# List Widget

    Application header file	<X11/Xaw/List.h>

    Class header file	<X11/Xaw/ListP.h>

    Class	listWidgetClass

    Class Name	List

    Superclass	Simple

The List widget contains a list of strings formatted into rows and columns. When one of the strings is selected, it is highlighted, and the List widget's `Notify` action is invoked, calling all routines on its callback list. Only one string may be selected at a time.

## Resources

When creating a List widget instance, the following resources are retrieved from the argument list or from the resource database:

Name | Class | Type | Notes | Default Value
--- | --- | --- | --- | ---
accelerators | Accelerators | AcceleratorTable |  | NULL
ancestorSensitive | AncestorSensitive | Boolean | D | True
background | Background | Pixel |  | XtDefaultBackground
backgroundPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderColor | BorderColor | Pixel |  | XtDefaultForeground
borderPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderWidth | BorderWidth | Dimension |  | 1
callback | Callback | Callback |  | NULL
colormap | Colormap | Colormap |  | Parent's Colormap
columnSpacing | Spacing | Dimension |  | 6
cursor | Cursor | Cursor |  | XC_left_ptr
cursorName | Cursor | String |  | NULL
defaultColumns | Columns | int |  | 2
depth | Depth | int | C | Parent's Depth
destroyCallback | Callback | XtCallbackList |  | NULL
font | Font | FontStruct |  | XtDefaultFont
fontSet | FontSet | XFontSet |  | XtDefaultFontSet
forceColumns | Columns | Boolean |  | False
foreground | Foreground | Pixel |  | XtDefaultForeground
height | Height | Dimension | A | Enough space to contain the list
insensitiveBorder | Insensitive | Pixmap |  | GreyPixmap
internalHeight | Height | Dimension |  | 2
internalWidth | Width | Dimension |  | 4
international | International | Boolean | C | False
list | List | Pointer |  | name of widget
longest | Longest | int | A | 0
mappedWhenManaged | MappedWhenManaged | Boolean |  | True
numberStrings | NumberStrings | int | A | computed for NULL terminated list
pasteBuffer | Boolean | Boolean |  | False
pointerColor | Foreground | Pixel |  | XtDefaultForeground
pointerColorBackground | Background | Pixel |  | XtDefaultBackground
rowSpacing | Spacing | Dimension |  | 2
screen | Screen | Screen | R | Parent's Screen
sensitive | Sensitive | Boolean |  | True
translations | Translations | TranslationTable |  | See below
verticalList | Boolean | Boolean |  | False
width | Width | Dimension | A | Enough space to contain the list
x | Position | Position |  | 0
y | Position | Position |  | 0
_

`callback`

  All functions on this list are called whenever the `notify` action is invoked. The call_data argument contains information about the element selected and is described in detail in the `List Callbacks` section.

`columnSpacing`

`rowSpacing`

  The amount of space, in pixels, between each of the rows and columns in the list.

`defaultColumns`

  The default number of columns. This value is used when neither the width nor the height of the List widget is specified or when `forceColumns` is `True`.

`font`

  The text font to use when displaying the `list`, when the `international` resource is `false`.

`fontSet`

  The text font set to use when displaying the `list`, when the `international` resource is `true`.

`forceColumns`

  Forces the default number of columns to be used regardless of the List widget's current size.

`foreground`

  A pixel value which indexes the widget's colormap to derive the color used to paint the text of the list elements.

\fPinternalHeight\fP

\fPinternalWidth\fP

  The margin, in pixels, between the edges of the list and the corresponding edge of the List widget's window.

`list`

  An array of text strings displayed in the List widget. If `numberStrings` is zero (the default) then the `list` must be NULL terminated. If a value is not specified for the `list`, then `numberStrings` is set to 1, and the name of the widget is used as the `list`, and `longest` is set to the length of the name of the widget. The `list` is used in place, and must be available to the List widget for the lifetime of this widget, or until it is changed with `XtSetValues` or `XawListChange`.

`longest`

  Specifies the width, in pixels, of the longest string in the current list. The List widget will compute this value if zero (the default) is specified. If this resource is set by hand, entries longer than this will be clipped to fit.

