How to properly reuse a cell in UITableView - ios

Question

I'm a newbie. I am using this code to create a UITableViewCell but when I reload the table the button's image is not always correct, although all labels work fine. I don't know why. How can I fix this issue?
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [_tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
UILabel *FileNameLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 0, 100, 30)];
FileNameLabel.tag = 1000;
FileNameLabel.backgroundColor = [UIColor clearColor];
FileNameLabel.font = [UIFont fontWithName:#"Helvetica" size:16];
FileNameLabel.font = [UIFont boldSystemFontOfSize:16];
FileNameLabel.textColor = [UIColor blackColor];
[cell.contentView addSubview: FileNameLabel];
[FileNameLabel release];
UILabel *UploadTimeLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 20, 150, 25)];
UploadTimeLabel.tag = 2000;
UploadTimeLabel.backgroundColor = [UIColor clearColor];
UploadTimeLabel.font = [UIFont fontWithName:#"Helvetica" size:12];
UploadTimeLabel.textColor = [UIColor grayColor];
[cell.contentView addSubview: UploadTimeLabel];
[UploadTimeLabel release];
UILabel *pricelabel = [[UILabel alloc] initWithFrame:CGRectMake(80, 0, 80, 30)];
pricelabel.backgroundColor = [UIColor clearColor];
pricelabel.font = [UIFont fontWithName:#"Helvetica" size:16];
pricelabel.font = [UIFont boldSystemFontOfSize:16];
pricelabel.textColor = [UIColor darkGrayColor];
pricelabel.tag = 3000;
//pricelabel.hidden = YES;
pricelabel.textAlignment = NSTextAlignmentRight;
[cell.contentView addSubview: pricelabel];
[pricelabel release];
market = [[UIButton alloc] init];;
[market setFrame:CGRectMake(200, 6, 30, 30)];
market.tag = 4000;
[market addTarget:self action:#selector(marketPressedAction:) forControlEvents:UIControlEventTouchDown];
[cell.contentView addSubview:market];
}
if( [temp count] > 0)
{
UILabel *fileNameLbl = (UILabel*)[cell.contentView viewWithTag:1000];
fileNameLbl.text =[temp objectAtIndex:indexPath.row];
UILabel *uploadlbl = (UILabel*)[cell.contentView viewWithTag:2000];
uploadlbl.text =[UploadTimeAllArr objectAtIndex:indexPath.row];
}
UIButton *marketButton = (UIButton*)[cell.contentView viewWithTag:4000];
[marketButton setTag:indexPath.row];
if([sellingArray count]>0)
{
NSLog(#"sellingArray %#",sellingArray);
if([[sellingArray objectAtIndex:indexPath.row] isEqualToString:#"0"]) // nothing
{
[marketButton setSelected:NO];
[marketButton setImage:[UIImage imageNamed:#"Marketplace.png"] forState:UIControlStateNormal];
marketButton.enabled = YES;
}
else if([[sellingArray objectAtIndex:indexPath.row] isEqualToString:#"2"]) // marketplace
{
[marketButton setSelected:YES];
[marketButton setImage:[UIImage imageNamed:#"MarketplaceSelect.png"] forState:UIControlStateNormal];
marketButton.enabled = YES;
}
}
return cell;
}

