iphone - Reusable TableView header views

Question

For performance sake it is usual to reuse UITableView' cells. Is there a way to do the same thing with TableView header' views? I am talking about the ones that are returned with delegate's method:

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section

I tried to do the following which doesn't seem to be working as expected:

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    static NSString *CellIdentifier = @"Header";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier: CellIdentifier];
    if (cell == nil) {
        cell = [self getHeaderContentView: CellIdentifier];
    }
    return cell;
}

Is there a way to reuse header' views?

Answer 1

The reason Apple built in the ability to reuse tableview cells is because while the tableview may have many rows, only a handful are displayed on screen. Instead of allocating memory for each cell, applications can reuse already existing cells and reconfigure them as necessary.

First off, header views are just UIViews, and while UITableViewCell is a subclass of UIView, they are not intended to be placed as the view of a section header.

Further, since you generally will have far fewer section headers than total rows, there's little reason to build a reusability mechanism and in fact Apple has not implemented one for generic UIViews.

Note that if you are just setting a label to the header, you can use -(NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section instead.

For something more custom, such as a label with red text (or a button, image, etc), you can do something like this:

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
  UIView *headerView = [[[UIView alloc] initWithFrame:CGRectMake(0,0, 320, 44)] autorelease];
  UILabel *label = [[[UILabel alloc] initWithFrame:headerView.frame] autorelease];
  label.textColor = [UIColor redColor];
  label.text = [NSString stringWithFormat:@"Section %i", section];

  [headerView addSubview:label];
  return headerView;
}