didSelectRowAtIndexPath selecting more than one row at a time

Question

I have a UITableView populated with 27 rows. I am trying to change the accessoryType of the selected cell. I do that in the didSelectRowAtInd

Answer 1

Remember every cell in the table view is actually the same object being re-used. If you don't set the accessory type every time cellForRowAtIndexPath is called, when new cells scroll onto the screen they're going to all have the same accessory." - daxnitro

This is where I got caught. I had mine set up so that in my "cellForRowAtIndexPath" function, I would only change the accessory for those specified in my array of checked cells, when what I should have done was update the accessory for all cells in the table.

In other words:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
//normal set up

    //retrieve key
    NSUserDefaults *settings = [NSUserDefaults standardUserDefaults];
    id obj = [settings objectForKey:@yourKey];

    //if the array is not populated, keep standard format for all cells
    if (obj == nil){
        selectedStyles = [[NSMutableArray alloc] initWithObjects:nil];
        [cell setAccessoryType:UITableViewCellAccessoryNone];  //no check mark
        [cell textLabel].textColor = [[UIColor alloc] initWithRed:0.0/255 green:0.0/255 blue:0.0/255 alpha:1.0];  //keep black color

    }
    //else retrieve information from the array and update the cell's accessory
    else{
        //if the cell is in your array, add a checkbox
        [cell setAccessoryType:UITableViewCellAccessoryCheckmark];  //add check box
        [cell textLabel].textColor = [[UIColor alloc] initWithRed:50.0/255 green:79.0/255 blue:133.0/255 alpha:1.0];  //change color of text label
        //if the cell is not in your array, then keep standard format
        [cell setAccessoryType:UITableViewCellAccessoryNone];  //no check mark
        [cell textLabel].textColor = [[UIColor alloc] initWithRed:0.0/255 green:0.0/255 blue:0.0/255 alpha:1.0];  //keep black color

Hope this helps!

Answer 2

Here's one way to do it:

- (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 setText:[NSString stringWithFormat:@"Row %d", indexPath.row]];

    NSIndexPath* selection = [tableView indexPathForSelectedRow];
    if (selection && selection.row == indexPath.row) {
        cell.accessoryType = UITableViewCellAccessoryCheckmark; 
    } else {
        cell.accessoryType = UITableViewCellAccessoryNone;  
    }

    // Configure the cell.
    return cell;
}

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

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

Remember every cell in the table view is actually the same object being re-used. If you don't set the accessory type every time cellForRowAtIndexPath is called, when new cells scroll onto the screen they're going to all have the same accessory.

Multiple Select

For multiple selection it's a bit more complicated.

Your first option: Undocumented API

Note that this only works when the table's in editing mode. Set each cell's editing style to the undocumented UITableViewCellEditingStyleMultiSelect. Once you do that, you can get the table view's selection via an undocumented member of UITableView: indexPathsForSelectedRows. That should return an array of the selected cells.

You can expose this bit of functionality by putting this in a header:

enum {
    UITableViewCellEditingStyleMultiSelect = 3,
};

@interface UITableView (undocumented)
- (NSArray *)indexPathsForSelectedRows;
@end

Then set the editing style for each cell like so:

- (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath {
    return UITableViewCellEditingStyleMultiSelect;
}

When the table is in editing mode you'll see the multi-select controls on your cells.

To look through other undocumented API, you can use the nm command line utility like this:

nm /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk/System/Library/Frameworks/UIKit.framework/UIKit

Your second option: Manage the selection yourself

Have your UITableView subclass contain an array that indicates which cells are selected. Then in cellForRowAtIndexPath, configure the cell's appearance using that array. Your didSelectRowAtIndexPath method should then look something like this:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    if ([tableView indexPathIsSelected:indexPath]) {
        [tableView removeIndexPathFromSelection:indexPath];
    } else {
        [tableView addIndexPathToSelection:indexPath];
    }
    // Update the cell's appearance somewhere here
    [tableView deselectRowAtIndexPath:indexPath animated:NO];
}

This assumes you create indexPathIsSelected, removeIndexPathFromSelection, and addIndexPathToSelection methods in your UITableView subclass. These methods should do exactly what their names imply: Add, remove, and check for index paths in an array. You wouldn't need a didDeselectRowAtIndexPath implementation if you go with this option.