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## pixmap-column-mixin

A non-instantiable class that can be mixed with the `grid-column` class to create grid columns whose cells draw pixmaps that represent user values. Each cell in the column will display a pixmap if the row of that cell is an instance of a `grid-row` subclass that mixes in the `widget-row-mixin` class.

To ensure that this mixin class' methods take precedence over other methods that specialize on `grid-column`, this mixin class generally should appear first in a defclass expression's list of superclasses, as in:

    (defclass my-pixmap-column
      (pixmap-column-mixin my-subclass-of-grid-column) ...)

The draw-cell method provided by this mixin will draw (in each cell of the grid column) a pixmap that is associated with an application value, if a pixmap has been supplied for that value. First read-cell-value is called as usual to find the application value to display (this typically calls the column's data-reader function). Then the pixmap-alist of the `grid-column` is searched to find an entry whose first element is that user value. If a match is found, then the second element of the alist entry is taken to be the name of a pixmap. If find-pixmap finds a cached pixmap by that name, then it is displayed in the cell. Otherwise the cell will be drawn blank.

If the stretching property of the `grid-column` is true, then the pixmap will be expanded or shrunk as needed to exactly fit the cell. Otherwise the pixmap will be drawn at its natural size.

If the user-modifiable property of the `grid-column` is true, then the user may cycle through the set of pixmaps by clicking the grid cell or pressing the spacebar when it has the keyboard focus. Each time a new pixmap is displayed, write-cell-value is called to write the associated data-value back into the data-object of the grid-row (this typically calls the column's data-writer function).

Here is a typical expression for creating a pixmap grid column. It assumes that the data-object of each `grid-row` has a slot accessor called access containing one of the values `:none`, `:partial`, or `:full`.

    (make-instance 'my-pixmap-column
      :name :access
      :proportional nil
      :section-size 24
      :data-reader 'access
      :data-writer '(setf access)
      :pixmap-alist '((:none nil)
                      (:partial :key)
                      (:full :key-special))

The Employee grid example in the Navigator Dialog includes a pixmap column that displays pictures of keys as in the code snippet above.

See the section Built-In Grid Cell Widgets on the page for the `grid-widget` class for an overview of the grid column mixins.

A quicker but less object-oriented alternative to using the `widget-column-mixin` classes is to write cell-widget methods.

Copyright (c) 1998-2022, Franz Inc. Lafayette, CA., USA. All rights reserved.
This page was not revised from the 10.0 page.
Created 2019.8.20.

|  | ToC | DocOverview | CGDoc | RelNotes | FAQ | Index | PermutedIndex
| Allegro CL version 10.1 Unrevised from 10.0 to 10.1. 10.0 version