-- a question about how to make an object that is saved to the documents directory persist on the drive and be recoverable after the iDevice is rebooted.
Here's my problem. I make a data object with NSCoding and fill it with data. I write it to the documentsDirectory each time the data in the object are updated. I stop the app and start the app again, and my data object persists, with all of its data. But if I reboot the iPhone the code I wrote to recover and read the data object fails.
The code I wrote originally used only a NSString for the file path. It worked well under ios7 but it fails under ios8.
Reading up on things, I found this clue from the Apple documentation:
"Important: Although they are safe to use while your app is running, file reference URLs are not safe to store and reuse between launches of your app because a file’s ID may change if the system is rebooted. If you want to store the location of a file persistently between launches of your app, create a bookmark as described in Locating Files Using Bookmarks."
So I rewrote my ios7 file open and file close methods so they no longer use strings or urls but get their strings and urls from a bookmark that is saved using NSUserDefaults. Same problem: everything works fine so long as I do not power off the phone, but all is lost once I do. I am not able to solve this.
Here is my current series of steps. First I either determine (or if it already exists in NSUsrDefaults, I recover) the absolute path to the documentsDirectory, using a bookmark:
+ (NSString*) getGeoModelAbsolutePath
{
NSString *path;
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSURL *documentsDirectoryBookmarkURL;
NSData* documentsDirectoryBookmark = [userDefaults objectForKey:@"documentDirectoryBookmark"];
if(documentsDirectoryBookmark == nil)
{
documentsDirectoryBookmarkURL = [self getDocumentsDirectoryURL];
documentsDirectoryBookmark = [self bookmarkForURL:documentsDirectoryBookmarkURL];
}
documentsDirectoryBookmarkURL = [self urlForBookmark:documentsDirectoryBookmark];
path = documentsDirectoryBookmarkURL.path;
path = [path stringByAppendingString:@"/Model.mod"];
return path;
}
using methods modified from my ios7 code (which used only the getDocumentsDirectory method):
+ (NSString *)getDocumentsDirectory
{
NSURL *directory = [self getDocumentsDirectoryURL];
NSString * documentsDirectory = directory.path;
return documentsDirectory;
}
And
+ (NSURL *)getDocumentsDirectoryURL
{
NSURL *directory = [[[NSFileManager defaultManager]
URLsForDirectory:NSDocumentDirectory
inDomains:NSUserDomainMask]
lastObject];
return directory;
}
And
+ (NSData*)bookmarkForURL:(NSURL*)url {
NSError* theError = nil;
NSData* bookmark = [url bookmarkDataWithOptions:NSURLBookmarkCreationSuitableForBookmarkFile
includingResourceValuesForKeys:nil
relativeToURL:nil
error:&theError];
if (theError || (bookmark == nil)) {
// Handle any errors.
return nil;
}
return bookmark;
}
So now I have a NSString path with the model filename that I can use to get to the GeoModel
- (GeoModel*) openGeoModel
{
GeoModel *geoModel;
NSString* documentsDirectoryGeoModel =[FileManager getGeoModelAbsolutePath];
if([FileManager fileExistsAtAbsolutePath:documentsDirectoryGeoModel])
{
NSData* data = [NSData dataWithContentsOfFile: documentsDirectoryGeoModel]; //]documentsDirectoryGeoModel];
geoModel = [NSKeyedUnarchiver unarchiveObjectWithData: data];
NSString *unarchivedGeoModelVersion = geoModel.geoModel_VersionID;
if(![unarchivedGeoModelVersion isEqual: currentGeoModelVersion])
{
[FileManager deleteFile:documentsDirectoryGeoModel];
geoModel = [GeoModel geoModelInit];
[Utilities setGeoProjectCounter:0];
}
}
else
{
geoModel = [GeoModel geoModelInit];
}
[FileManager saveGeoModel];
return geoModel;
}
Which I then can save to the documentsDirectory as follows:
+ (BOOL)saveGeoModel
{
NSError *error = nil;
NSString *path = [self getGeoModelAbsolutePath];
[NSKeyedArchiver archiveRootObject:appDelegate.currentGeoModel toFile:path];
NSData* encodedData = [NSKeyedArchiver archivedDataWithRootObject: appDelegate.currentGeoModel];
BOOL success = [encodedData writeToFile: path options:NSDataWritingAtomic error:&error];
return success;
}
Which is always successful -- but is persistent only if I do not turn off the device! I am not making any progress with this: Any help would be much appreciated!
Thanks in advance
Tim Redfield