Answer 1

Your main problem here is that you are recreating new views in your cell every time this method is called. You want to create all reusable elements inside the if(cell == nil) otherwise it will make duplicates. Anything that is dynamic must be created outside of this. I took your code and modified it. This should work better.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
// Everything that does not change should go in here!
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
UILabel *pricelabel = [[UILabel alloc] initWithFrame:CGRectMake(80, 0, 80, 30)];
pricelabel.backgroundColor = [UIColor clearColor];
pricelabel.font = [UIFont fontWithName:#"Helvetica" size:16];
pricelabel.font = [UIFont boldSystemFontOfSize:16];
pricelabel.textColor = [UIColor darkGrayColor];
pricelabel.tag = 3000;
//pricelabel.hidden = YES;
pricelabel.textAlignment = NSTextAlignmentRight;
[cell addSubview:pricelabel];
UIButton *market = [UIButton buttonWithType:UIButtonTypeCustom];
[market setFrame:CGRectMake(200, 6, 30, 30)];
[market addTarget:self action:#selector(marketPressedAction:) forControlEvents:UIControlEventTouchDown];
[cell addSubview:market];
}
// find market button, since we could be reusing a cell we cannot rely on a tag
// value to find it. (This would only work with one button though).
UIButton *market;
for (UIView *subview in cell.subviews) {
if ([subview isKindOfClass:[UIButton class]]) {
market = (UIButton *)subview;
break;
}
}
// set all defaults in case of reuse
[market setImage:[UIImage imageNamed:#"DefaultImage.png"] forState:UIControlStateNormal];
market.selected = YES;
market.enabled = NO;
market.clearsContextBeforeDrawing = NO;
if([sellingArray count] > 0) {
NSLog(#"sellingArray %#",sellingArray);
if([[sellingArray objectAtIndex:indexPath.row] isEqualToString:#"0"]) {
// not sure if this is supposed to be YES or NO
market.clearsContextBeforeDrawing = YES;
[market setSelected:NO];
[market setImage:[UIImage imageNamed:#"Marketplace.png"] forState:UIControlStateNormal];
market.enabled = YES;
}
}
[market setTag:indexPath.row];
return cell;
}
Since it appears you are not using ARC, make sure you look over this code for any needed reference counting.

Answer 2

dequeReusablecellWithIdentifier: method get return the cell instance already created available,If the reference points still to nil ,we need a valid cell and create one cell to return from that cellForRowatIndexpath: method.That is what being checked in the (cell ==nil).When you create a new cell it is creation and hence all settings custom and all has to be done here.

Answer 3

Second Edit:
This was copied from an answer above:
inside the -cellForRowAtIndexPath: method:
if (!cell) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellSubtitle];
UIButton *market = [UIButton buttonWithType:UIButtonTypeCustom];
[market setFrame:CGRectMake(200, 6, 30, 30)];
[market addTarget:self action:#selector(marketPressedAction:) forControlEvents:UIControlEventTouchDown];
[cell.contentView addSubview:market];
//Add all your UILabel INITIATION stuff here as well
}
UIButton *marketButton;
for (UIView *subview in cell.subviews) {
if ([subview isKindOfClass:[UIButton class]]) {
marketButton = (UIButton *)subview;
break;
}
}
marketButton.tag = [indexPath row];
UILabel *priceLabel = [cell.contentView viewWithTag:3000];
UILabel *uploadTimeLabel = [cell.contentView viewWithTag:2000];
//Set up your labels and button now
return cell;
}
EDIT: Leaving my original answer below for posterity but I see that you are setting the table index row as the MarketButton's tag. If you're using that to figure out which dataSource object to query, this is bad practice. You should be making a custom cell which can hold a reference to the object in your data source, so you don't have to ask the button for its tag, and then ask the data source array for the object at index:tag.
The reason this is bad is because somewhere, the state of your array could change, but the table cell is still displayed and still holds a tag pointing at the wrong index. If you just have the cell keep track of the object in question, no matter what happens to the array structure you're guaranteed to be modifying the object you need to.
The only thing I would change about Firo's answer is to just add a "tag" property to each view in the cell, so you don't have to iterate each time you want to find it.
Also took out the [[UIButton alloc]init] line because it's superfluous and might be considered a dangling pointer.
if (cell == nil) {
// Everything that does not change should go in here!
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
UIButton *market = [UIButton buttonWithType:UIButtonTypeCustom];
[market setFrame:CGRectMake(200, 6, 30, 30)];
[market addTarget:self action:#selector(marketPressedAction:) forControlEvents:UIControlEventTouchDown];
market.tag = 9999;
[cell.contentView addSubview:market];
}
//don't have to do UIView iteration here
UIButton *marketButton = [cell.contentView viewWithTag:9999];