html-widget-command-change

Arguments: widget command enabled?

Applicable on Windows only; not implemented on GTK.

This generic function is called whenever the state of an html-widget has changed such that one of the typical HTML-browsing commands should be enabled or disabled.

For example, if the user moves to the previous page and there is no further previous page after that, then this function will be called to tell you that the "Go Back" command should now be disabled. Your application could add a method to this generic function to disable whatever "Go Back" button it may have. The default method calls the html-widget's on-command-change function if it has one, so the application could instead attach an on-command-change function to an individual html-widget instance.

There is also a built-in method for the html-widget-for-browser subclass, which is used in html-browser dialogs, that modifies the html-browser's toolbar buttons as needed. So if you use an html-browser dialog, you should not need to write any html-widget-command-change methods (or supply any on-command-change functions), whereas if you use the lower-level html-widget control from scratch then you likely will.

html-widget is the html-widget whose state has changed.

command is one of the keyword symbols :back, :forward, or :cancel.

enabled? is true if the specified command should currently be enabled.

The :back and :forward commands refer to whether there are further pages in the linear chain of recently-visited pages, indicating whether any "Go Back" and "Go Forward" commands should currently be enabled.

The :cancel command refers to whether a page is currently being downloaded, indicating whether any "Cancel" command should be enabled. enabled? is passed as true when a download is beginning, and as nil when it has finished.

See the html-widget control.

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This page was not revised from the 9.0 page.
Created 2015.5.21.