UITableView not scrolling smoothly…(iPhone SDK) ..!

Question

UITableView not scrolling smoothly...(iPhone SDK) ..!!

I have implemented UITableView DataSource and Delegate methods in an individual separate classes.(one for delegate and one for datasource) in main program i write only:

//assume that all objects are allocated 
ObjTableView.dataSource=ObjDataSource;
ObjTableView.delegate = ObjDelegate;
[self.view addSubView: ObjTableView];

when i run this code , UITable view appears but when i try to scroll it, it doesn't scroll smoothly. I have also checked that UITableViewCell doesn't redraw once the cell is initialized.

can any one tell me why this happens ? How can i solve this problem ??

From comments:

ListDataSource *ObjListDataSource = [[ListDataSource alloc]initWithArray:[[sender object] valueForKey:@"List"]]; 
ListDelegate *ObjListDelegate = [[ListDelegate alloc]initWithArray:[[sender object] valueForKey:@"List"]];
tblList = [[UITableView alloc]initWithFrame:CGRectMake(0, 0, 320, 460)];  
tblList.dataSource = ObjListDataSource; tblList.delegate = ObjListDelegate; 
[self.view addSubview:tblList]; [tblShopList release];

More from comments:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 
    NSString *CellIdentifier = [NSString stringWithFormat:@"%i",indexPath.row]; 
    UITableViewCell *cell = (UITableViewCell*)[tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithFrame:CGRectMake(0,0,320,100) reuseIdentifier:CellIdentifier] autorelease]; 
        //custom cell code 
    } 
    return cell; 
}

More Information:

I have used NSNotification which notifies to current class when parsing is complete, after receiving notification , current class method calls DataSource, Delegate methods (which is defined in a separate class file).

So UItableViewCell customization (which is in ListDataSource) and table view(in current class) both are in different classes.

Answer 1

A problem is

NSString *CellIdentifier = [NSString stringWithFormat:@"%i",indexPath.row]; 

The id needs to be the same for all cells of the same class, otherwise you never reuse them. As you can see in most examples, it is indeed a constant in most (all?) cases.

Little explaination on the reuseIdentifier: every time a cell gets out of screen, you can reuse it instead of creating a new one. To reuse it, you need a cell in queue with the same identifier as the one you pass to dequeueReusableCellWithIdentifier . The way you did, the cells are never reused, because each id is unique (they may or may not be reused in case a row reappears on screen, depending on queue size, which is not configurable AFAIK). This is why personalization of the cell should happen OUTSIDE the " cell == nil " block. Long story short, you are using the reuseIdentifier not as intendend.

Answer 2

I think Michele is correct, but I would also add that it looks like you are doing your cell customization where the cell gets created. What you should be doing is something more like this:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    NSString *CellIdentifier = @"CellIdentifier";
    UITableViewCell *cell = (UITableViewCell)[tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithFrame:CGRectMake(0,0,320,100) reuseIdentifier:CellIdentifier] autorelease]; 
        //custom REUSABLE cell code here, e.g. text color, etc. 
    }

    NSString *cellText = [dataArray objectAtIndex:indexPath.row]; //assuming you have a simple array for your data

    cell.textLabel.text = cellText;

    return cell; 
}

I would also add that I'm not sure why you are able to run the app with the code you have here, since UITableViewCell cell = ... is an invalid initializer. It should be UITableViewCell *cell = ... .

It would be helpful to see how you are customizing your cell, since without that it's hard to see what's happening.