element in the listbox), or it may also be specified as end to indicate the last element in the listbox.

pathName :insert index ?element element ...?

  Insert zero or more new elements in the list just before the element given by index. If index is specified as end then the new elements are added to the end of the list. Returns an empty string.

pathName :nearest y

  Given a y-coordinate within the listbox window, this command returns the index of the (visible) listbox element nearest to that y-coordinate.

pathName :scan option args

  This command is used to implement scanning on listboxes. It has two forms, depending on option:

  pathName :scan :mark x y

    Records x and y and the current view in the listbox window; used in conjunction with later scan dragto commands. Typically this command is associated with a mouse button press in the widget. It returns an empty string.

  pathName :scan :dragto x y.

    This command computes the difference between its x and y arguments and the x and y arguments to the last scan mark command for the widget. It then adjusts the view by 10 times the difference in coordinates. This command is typically associated with mouse motion events in the widget, to produce the effect of dragging the list at high speed through the window. The return value is an empty string.

pathName :select option arg

  This command is used to adjust the selection within a listbox. It has several forms, depending on option. In all of the forms the index end refers to the last element in the listbox.

  pathName :select :adjust index

    Locate the end of the selection nearest to the element given by index, and adjust that end of the selection to be at index (i.e including but not going beyond index). The other end of the selection is made the anchor point for future select to commands. If the selection isn’t currently in the listbox, then this command is identical to the select from widget command. Returns an empty string.

  pathName :select :clear

    If the selection is in this listbox then it is cleared so that none of the listbox’s elements are selected anymore.

  pathName :select :from index

    Set the selection to consist of element index, and make index the anchor point for future select to widget commands. Returns an empty string.

  pathName :select :to index

    Set the selection to consist of the elements from the anchor point to element index, inclusive. The anchor point is determined by the most recent select from or select adjust command in this widget. If the selection isn’t in this widget, this command is identical to select from. Returns an empty string.

pathName :size

  Returns a decimal string indicating the total number of elements in the listbox.

pathName :xview index

  Adjust the view in the listbox so that character position index is displayed at the left edge of the widget. Returns an empty string.

pathName :yview index

  Adjust the view in the listbox so that element index is displayed at the top of the widget. If index is specified as end it indicates the last element of the listbox. Returns an empty string.

#### "Default Bindings"

Tk automatically creates class bindings for listboxes that give them the following default behavior:

- [1] When button 1 is pressed over a listbox, the element underneath the mouse cursor is selected. The mouse can be dragged to select a range of elements.
- [2] The ends of the selection can be adjusted by dragging with mouse button 1 while the shift key is down; this will adjust the end of the selection that was nearest to the mouse cursor when button 1 was pressed.
- [3] The view in the listbox can be adjusted by dragging with mouse button 2.

The behavior of listboxes can be changed by defining new bindings for individual widgets or by redefining the class bindings. In addition, the procedure tk_listboxSingleSelect may be invoked to change listbox behavior so that only a single element may be selected at once.

#### Keywords

listbox, widget