I am trying to understand how the rendering of each cell works. Here's my code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"QuestionCell";
static NSString *cellNib = #"QuestionsTableViewCell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell == nil)
{
//cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:cellNib owner:self options:nil];
cell = [nib objectAtIndex:0];
NSLog(#"%#", #"--> load from nib");
}
return cell;
}
The NSLog in this code is called 8 times initially (because I have 8 rows visible initially). Then when I start scrolling, it's called once and then no more after. I thought it should've been called once and that's it since it should be re-using it after the first call? And why is it called once more after the initial 8? (scratching head...)
It's possible that there could be 9 cells on screen when you are scrolling the table view. This wasn't needed when you started but as you scroll, the 9th cell is required as the top one leaves, a new cell at bottom enters. A cell can't be reused in halves. :)
Related
I'm trying to implement "Load more..." on a tableView. I've done it, but I don't know if it's efficient.
The thing is that I have custom cells, and if I do like this:
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"Cell";
ArticlesCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell==nil)
{
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"ArticlesCell" owner:self options:NULL];
cell = (ArticlesCell *) [nib objectAtIndex:0];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
}
tableView.backgroundColor = cell.backgroundColor;
if (indexPath.row <= (self.bookmarks.count - 1)) {
[self configureCell:cell atIndexPath:indexPath];
}else{
cell.textLabel.text = #"Load more...";
}
return cell;
}
It works great but what happens is it's reusing the cells, and if I scroll, every fifth cell (this is height 77.0) will have the label "Load more...", but actually do it's job as normal.
I found this workaround, but I don't know is it good and efficient.
Here it is:
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"Cell";
if (indexPath.row <= (self.bookmarks.count - 1)) {
ArticlesCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell==nil)
{
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"ArticlesCell" owner:self options:NULL];
cell = (ArticlesCell *) [nib objectAtIndex:0];
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
}
tableView.backgroundColor = cell.backgroundColor;
[self configureCell:cell atIndexPath:indexPath];
return cell;
}else{
UITableViewCell *cell = [[UITableViewCell alloc] init];
cell.textLabel.text = #"Load more...";
return cell;
}
}
As you can see I'm making the "Load more..." cell a simple UITableViewCell, and not reusing it, since it's only one. Is this good approach? Can you advice me in something better?
Thank you!
Another approach would be to use 2 different cell identifiers, one to identify and reuse (once initially created) an ArticlesCell and another to identify and reuse (once initially created) a "Load more..." UITableViewCell. At least then you will only create the "Load more..." UITableViewCell once rather than every time it scrolls into view.
static NSString *ArticleCellIdentifier = #"ArticleCell";
static NSString *LoadMoreCellIdentifier = #"LoadMoreCell";
The LazyTableImages Apple iOS sample project uses a similar approach (see the Classes/ RootViewController.m).
When you are click on loadmore button then increase the number of rows and reload the tableview . i.e in the method numberofrowsinsection.Let me know if you need any more
I have configured a table view cell, whose tables cell is loaded from another xib, both the filename and the identities are called,BlogViewControllerTableCell
Most of them works properly, but some contents in the cells keep changing while scrolling.
No matter I use the array value, or simply put the [indexpath row].
The below is the code,
I would be appreciate for your help.
Thanks.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"BlogViewControllerTableCell"];
if (cell == nil) {
// Load the top-level objects from the custom cell XIB.
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:#"BlogViewControllerTableCell" owner:self options:nil];
// Grab a pointer to the first object (presumably the custom cell, as that's all the XIB should contain).
cell = [topLevelObjects objectAtIndex:0];
}
student_name.text = [NSString stringWithFormat:#"%#", [[student_list objectAtIndex:[indexPath row]] objectForKey:#"name"]];
return cell;
}
I am having trouble wiht UITableViewCell loaded from nib. I used apple documentation to that but I do't know where I am going wrong. UITableViewCell created through IB contains 5 UIlable. Nib are loaded perfectly but the problem is when I scroll text of the label changes automatically to different.
