Calling two times a function of a static variable? - objective-c

Question

I have this class containing a static variable "database" which represent a database realized with sqlite and a function getAllShop which task is recalling all the data that are stored in the db and filling them into a mutable array
#define kFilename #"negozi.sqlite"
#implementation ShopDatabase
static ShopDatabase *database;
+(ShopDatabase *)database{
if (database==nil) {
database = [[ShopDatabase alloc] init];
return database;
}
}
- (id)init
{
self = [super init];
if (self) {
// Create the path to the database in the Documents directory for the bundle itself is not writable
NSArray *pathsToDocuments = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [pathsToDocuments objectAtIndex:0];
databasePath = [documentsDirectory stringByAppendingPathComponent:kFilename];
if (![[NSFileManager defaultManager] isReadableFileAtPath:databasePath]) {
if ([[NSFileManager defaultManager] copyItemAtPath:yourOriginalDatabasePath toPath:databasePath error:NULL] != YES)
NSAssert2(0, #"Fail to copy database from %# to %#", yourOriginalDatabasePath, databasePath);
}
// --- open db
if(sqlite3_open([databasePath UTF8String], &database) != SQLITE_OK){
NSLog(#"Failed to open database");
}else {
NSLog(#"Database opened");
}
}
return self;
}
- (NSMutableArray *) getAllShops{
// ------ read all the db
NSMutableArray *returnArray=[[NSMutableArray alloc] init];
NSString *query= #"SELECT * FROM negozio";
sqlite3_stmt *statement;
if (sqlite3_prepare_v2(database, [query UTF8String], -1, &statement, NULL) == SQLITE_OK){
NSLog(#"Prepared database");
while (sqlite3_step(statement)==SQLITE_ROW) {
int uniqueId = sqlite3_column_int(statement, 0);
NSMutableString *nome = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 1)];
ShopInfo *info= [[ShopInfo alloc] initWithUniqueId:uniqueId nome:nome];
[returnArray addObject:info];
}
sqlite3_finalize(statement);
}
return returnArray;
}
#end
When i have to take data from the database from another class i do this, calling the getAllShop and all goes well. In this way i have all the data of the db into my array shopinfo:
NSMutableArray *shopInfo=[[ShopDatabase database] getAllShops];
Now, my database contains data that i need to use to fill TWO table view, so i need to execute this TWO times: one time in the class representing the first table view and one in the second. When i do this in the first view all goes well, but when i do the same the second time, Xcode give me a exc bad access error. I tried executing the code two times in the same class and this is what i get
2012-05-11 13:06:54.897 Shopping Mall[11333:707] -[NegozioPartenza getAllShops]: unrecognized selector sent to instance 0x14b8c0
2012-05-11 13:06:54.899 Shopping Mall[11333:707] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NegozioPartenza getAllShops]: unrecognized selector sent to instance 0x14b8c0'
*** First throw call stack:
(0x33ad188f 0x325c3259 0x33ad4a9b 0x33ad3915 0x33a2e650 0xa4141 0x35727e33 0x3574c629 0x35710d7d 0x357d34dd 0x3571955d 0x3571940b 0x357d34a3 0x35788873 0x357881b7 0x357d1d89 0x357d04eb 0x3582b82b 0x33a2b3fd 0x35709faf 0x35709f6b 0x35709f49 0x35709cb9 0x3570a5f1 0x35708ad3 0x357084c1 0x356ee83d 0x356ee0e3 0x32fa622b 0x33aa5523 0x33aa54c5 0x33aa4313 0x33a274a5 0x33a2736d 0x32fa5439 0x3571ce7d 0xa2515 0xa24c0)
terminate called throwing an exception(lldb)
I am a newbie to objective C so i can't manage to understand what's the point. How can i call two times a function on a static variable? Thank you.
Edit: maybe calling the [ShopDatabase database] activate a second time the constructor of initializazione making mess? When i say that a variable is static it mean there's only one instance of it for every object of that class, right? So how i can access that unique instance after creating it the first time? I think i'm messing up what happen when you use a static variable...

Answer 1

You don't have a valid return on the second call.
+(ShopDatabase *)database{
if (database==nil) {
database = [[ShopDatabase alloc] init];
return database;
}
}
On the second call database is not nil and you don't return anything. You should be getting a warning that not all control paths return a value.
Here is the proper way.
+(ShopDatabase *)database{
if (database==nil) {
database = [[ShopDatabase alloc] init];
}
return database;
}

Answer 2

Somewhere after your first call, database is being released. Subsequently, an object of type NegozioPartenza is being created at the same location. The second call to [ShopDatabase database] returns this object, and you then send -getAllShops to that object, which obviously doesn't implement that method.