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.

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This page was not revised from the 10.0 page.
Created 2019.8.20.