Following is the my code for cell for row at indexpath. Please let me know where I am going worng.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
int rowNo = [indexPath row];
NSLog(#"Row No:%d",rowNo);
Transfer *tempTransferRecord =(Transfer*)[self.transferInformation objectAtIndex:rowNo];
seasonYear.text=tempTransferRecord.seasonYear;
longName.text=tempTransferRecord.longName;
transactionDate.text=tempTransferRecord.transactionDate;
toTeam.text=tempTransferRecord.toTeam;
fromTeam.text=tempTransferRecord.fromTeam;
/*
static NSString *MyIdentifier = #"MyIdentifier2";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier] ;
if (cell == nil)
{
[[NSBundle mainBundle] loadNibNamed:#"PlayerTransfers" owner:self options:nil];
cell=transfersInfoCell;
self.transfersInfoCell=nil;
}
*/
static NSString *CellIdentifier = #"MyIdentifier2";
static NSString *CellNib = #"PlayerTransfers";
UITableViewCell *cell = (UITableViewCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:CellNib owner:self options:nil];
cell = (UITableViewCell *)[nib objectAtIndex:0];
}
// perform additional custom work...
return cell;
}
Try moving your cell loading code to the top of cellForRowAtIndexPath, and the rowNo and value setting after that. Cells changing content must mean you're either changing what's in the data source between when you first set it and when you scroll, or you're setting values at the wrong point in time (i.e setting values on row 5 but then loading row 6 from a nib, or setting values on a row but then loading the nib for it afterwards so the values you set are overridden). Also, I'm a bit concerned that you set local variables rather than, say, (PlayerTransfers*)cell.seasonYear.text = tempTransferRecord.seasonYear or (UILabel *)[cell viewWithTag:1].text = tempTransferRecord.seasonYear. Shouldn't you be setting the values within each cell rather than on your table view class? That could explain why values are changing to something different: you may use the same variables to set every cell.
Have you set a CellIdentifier in Interface Builder?
I feel like a real noob asking this, but here's my problem:
I want to show a tableView, with 7 custom cells. None of these cells is reused. That means the user will see 7 different cells, not more, not less.
I created the cells in the viewDidLoad method, and added all those cells in the listCells-array. After that, I used easy-mode to draw those cells:
UITableViewCell *cell = nil;
if (indexPath.row == 0)
{
static NSString *MyIdentifier = #"Cell";
cell = (DetAlertCell *)[localTableView dequeueReusableCellWithIdentifier:nil];
if (cell == nil) {
[[NSBundle mainBundle] loadNibNamed:#"DetAlertCell" owner:self options:nil];
cell = [listCells objectAtIndex:indexPath.row];
}
}
....
However, this won't work. It shows me a blank view. Every cell is created using a .xib-file and a .h and .m class. Is there anything that I'm missing and should do?
Just don't call the [localTableView dequeueReusableCellWithIdentifier:nil] and loa the correct cell for the index path.
Also you say that you load the cells in the viewDidLoad, then why do you load the nib:
[[NSBundle mainBundle] loadNibNamed:#"DetAlertCell" owner:self options:nil];
They should already be the array should they not.
And why to you check if the row is 0 then load the row, still will only load the first row.
Try this:
- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
return [listCells objectAtIndex:indexPath.row];
}
I have a class which extends UITableViewCell. For the purpose of this exercise, let's call it "CustomCell". In CustomCell, I have a UIImageView IBOutlet setup. The image instance name in this case is myImage. I wish to display this image based on certain criteria that's coming back from a server. That data is a dictionary which in this exercise we'll call "serverData". At first, the UITableView renders just fine with the UIImageView showing up in cells which it should. The problem occurs when I start scrolling the actual UITableView, the image gets lost. Somehow it's not properly being either cached or dequeued. Not sure where the problem is or how to better improve on this code. Here's an excerpt:
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CustomCellIdentifier = #"CustomCellIdentifier";
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:CustomCellIdentifier];
if (cell == nil) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"CustomCell"
owner:self options:nil];
cell = (CustomCell *)[nib objectAtIndex:0];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
}
NSDictionary *serverData = myData // previously defined.
if ([[serverData valueForKey:#"foo"] isEqualToString:#"0"])
cell.myImage.hidden = YES;
cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton;
return cell;
}
For memory reasons UITableView reuses cells when scrolling (e.g the dequeueReusableCellWithIdentifier) call.
What this means is that the cell you receive could have been configured in anyway that is valid for use with that identifier so you must reset all these properties.
In your case I suspect you are being given a cell with an image that had been hidden so this will fix it:
NSDictionary *serverData = myData // previously defined.
if ([[serverData valueForKey:#"foo"] isEqualToString:#"0"])
cell.myImage.hidden = YES;
else
cell.myImage.hidden = NO;
Remember that your cells are being reused, so you need to reset the cell.myImage.hidden value each time you use that cell
if (cell == nil) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"CustomCell"
owner:self options:nil];
cell = (CustomCell *)[nib objectAtIndex:0];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
} else {
cell.myImage.hidden = NO;
}