About Callback Reasons (DCL)

The callback reason, returned in the $reason variable, specifies why the action occurred.

Note: DCL support in AutoLISP is limited to Windows only.

The variable’s value is set for any kind of action, but you need to inspect it only when the action is associated with an edit_box, list_box, image_button, or slider tile. The following outlines the values of each callback reason code:

Code 1

This is the value for most action tiles. The user has selected the tile (possibly by pressing Enter, if the tile is the default and the platform recognizes accelerator keys).

Code 2 – Edit Boxes

The user has exited the edit box—by pressing the Tab key or by choosing a different tile—but has not made a final selection. If this is the reason for an edit box callback, your application should not update the value of the associated variable, but should check the validity of the value in the edit box.

Code 3 – Sliders

The user has changed the value of the slider by dragging the indicator (or an equivalent action), but has not made a final selection. If this is the reason for a slider callback, your application should not update the value of the associated variable but should update the text that displays the slider's status.

Code 4 – List Boxes and Image Buttons

This callback reason always follows a code 1. It usually means “commit to the previous selection.” It should never undo the previous selection; this confuses and annoys the user.

• List boxes: The user has double-clicked on the list box. You can define the meaning of a double-click in your application. If the main purpose of the dialog box is to select a list item, a double-click should make a selection and then exit the dialog box. (In this case, the is_default attribute of the list_box tile should be true.) If the list box is not the primary tile in the dialog box, then a double-click should be treated as equivalent to making a selection (code 1).

  List boxes that allow the user to select multiple items (multiple_select = true) cannot support double-clicking.

• Image buttons: The user has double-clicked on the image button. You can define the meaning of a double-click in your application. In many cases it is appropriate for a single-click to select the button, but in others it is better for a single-click (or a keyboard action) to highlight the button, and then have the Enter key or a double-click select it.