Question

In my “viewWillAppear” callback I attempt to populate a UITableViewController with data from SQLite database for the user to see.

However, what I noticed was if I switch to another tab, commit a new row of data into SQLite and switch back to the UITableViewController it does not update with the new row I just added to the database. I have to quit out of the app completely and navigate back to the UITableViewController in order to see the new row reflected on the table view.

How do I get around this problem (i.e. how do I force always showing the very latest information in SQLite on the UITableViewController after switching back and forth a bunch of times?)

Would appreciate all / any advice.

Here is the code:

- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
NSLog(@"viewwillappear");
//[[self tableView] reloadData];
int rc=-1;
if (databasePath == nil) {
    NSLog(@"database path is NIL. Trying to set it");
    databaseName = @"mymemories.sqlite";
    NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDir = [documentPaths objectAtIndex:0];
    databasePath = [documentsDir stringByAppendingPathComponent:databaseName];
    return;
}
rc = sqlite3_open([databasePath UTF8String], &database);
if(rc == SQLITE_OK) {
    memoriesArray = [[NSMutableArray alloc]init ];
    sqlite3_stmt *statement = nil;


    NSString *fullQuery = @"SELECT * FROM memories";

    const char *sql = [fullQuery UTF8String];

    if(sqlite3_prepare_v2(database, sql, -1, &statement, NULL)!=SQLITE_OK)
        NSAssert1(0, @"Error preparing statement '%s'", sqlite3_errmsg(database));
    else
    {
        while(sqlite3_step(statement) == SQLITE_ROW)
        {
            NSString *place= [NSString stringWithUTF8String:(const char*)sqlite3_column_text(statement, 4)];
            //[User setName:[NSString stringWithUTF8String:(const char*)sqlite3_column_text(statement, 1)]];
            //[User setAge:[NSString stringWithUTF8String:(const char*)sqlite3_column_text(statement, 2)]];

            [memoriesArray addObject:place];
            //[currentUser release];
        }
    }
    sqlite3_finalize(statement);
    sqlite3_close(database);
}

}

Also in case this is relevant, here is the code that commits to the SQLite database:

    NSData * blob = [NSData dataWithContentsOfURL:recordedTmpFile];
int rc=-1;
rc = sqlite3_open([databasePath UTF8String], &database);

if(rc == SQLITE_OK) {
    sqlite3_exec(database, "BEGIN", 0, 0, 0);


    NSLog(@"Connected To: %@",databasePath);
    sqlite3_stmt *updStmt =nil; 
    const char *sql = "INSERT INTO memories (data,place) VALUES (?,?);";

    rc = sqlite3_prepare_v2(database, sql, -1, &updStmt, NULL);

    if(rc!= SQLITE_OK)
    {
        NSLog(@"Error while creating update statement:%@", sqlite3_errmsg(database));
    }
    sqlite3_bind_text( updStmt, 2, [[tags text] UTF8String], -1, SQLITE_TRANSIENT);
    rc = sqlite3_bind_blob(updStmt, 1, [blob bytes], [blob length] , SQLITE_BLOB);

    if((rc = sqlite3_step(updStmt)) != SQLITE_DONE)
    {
        NSLog(@"Error while updating: %@", sqlite3_errmsg(database));
        sqlite3_reset(updStmt);
    } 

    sqlite3_exec(database, "COMMIT", 0, 0, 0);
    //rc = sqlite3_reset(updStmt);

    sqlite3_close(database);

}

Answer 1

As an extension of an explanation of Darren’s answer.

First off his answer is correct.
Secondly you need to use an NSMutableArray to ensure consistency, this is where you are going wrong by not updating it as you should

The steps you should be taking to ensure consistency are the following:

Loading Data into Table

• In viewDidLoad, call your SQL statement and load it into your array
• in viewWillAppear ensure that your array contains data, if not display a notice that no results were returned

Saving Data into Database

• Update the change to the array (or datasource)
• Update the Database with the updated datasource to ensure consistency
• Update the table with one of the 4 UITableView reloading methods

Using the NSMArray to ensure consistency between updates and app loads is fairly common practise has be recommended to me in the past by fellow co workers with decades of experience.

Note:
You will need to synchronise the datasource to ensure that 1 thread is accessing it at any 1 time otherwise you will get a crash.