UISwitch untoggling on scroll of a UITableView - iphone

Question

I have a UITableView with a UISwitch as the accessoryView. My problem is that if I toggle one of the switches then scroll so the switch it out of view it returns to its previous state.
Please see video.
Does anyone know why this might be and how to solve it?
Here is the code that adds the switch view and deals with its action.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *CellIdentifier = #"POICell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier ];
//set the cell text to the
cell.textLabel.text = [self.catNames objectAtIndex:[indexPath row]];
NSString *toggle = [self.toggleArray objectAtIndex:[indexPath row]];
//add switch
cell.selectionStyle = UITableViewCellSelectionStyleNone;
//create an instance of the database oject
DataBase * dataBase = [[DataBase alloc] init];
//open the database connection
[dataBase openDB];
NSString *imageName = [dataBase getPinImageNameFromCatID:[self.catIDs objectAtIndex:[indexPath row]]];
//get the root file path for the images
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [NSString stringWithFormat:#"%#/pinImages/%#",documentsDirectory, imageName];
//add image
NSURL *imageURL = [NSURL fileURLWithPath:filePath];
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
UIImage *image = [UIImage imageWithData:imageData];
cell.imageView.image = image;
NSLog(#"%#",[self.catIDs objectAtIndex:[indexPath row]]);
UISwitch *switchView = [[UISwitch alloc] initWithFrame:CGRectZero];
cell.accessoryView = switchView;
[switchView addTarget:self action:#selector(switchChanged: ) forControlEvents:UIControlEventValueChanged];
if ([toggle isEqualToString: #"OFF"]) {
[switchView setOn:NO animated:NO];
}else{
[switchView setOn:YES animated:NO];
}
return cell;
}
- (void) switchChanged:(id)sender {
//get the switch that it was sent from
UISwitch *switchInCell = (UISwitch *)sender;
//get the cell it was sent from
UITableViewCell * cell = (UITableViewCell *) switchInCell.superview;
//get the row it was sent from
NSIndexPath * indexpath = [self.inputTableView indexPathForCell:cell];
//cast the indexpath to int
NSInteger variable = indexpath.row;
//set the filter as off in the user defualts.
[self.filterDic setValue:switchInCell.on ? #"ON" : #"OFF" forKey:[self.catIDs objectAtIndex:variable]];
//store the newdic in the user defualts
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
//save the dic to user defaults
[prefs setObject:self.filterDic forKey:#"pinFilters"];
}
Thanks for any help.

Answer 1

There are two issues with your code (at least :)
Let me start with the one that is confusing you.
You set the status of each witch based on toggle. And the value of toggle is tanken from an array self.toggleArray.
Fine so far.
But when a value changes and the action switchChanged is called then you update self.filterDic but you do not update self.toggleView.
And this causes the problem:
Next time when a cell becomes visible cellForRowAtIndexPath is called again and will set the value based on toggle wich is based on self.toggleArray. And that still has the old values in it ... you see?
You are making this mistake probably because you have not yet fully understood the cell recycle mechanism. And that is probably what causes the second issue that I identified. Let me try to explain.
iOS or cocoa respectively tries to allocate as view cell objects as nessessary. That means that a cell wich scrolls off the creen is added to a pool from which it can be re-used the next time when a (similar) sell is required. So each time when there is a need for a new cell (one that becomes visible) cellForRowAtIndexPath is called. Wihin that you fetch a cell using dequeueReusableCellWithIdentifier. If there is a cell in that pool that was initialized with the same re-use identfier then that one (or one of those) is returned to the caller.
In recent iOS (respectively SDK versions) versions a new cell will be allocated and returned if none of these cells exists. (And that is why Murali's suggestion would not work perfectly either)
In older versions you had to check cell for nil and alloc/init a new on in those cases.
After that you freely allocate new subview objects regardless whether the cell was re-cycled and already has those subviews or not. Then you add and add and add the same subviews again and again.
How can you solve this? There are, as usual, several ways of dealing with that:
First - Check whether the cell was re-used or not. Just check if the Switch is already there or not. For doing that you could tag it with some value different from 0 and fetch the subview with this tag. If you dont't get it then the cell is new and you have to create all the additional subvies.
Second - You could always erase all subviews from the cell right after fetching the cell with dequeueReusableCellWithIdentifier. That is the easiest solultion because you do not have to change mutch to your existing code. It is not the most performant solution though.
Third - The most elegant solution is probably to subclass UITableViewCell every time when you want to add custom elements to a cell. In that case its init method would be called only once upon creation (and not upon re-usage) and there you can programmatically add all the custom subviews. You can, of course, design the cell and add all subviews in IB as you can with every UIView object. Witin cellForRowAtIndexPath you would only have to care for setting the appropriate values.

Answer 2

Perhaps your cells are being recycled.
Have a look at the accepted answer here:
iphone : uitableview : contents of a cell change on scrolling

Answer 3

Please use this method..
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *CellIdentifier = #"POICell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
UISwitch *switchView;
if (cell == nil)
{
cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier ];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
switchView = [[UISwitch alloc] initWithFrame:CGRectMake(0, 0, 100, 30)];//Change the frame
cell.accessoryView = switchView;
}
//set the cell text to the
cell.textLabel.text = [self.catNames objectAtIndex:[indexPath row]];
NSString *toggle = [self.toggleArray objectAtIndex:[indexPath row]];
//add switch
//create an instance of the database oject
DataBase * dataBase = [[DataBase alloc] init];
//open the database connection
[dataBase openDB];
NSString *imageName = [dataBase getPinImageNameFromCatID:[self.catIDs objectAtIndex:[indexPath row]]];
//get the root file path for the images
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *filePath = [NSString stringWithFormat:#"%#/pinImages/%#",documentsDirectory, imageName];
//add image
NSURL *imageURL = [NSURL fileURLWithPath:filePath];
NSData *imageData = [NSData dataWithContentsOfURL:imageURL];
UIImage *image = [UIImage imageWithData:imageData];
cell.imageView.image = image;
NSLog(#"%#",[self.catIDs objectAtIndex:[indexPath row]]);
[switchView addTarget:self action:#selector(switchChanged: ) forControlEvents:UIControlEventValueChanged];
if ([toggle isEqualToString: #"OFF"]) {
[switchView setOn:NO animated:NO];
}else{
[switchView setOn:YES animated:NO];
}
return cell;
}