How to use Reusable Cells in uitableview for IOS

Question

Ok. I cant seem to get a firm understanding on how tableviews work. Would someone please explain to me how cells are reused in tableviews especially when scrolling? One of t

Answer 1

I am assuming you are doing this via Storyboard and since you haven't created your button via the Interface Builder, you need to check if the cell that is being re-used already has the button or not.
As per your current logic, you are creating a new button instance ever time the cell reappears.

I'd suggest the following:

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

    //following is required when using XIB but not needed when using Storyboard
    /*
     if (cell == nil) {
         cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
     }
     */
    //Reason:
    //[1] When using XIB, dequeueReusableCellWithIdentifier does NOT create a cell so (cell == nil) condition occurs
    //[2] When using Storyboard, dequeueReusableCellWithIdentifier DOES create a cell and so (cell == nil) condition never occurs

    //check if cell is being reused by checking if the button already exists in it
    UIButton *myButton = (UIButton *)[cell.contentView viewWithTag:100];

    if (myButton == nil) {
        myButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [myButton setFrame:CGRectMake(14.0,10.0,125.0,25.0)];
        [myButton setTag:100]; //the tag is what helps in the first step
        [myButton setTitle:@"Like" forState:UIControlStateNormal];
        [myButton setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
        [myButton addTarget:self action:@selector(tapped:andEvent:) forControlEvents:UIControlEventTouchUpInside];
        [cell.contentView addSubview:myButton];

        NSLog(@"Button created");
    }
    else {
        NSLog(@"Button already created");
    }

    if ([likeState[indexPath.row] boolValue]) {
        [myButton setTitle:@"Unlike" forState:UIControlStateNormal];
    }
    else {
        [myButton setTitle:@"Like" forState:UIControlStateNormal];
    }

    return cell;
}

---

-(void)tapped:(UIButton *)sender andEvent:(UIEvent *)event
{
    //get index
    NSSet *touches = [event allTouches];
    UITouch *touch = [touches anyObject];
    CGPoint currentTouchPosition = [touch locationInView:self.tableView];
    NSIndexPath *indexPath = [self.tableView indexPathForRowAtPoint:currentTouchPosition];

    //toggle "like" status
    if ([likeState[indexPath.row] boolValue]) {
        [likeState replaceObjectAtIndex:indexPath.row withObject:@(0)];
        [sender setTitle:@"Like" forState:UIControlStateNormal];
    }
    else {
        [likeState replaceObjectAtIndex:indexPath.row withObject:@(1)];
        [sender setTitle:@"Unlike" forState:UIControlStateNormal];
    }
}