Question

I have multiple objects, each with a series of attributes. I’d like the user to select two objects and then the app will display a comparison of the respective object’s attributes. I’m having difficulty deciding how best to select the two objects. I would use a UITableView, but how to select two cells before proceeding? Alternatively, I could display UIButtons, but again, how best to select two before proceeding? Perhaps there is another way that isnt occuring to me.

Ideas appreciated.

Answer 1

Make sure your tableView allows selections:

myTableView.allowsSelection = YES;

Define two properties two store the first and second selection index paths:

@property (nonatomic, retain) NSIndexPath *firstSelection;
@property (nonatomic, retain) NSIndexPath *secondSelection;

Set the selection whenever the user selects a row. In this example, I use FIFO approach to the selections. In addition, if there are two selections already made, show the object attributes:

- (void)tableView:(UITableView *)tableView 
                   didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

   // push the selections up each time. The selected items will always be the
   // last two selections
   self.firstSelection = self.secondSelection;
   self.secondSelection = indexPath;

   // if both selections are not nil, two selections have been made.
   if (self.firstSelection && self.secondSelection)
      [self showComparisonOfObject:self.firstSelection
                        withObject:self.secondSelection];
}

Finally, use a checkmark accessory on the selected rows:

- (UITableViewCell *)tableView:(UITableView *)tableView 
         cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
   static NSString *CellIdentifier = @"Cell";
   UITableViewCell *cell = 
                    [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

   if (cell == nil) {
       cell = [[[UITableViewCell alloc] 
                 initWithStyle:UITableViewCellStyleDefault
                 reuseIdentifier:CellIdentifier] autorelease];
   }

   cell.textLabel.text = someTextYouDefine;
   cell.textLabel.textAlignment = UITextAlignmentCenter;
   cell.selectionStyle = UITableViewCellSelectionStyleNone;

   // this is where the magic happens
   BOOL cellSelected = indexPath == self.firstSelection || 
                       indexPath == self.secondSelection; 

   cell.accessoryType = cellSelected ? UITableViewCellAccessoryCheckmark :
                                       UITableViewCellAccessoryNone;

   // the following two lines ensure that the checkmark does not cause
   // the label to be off-center
   cell.indentationLevel = cellSelected ? 1 : 0;
   cell.indentationWidth = 20.0f;

   return cell;
}