Data persistence and app updates

hi,

i'm developing app requires property list first time, , i'm little confused file system , conventions of using it. especially, when future app versions developed , plist needs updating.

when app opens, plist should installed persists lifetime of app version (i.e. until updated or uninstalled). i'd know tips , tricks experienced developers may have dealing situations this.

suppose logical development strategy goes this:

when writing sandbox directory
// search directory , find path (append name of file, extension, on path)
// if not found, create
// log error

found code online mentioned taking app versions consideration, makes lot of sense if intend update app in future. not of steps clear me , i'm hoping can me understand steps i'm unclear with.

// search directory , instantiate nsuserdefaults ready key/value retrieve of app version in next step

code:

nsfilemanager *deffm = [nsfilemanager defaultmanager];  	nsstring *docsdir = [nssearchpathfordirectoriesindomains(nsdocumentdirectory,nsuserdomainmask, yes) objectatindex:0];  	nsuserdefaults *userdefaults = [nsuserdefaults standarduserdefaults];

// statically declare current app version , retrieve older app version nsuserdefaults, compare. if appropriate, execute block.
// block sets app version, assigning new key/value in nsuserdefaults.
// block continues to: find appdirectory , docdirectory? find confusing. should data saved?

code:

//..stuff done once when installing new version....  	static nsstring *appversionkey = @"myappversion";  	int lastversion = [userdefaults integerforkey: appversionkey];  	if( lastversion != thisversion )	//..do once after install..  	{  		[userdefaults setinteger: thisversion forkey: appversionkey];  		nsstring *appdir = [[nsbundle mainbundle] resourcepath];  		nsstring *src = [appdir stringbyappendingpathcomponent: @"xcodemade.plist"];  		nsstring *dest = [docsdir stringbyappendingpathcomponent: @"xcodemade.plist"];  		[deffm removeitematpath: dest error: null];  //..remove old copy  		[deffm copyitematpath: src topath: dest error: null];  	}  //..end of stuff done once when installing new version.

would write code differently, or cover pretty well?

 

nashyo said: ↑

would write code differently, or cover pretty well?

click expand...

yes, write differently. not think in "files containing preferences". think in terms of values , keys make preference. let nsuserpreferences persisting. not overwrite existing settings user has chosen.

migration strategy should add new keys nsuserdefaults dictionary. check version stored in nsuserpreferences: if version indicates setting known access key. if version indicates setting unknown add setting using defaults.

ever do, keep users settings. user tend upset if app deletes settings during update.

- olaf

 

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