UITableView，不可见区域中的另一个单元格带有选中标记，而触摸了可见区域中的一个

Question

This is my code, which shows a problem for 14 rows of a table view. For one screen, 6 cells are visible.

When I tapped the 2nd cell, the 10 cell also has a checkmark, tap 3rd then 11th checkmarked, 1st then 9th checkmarked, tap 1st, then 8th also checkmarked...but the grey highlight does not behave like this, only one cell can be highlighted.

If I tap a cell after one is tapped on the the same screen, the one just checkmarked will be cleared for checkmark, which makes sense. However, if after I tapped one cell and then scroll the tableview lower, I can tap a cell and it shows checkmark as well, ie the one just checked on top screen still has a checkmark. So if I scroll up and down, and tap one cell each time after I scroll to the other side, I can put a checkmark for every cell, all checkmarks are shown.

It is really weird, and I have tried a lot of ways to solve it, but seems I have some basic understanding of UITableView missing, can anyone figure it out, please? Thanks.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *ID= @"UITableViewCell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:ID];
    }

    cell.imageView.image = [UIImage imageNamed:@"earth.png"];

    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath   *)indexPath
{
    UITableViewCell *cell =[tableView cellForRowAtIndexPath:indexPath];    
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
}

-(void)tableView:(UITableView *)tableView didDeselectRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell =[tableView cellForRowAtIndexPath:indexPath];
    cell.accessoryType = UITableViewCellAccessoryNone;
}

Answer 1

You're not storing the existence/absence of your checkmark in any sort of persisted data source and showing/hiding it in cellForRowAtIndexPath . Because of this, your table is reusing your cells, and it just throws it up as it found it. So if it reuses a cell that had your checkmark accessory enabled, it shows it as enabled (because you didn't specifically disable it in cellForRow )

I would keep an NSMutableArray of selected indexPath objects. Add the indexPath in didSelectRowAtIndexPath , and remove it in didDeselectRowAtIndexPath . Then, in cellForRowAtIndexPath , check if the current indexPath exists in the array and enable the checkmark if so, disable if not.

Answer 2

Stonz2's answer is right. For example, you should create an object for table view data source and it should has a property to show is it checkmarked.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:     (NSIndexPath *)indexPath
{
    ...

    Item *item = [self.itemArray objectAtIndex:indexPath.row];
    if (item.checkmarked) {
        cell.accessoryType = UITableViewCellAccessoryCheckmark;
    } else {
        cell.accessoryType = UITableViewCellAccessoryNone;
    }

}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    [tableView deselectRowAtIndexPath:indexPath animated:NO];
    Item *tappedItem = [self.itemArray objectAtIndex:indexPath.row];
    tappedItem.checkmarked = !tappedItem.checkmarked;
    [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];


}