Saturday, June 8, 2013

UITableViewCell reuseIdentifier example in Objective C (iOS).

UITableViewCell reuseIdentifier

A string used to identify a cell that is reusable. (read-only)

@property(nonatomic, readonly, copy) NSString *reuseIdentifier

Discussion of [UITableViewCell reuseIdentifier]
The reuse identifier is associated with a UITableViewCell object that the table-view’s delegate creates with the intent to reuse it as the basis (for performance reasons) for multiple rows of a table view. It is assigned to the cell object in initWithFrame:reuseIdentifier: and cannot be changed thereafter. A UITableView object maintains a queue (or list) of the currently reusable cells, each with its own reuse identifier, and makes them available to the delegate in the dequeueReusableCellWithIdentifier: method.

UITableViewCell reuseIdentifier example.
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

if (cell == nil)
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    NSLog(@"new one");
    NSLog(@"old one");

Example of [UITableViewCell reuseIdentifier].
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
    static NSString *cellIdentifier = @"Cell";
    CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    if(cell == nil)
        cell = [[CustomCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
    TextFieldFormElement *item = [self.formItems objectAtIndex:indexPath.row];
    cell.labelField.text = item.label;
    return cell;

UITableViewCell reuseIdentifier example.
- (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)indexPath
  UITableViewCell *cell;
  UILabel *label = nil;

  cell = [tv dequeueReusableCellWithIdentifier:@"Cell"];
  if (cell == nil)
    cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:@"Cell"] autorelease];

    label = [[UILabel alloc] initWithFrame:CGRectZero];
    [label setLineBreakMode:UILineBreakModeWordWrap];
    [label setMinimumFontSize:FONT_SIZE];
    [label setNumberOfLines:0];
    [label setFont:[UIFont systemFontOfSize:FONT_SIZE]];
    [label setTag:1];

    [[label layer] setBorderWidth:2.0f];

    [[cell contentView] addSubview:label];

  NSString *text = [items objectAtIndex:[indexPath row]];

  CGSize constraint = CGSizeMake(CELL_CONTENT_WIDTH - (CELL_CONTENT_MARGIN * 2), 20000.0f);

  CGSize size = [text sizeWithFont:[UIFont systemFontOfSize:FONT_SIZE] constrainedToSize:constraint lineBreakMode:UILineBreakModeWordWrap];

  if (!label)
    label = (UILabel*)[cell viewWithTag:1];

  [label setText:text];

  return cell;

End of UITableViewCell reuseIdentifier example article.