Short explanation of how qPref works
System startup:
core/qt-init.cpp init_qt_late()
does
qPref::load();
to load all properties from all qPref* classes
System shutdown:
subsurface-mobile-main.cpp and subsurface-desktop-main.cpp main()
calls
call qPref::sync()
to save all changes to disk, this is needed because part of the program modifies struct preferences instead of calling the set method.
EXCEPTION:
Variables not present in struct preferences (local static variables in the class are not written, see later.
System startup/shutdown common handling:
qPref::load() calls qPref::doSync(false)
qPref::sync() calls qPref::doSync(true)
qPrefDoSync()
qPref::doSync() calls qPref::doSync() for all qPref* classes Meaning qPref knows which classes exist, but not which variables
qPref*::doSync() calls
disk_<variable name>() for each variable
EXCEPTION:
some variables are not in struct preferences, but local static variables which can only be accessed through the set/get functions, therefore there are no need to sync them
if (!doSync) // meaining load
load_<variable_name>()
qPref*::disk_*()
qPref*::disk_*() calls qPrefPrivate::propSetValue to save a property, and qPrefPrivate::propValue() to read a property. The function also keeps struct preferences in sync.
qPrefPrivate::propSetValue()
qPrefPrivate::propSetValue() is static and calls QSettings to write property
qPrefPrivate::propValue()
qPrefPrivate::propValue() is static and calls QSettings to read property
macros
the macros are defined in qPrefPrivate.h
the macros are used in qPref*cpp
Reading properties
Reading a property is done through an inline function, and thus no more expensive than accessing the variable directly.
qPref*::<variable_name>()
Setting properties
Setting a property is done through a dedicated set function which are static to simplify the call:
qPref<class>::set_<variable_name>(value)
like:
qPrefDisplay::animation_speed(500);
the set function updates struct preferences (if not a local variable), and saves the property to disk, however save is only done if the variable is changed.
Updating struct preferences
When a program part updates struct preferences directly, changes are NOT saved to disk if the programm crashes, otherwise all variables are saved to disk with the program exists.