What is correct form to configure UITableViewCell? - ios

Question

I am using ReusableCell in my cellForRowAtIndexPath method like that;
NSDictionary *cellData = [_cellArray objectAtIndex:indexPath.row];
static NSString *kCellID = #"homePage";
_cell = (HomePageCell*) [tableView dequeueReusableCellWithIdentifier:kCellID];
if(_cell == nil)
{
_cell = [[HomePageCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:kCellID withDictionary:cellData];
}
__weak typeof(_cell) weakSelf = _cell;
[_cell.rootImageView setImageWithURLRequest:_cell.requestImage placeholderImage:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image)
{
weakSelf.rootImageView.image=image;
} failure:nil];
and my rootImageView object is configuring. My problem is start after scrolling like that;
In Cell-1 rootImageView.image should be Image-1
In Cell-2 rootImageView.image should be Image-2
In Cell-3 rootImageView.image should be Image-3
When i starting scroll and my code is coming out if(_cell == nil), my all images turned back same image as Image-1. However, when i logged [_cellArray description], data is totally true. What is the point i missed? Why all cell images turned back Image-1 after cell is not nil?
EDIT : This is really weird, if i don't use kCellID images are loading correct. I switched _cell property to HomePageCell *cell.

Answer 1

As others have already pointed out, it looks like you’re storing _cell as an instance variable. Never do that, as each cell instance must be dequeued/created ‘on the fly’ as they are requested to be displayed onscreen.
If your UITableViewCell instance is a custom subclass (which I assume it is), you should override its -prepareForReuse method, where you should set the imageView’s image property to nil. Otherwise you could assign it a nil value in your -tableView: cellForRowAtIndexPath: implementation.
Also, because of the way that cells are quickly queued/reused/discarded, you should check that you are assigning the requested image by the time it arrives from the network to the right cell. To do so, instead of keeping a weak reference to the cell (as you’re doing), inside the network request completion block get a new reference to the cell with the desired indexPath.
In all, your implementation should look like this:
static NSString *kCellID = #"homePage”; // defined somewhere else, probably at the top of your .m file
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
HomePageCell *cell = (HomePageCell *)[tableView dequeueReusableCellWithIdentifier:kCellID];
if(cell == nil) {
cell = [[HomePageCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:kCellID withDictionary:cellData];
}
// here we reset the cell’s imageView image property to nil
// you can/should also do this inside the subclass implementation by overriding -prepareForReuse
cell.rootImageView.image = nil;
// request the remote image and set it as the imageView image property
[cell.rootImageView setImageWithURLRequest:cell.requestImage placeholderImage:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image)
{
// since the response could come back some time after the request,
// we need to get a fresh, new reference to the cell (which might
// have been dequeued and it’s no longer the same one we got before)
HomePageCell *aCell = (HomePageCell *)[tableView cellForRowAtIndexPath:indexPath];
aCell.rootImageView.image = image;
} failure:nil]
return cell;
}

Answer 2

I assume that _cell is a property on your class which is just wrong. Never store a cell as a property, it's not meant to be stored! Just create a local variable and assign the image to that. It's also not such a good idea but it should work at least. The theory of UITableView is you provide the cell once, then you don't modify it! If you want, you reload the table view, it will ask you again for the cell and then you can modify that way. You should never store any kind of pointer to a UITableViewCell or any subclass of it.

Answer 3

I assume you get that URL from cellData, in which case the problem is that you do not reset this property, so when a cell is reused you are still using the same cellData from the initWithStyle:reuseIdentifier:withDictionary: method. You should do something like:
if(_cell == nil)
{
_cell = [[HomePageCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:kCellID withDictionary:cellData];
} else {
[_cell setCellData:cellData];
}