Refactoring of preferences

[lucas-wilkins]

The following things need to be done to the preferences panel

• Cancel button -> 2316: Refactoring preferences #2358
• Preferences immediately saves the values, even if OK isn't clicked #2313 -> 2316: Refactoring preferences #2358
• Restore Defaults in the Preferences window does nothing #2312 -> 2316: Refactoring preferences #2358
• Changing preferences should prompt user to restart SasView #2317 -> 2317: Prompt user to restart when preferences change #2381

This can mostly be achieved through:

1. Modifying the preferences dialog system to have a more formal class structure
2. Better integration with config

[krzywon]

#2312: The PreferencesWidget class has a restoreDefaults attribute that houses a callable that is when the button is clicked. This just hasn't been implemented in any of the child classes yet. This should really change to a class method that child classes override. Update child classes to use this method. Question: should this reset the defaults in the current panel or in all panels?

#2313: Changes to make: Add a Cancel button, remove (most) connections from GUI elements, and update everything when the OK button is clicked. Would an Apply button be useful, too?

[pbeaucage]

#2313 another, potentially easier solution would be to change the underlying config class to have some method set like beginStagingChanges(), commitStagedChanges() and discardStagedChanges(). begin would be called on dialog open and basically copy() the structure to a backup place. Then commit...() would replace main copy with the edited copy and discard...() would replace the stored version with the editable copy.

[rozyczko]

Apply would still require app restart in general, wouldn't it? This means the behaviour would be identical to OK

[pbeaucage]

Not in general, depends on the config items. The Plotting ones all take effect immediately, as does the one added in Fitting in #2315

[lucas-wilkins]

Also, probably need to have a "your changes will not be applied untl you restart sasview" message for the display settings

[krzywon]

Comments from #2306 that I am documenting here:

• preferences.rst word-smithing - Added to PR 2316: GPU and Optimizer Options in Preferences Window #2399
• Potential performance improvements if one of bumps.fitting -or- bumps.options imports was removed from FittingPerspective.py (maybe needs it's own issue) - Out of scope
• Better handling of name passed when adding widgets - Added to PR 2316: Refactoring preferences #2358
• Add NotImplementedError to PreferencesWidget._addAllWidgets and planned PreferencesWidget.restoreDefaults - Added to PR 2316: Refactoring preferences #2358
• Better separation of GUI and logic for 'PreferencesWidget' children - Added to PR 2316: Refactoring preferences #2358
• Move fitting options window back into fitting perspective to retain the perspective-as-plugin framework - Added to PR 2316: GPU and Optimizer Options in Preferences Window #2399
• On display setting changes, create 'preview' window that displays button and widget scales - Ticketed in Preference Panel High DPI Setting Issues #2388

[krzywon]

Also, probably need to have a "your changes will not be applied untl you restart sasview" message for the display settings

See #2317 - Tracking what is changed, we could better handle when a restart is required and only prompt the user when necessary.