`numberStrings`

  The number of strings in the current list. If a value of zero (the default) is specified, the List widget will compute it. When computing the number of strings the List widget assumes that the `list` is NULL terminated.

`pasteBuffer`

  If this resource is set to `True` then the name of the currently selected list element will be put into `CUT_BUFFER_0`.

`verticalList`

  If this resource is set to `True` then the list elements will be presented in column major order.

## List Actions

The List widget supports the following actions:

- Highlighting and unhighlighting the list element under the pointer with `Set` and `Unset`

- Processing application callbacks with `Notify`

The following is the default translation table used by the List Widget:

    <Btn1Down>,<Btn1Up>:	Set(\|) Notify(\|)

The full list of actions supported by List widget is:

`Set`(\|)

  Sets the list element that is currently under the pointer. To inform the user that this element is currently set, it is drawn with foreground and background colors reversed. If this action is called when there is no list element under the cursor, the currently set element will be unset.

`Unset`(\|)

  Cancels the set state of the element under the pointer, and redraws it with normal foreground and background colors.

`Notify`(\|)

  Calls all callbacks on the List widget's callback list. Information about the currently selected list element is passed in the call_data argument (see `List Callbacks` below).

## List Callbacks

All procedures on the List widget's callback list will have a `XawListReturnStruct` passed to them as call_data. The structure is defined in the List widget's application header file.

    typedef struct _XawListReturnStruct {
    	String string;	/* string shown in the list. */
    	int list_index;	/* index of the item selected. */
    } XawListReturnStruct;

The list_index item used to be called simply index. Unfortunately, this name collided with a global name defined on some operating systems, and had to be changed.

## Changing the List

To change the list that is displayed, use `XawListChange .`

      void XawListChange
      Widget w
      String* list
      intnitems, longest
      Boolean resize

w

  Specifies the List widget.

list

  Specifies the new list for the List widget to display.

nitems

  Specifies the number of items in the list. If a value less than 1 is specified, list must be NULL terminated, and the number of items will be calculated by the List widget.

longest

  Specifies the length of the longest item in the list in pixels. If a value less than 1 is specified, the List widget will calculate the value.

resize

  Specifies a Boolean value that if `True` indicates that the List widget should try to resize itself after making the change. The constraints of the List widget's parent are always enforced, regardless of the value specified here.

`XawListChange` will unset all list elements that are currently `set` before the list is actually changed. The list is used in place, and must remain usable for the lifetime of the List widget, or until list has been changed again with this function or with `XtSetValues`.

## Highlighting an Item

To highlight an item in the list, use `XawListHighlight .`

      void XawListHighlight
      Widget w
      int item

w

  Specifies the List widget.

item

  Specifies an index into the current list that indicates the item to be highlighted.

Only one item can be highlighted at a time. If an item is already highlighted when `XawListHighlight` is called, the highlighted item is unhighlighted before the new item is highlighted.

## Unhighlighting an Item

To unhighlight the currently highlighted item in the list, use `XawListUnhighlight .`

      void XawListUnhighlight
      Widget w

w

  Specifies the List widget.

## Retrieving the Currently Selected Item

To retrieve the list element that is currently set, use `XawListShowCurrent .`

      XawListReturnStruct *XawListShowCurrent
      Widget w

w

  Specifies the List widget.

`XawListShowCurrent` returns a pointer to an `XawListReturnStruct` structure, containing the currently highlighted item. If the value of the index member is XAW_LIST_NONE, the string member is undefined, and no item is currently selected.

## Restrictions

Many programmers create a ``scrolled list'' by putting a List widget with many entries as a child of a Viewport widget. The List continues to create a window as big as its contents, but that big window is only visible where it intersects the parent Viewport's window. (I.e., it is ``clipped.'')

While this is a useful technique, there is a serious drawback. X does not support windows above 32,767 pixels in width or height, but this height limit will be exceeded by a List's window when the List has many entries (i.e., with a 12 point font, about 3000 entries would be too many.)