Problem while scrolling Table View - iphone

Question

I have the following problem while i scroll the table view:
NSCFString objectAtIndex:]: unrecognized selector sent to instance
I create NSDictionary tableContents and when i scroll it becomes deallocated.
This is my code:
- (void)viewDidLoad {
lessonsInGroup1 = [NSMutableArray array];
lessonsInGroup2 = [NSMutableArray array];
lessonsInGroup1 = [self grabRowsInGroup:#"1"];
lessonsInGroup2 = [self grabRowsInGroup:#"2"];
NSDictionary *temp =[[NSDictionary alloc]initWithObjectsAndKeys:lessonsInGroup1,#"General Information",lessonsInGroup2,#"LaTeX Examples", nil];
//[[tableContents alloc] init];
self.tableContents =temp;
[temp release];
NSLog(#"table %#",self.tableContents);
NSLog(#"table with Keys %#",[self.tableContents allKeys]);
self.sortedKeys =[[self.tableContents allKeys] sortedArrayUsingSelector:#selector(compare:)];
NSLog(#"sorted %#",self.sortedKeys);
[lessonsInGroup1 release];
[lessonsInGroup2 release];
//[table reloadData];
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
[super viewDidLoad];
}
- (NSMutableArray *) grabRowsInGroup:(NSString*)GroupID{
NSMutableArray *groupOfLessons;
groupOfLessons = [[NSMutableArray alloc] init];
char *sqlStatement;
int returnCode;
sqlite3_stmt *statement;
NSString *databaseName;
NSString *databasePath;
// Setup some globals
databaseName = #"TexDatabase.sql";
// Get the path to the documents directory and append the databaseName
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDir = [documentPaths objectAtIndex:0];
databasePath = [documentsDir stringByAppendingPathComponent:databaseName];
// Setup the database object
sqlite3 *database;
// Open the database from the users filessytem
if(sqlite3_open([databasePath UTF8String], &database) != SQLITE_OK) {
fprintf(stderr, "Error in opening the database. Error: %s",
sqlite3_errmsg(database));
sqlite3_close(database);
return;
}
sqlStatement = sqlite3_mprintf(
"SELECT * FROM Lessons WHERE LessonGroup = '%s';", [GroupID UTF8String]);
returnCode =
sqlite3_prepare_v2(database,
sqlStatement, strlen(sqlStatement),
&statement, NULL);
if(returnCode != SQLITE_OK) {
fprintf(stderr, "Error in preparation of query. Error: %s",
sqlite3_errmsg(database));
sqlite3_close(database);
return;
}
returnCode = sqlite3_step(statement);
while(returnCode == SQLITE_ROW) {
NSString *aLessonID = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 0)];
NSString *aLessonGroup = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 1)];
NSString *aLessonTopic = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 2)];
NSString *aLessonText = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 3)];
NSString *aLessonCode = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 4)];
NSString *aLessonPicture = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 5)];
/*NSLog(aLessonID);
NSLog(aLessonGroup);
NSLog(aLessonTopic);
NSLog(aLessonText);
NSLog(aLessonCode);
NSLog(aLessonPicture);*/
// Create a new busCit object with the data from the database
Lesson *lesson = [[Lesson alloc] initWithLessonID:aLessonID LessonGroup:aLessonGroup LessonTopic:aLessonTopic LessonText:aLessonText LessonCode:aLessonCode LessonPicture:aLessonPicture];
[groupOfLessons addObject:lesson];
returnCode = sqlite3_step(statement);
}
sqlite3_finalize(statement);
sqlite3_free(sqlStatement);
return [groupOfLessons autorelease];
}

Answer 1

What does your #property for tableofContents look like?
Also, you are going to run into issues with
[lessonsInGroup1 release];
[lessonsInGroup2 release];
because you are autoreleasing those in the grabRowsInGroup:
So, you don't need to call release them.

Answer 2

Looks like you are calling objectAtIndex on NSString. It should rather be some array