Detecting which UIButton was pressed in a UITableView

Question

Hi,

I have a UITableView with 5 UITableViewCells. Each cell contains a UIButton which is set up as follows:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     NSString *identifier = @"identifier";
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
     if (cell == nil) {
         cell = [[UITableView alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
         [cell autorelelase];

         UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(10, 5, 40, 20)];
         [button addTarget:self action:@selector(buttonPressedAction:) forControlEvents:UIControlEventTouchUpInside];
         [button setTag:1];
         [cell.contentView addSubview:button];

         [button release];
     }

     UIButton *button = (UIButton *)[cell viewWithTag:1];
     [button setTitle:@"Edit" forState:UIControlStateNormal];

     return cell;
}

My question is this: in the buttonPressedAction: method, how do I know which button has been pressed. I've considered using tags but I'm not sure this is the best route. I'd like to be able to somehow tag the indexPath onto the control.

- (void)buttonPressedAction:(id)sender
{
    UIButton *button = (UIButton *)sender;
    // how do I know which button sent this message?
    // processing button press for this row requires an indexPath. 
}

What's the standard way of doing this?

Edit:

I've kinda solved it by doing the following. I would still like to have an opinion whether this is the standard way of doing it or is there a better way?

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     NSString *identifier = @"identifier";
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
     if (cell == nil) {
         cell = [[UITableView alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
         [cell autorelelase];

         UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(10, 5, 40, 20)];
         [button addTarget:self action:@selector(buttonPressedAction:) forControlEvents:UIControlEventTouchUpInside];
         [cell.contentView addSubview:button];

         [button release];
     }

     UIButton *button = (UIButton *)[cell.contentView.subViews objectAtIndex:0];
     [button setTag:indexPath.row];
     [button setTitle:@"Edit" forState:UIControlStateNormal];

     return cell;
}

- (void)buttonPressedAction:(id)sender
{
    UIButton *button = (UIButton *)sender;
    int row = button.tag;
}

What's important to note is that I can't set the tag in the creation of the cell since the cell might be dequeued instead. It feels very dirty. There must be a better way.

Answer 1

I always use tags.

You need to subclass the UITableviewCell and handle the button press from there.

Answer 2

I would use the tag property like you said, setting the tag like so:

[button setTag:indexPath.row];

then getting the tag inside of the buttonPressedAction like so:

((UIButton *)sender).tag

Or

UIButton *button = (UIButton *)sender; 
button.tag;

Answer 3

you can use the tag pattern:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     NSString *identifier = @"identifier";
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
     if (cell == nil) {
         cell = [[UITableView alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
         [cell autorelelase];

         UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(10, 5, 40, 20)];
         [button addTarget:self action:@selector(buttonPressedAction:) forControlEvents:UIControlEventTouchUpInside];
         [button setTag:[indexPath row]]; //use the row as the current tag
         [cell.contentView addSubview:button];

         [button release];
     }

     UIButton *button = (UIButton *)[cell viewWithTag:[indexPath row]]; //use [indexPath row]
     [button setTitle:@"Edit" forState:UIControlStateNormal];

     return cell;
}

- (void)buttonPressedAction:(id)sender
{
    UIButton *button = (UIButton *)sender;
    //button.tag has the row number (you can convert it to indexPath)
}

Answer 4

I'd also use tags, but when reusing your cell in -cellForRowAtIndexPath method you need to set button's tag each time to the actual row value.
To obtain the button you can iterate through your cell subviews and find it (it may be not optimal way though)

Edit: I've got an idea about may be more elegant methods (have not tested that, but I think it should work):

- (void)buttonPressedAction:(id)sender
{
   UIButton *button = (UIButton *)sender;
   (UITableViewCell*)cell = [button superview];
   int row = [myTable indexPathForCell:cell].row;
}

Or you can set tag for cell each time, but not UIButton. Your action will look then:

- (void)buttonPressedAction:(id)sender
{ 
   UIButton *button = (UIButton *)sender;
   int row = [button superview].tag;
}

Edit2: In Apple's Accessory sample the following method is used: UIButton touch handler set to receive information about touch event:

[button addTarget:self action:@selector(checkButtonTapped:event:) forControlEvents:UIControlEventTouchUpInside];

Then in touch handler touch coordinate retrieved and index path is calculated from that coordinate:

- (void)checkButtonTapped:(id)sender event:(id)event
{
    NSSet *touches = [event allTouches];
    UITouch *touch = [touches anyObject];
    CGPoint currentTouchPosition = [touch locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint: currentTouchPosition];
    if (indexPath != nil)
    {
     ...
    }
}

Answer 5

Though I like the tag way... if you don't want to use tags for whatever reason, you could create a member NSArray of premade buttons:

NSArray* buttons ;

then create those buttons before rendering the tableView and push them into the array.

Then inside of the tableView:cellForRowAtIndexPath: function you can do:

UIButton* button = [buttons objectAtIndex:[indexPath row] ] ;
[cell.contentView addSubview:button];

Then in the buttonPressedAction: function, you can do

- (void)buttonPressedAction:(id)sender {
   UIButton* button = (UIButton*)sender ;
   int row = [buttons indexOfObject:button] ;
   // Do magic
}

Answer 6

Found a nice solution to this problem elsewhere, no messing around with tags on the button:

- (void)buttonPressedAction:(id)sender {

NSSet *touches = [event allTouches];
UITouch *touch = [touches anyObject];
CGPoint currentTouchPosition = [touch locationInView:self.tableView];
NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint: currentTouchPosition];

do stuff with the indexPath...
}

Answer 7

I found the method of using the superview's superview to obtain a reference to the cell's indexPath worked perfectly. Thanks to iphonedevbook.com (macnsmith) for the tip link text

-(void)buttonPressed:(id)sender {
 UITableViewCell *clickedCell = (UITableViewCell *)[[sender superview] superview];
 NSIndexPath *clickedButtonPath = [self.tableView indexPathForCell:clickedCell];
...

}

Answer 8

Am I missing something? Can't you just use sender to identify the button. Sender will give you info like this:

<UIButton: 0x4b95c10; frame = (246 26; 30 30); opaque = NO; tag = 104; layer = <CALayer: 0x4b95be0>>

Then if you want to change the properties of the button, say the background image you just tell sender:

[sender setBackgroundImage:[UIImage imageNamed:@"new-image.png"] forState:UIControlStateNormal];

If you need the tag then ACBurk's method is fine.

Answer 9

// how do I know which button sent this message?
// processing button press for this row requires an indexPath.

Pretty straightforward actually:

- (void)buttonPressedAction:(id)sender
{
    UIButton *button = (UIButton *)sender;
    CGPoint rowButtonCenterInTableView = [[rowButton superview] convertPoint:rowButton.center toView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:rowButtonCenterInTableView];
    MyTableViewItem *rowItem = [self.itemsArray objectAtIndex:indexPath.row];
    // Now you're good to go.. do what the intention of the button is, but with
    // the context of the "row item" that the button belongs to
    [self performFooWithItem:rowItem];
}

Working well for me :P

if you want to adjust your target-action setup, you can include the event parameter in the method, and then use the touches of that event to resolve the coordinates of the touch. The coordinates still need to be resolved in the touch view bounds, but that may seem easier for some people.