Expand section UITableview getting crash when reloadSections - iphone

Question

Trying to expand the sections each section will have two rows when expanded. It is giving crash. Below is code am trying.
-(NSInteger) numberOfSectionsInTableView:(UITableView *)tableView
{
return [self.mArrQues count];
}
-(NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if(!helpOn)
return 1;
else
if(section == selectedCellIndexPath)
{
return 2;
}
else{
return 1;
}
return 1;
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"CellIdentifier";
UITableViewCell *cell;
cell = [self.mHelpTable dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
}
else{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
}
UIView* myBackgroundView = [[UIView alloc] initWithFrame:CGRectZero];
myBackgroundView.backgroundColor = [UIColor colorWithRed:240.0/255.0 green:240.0/255.0 blue:240.0/255.0 alpha:1.0];
cell.backgroundView = myBackgroundView;
//[cell addSubview:myBackgroundView];
if(!helpOn)
{
cell.textLabel.text = [self.mArrQues objectAtIndex:indexPath.section];
}
else
{
if(indexPath.row == 0)
{
cell.textLabel.text = [self.mArrQues objectAtIndex:indexPath.section];
}
else{
cell.textLabel.text = [self.mArrAns objectAtIndex:indexPath.section];
}
}
cell.selectionStyle = UITableViewCellSelectionStyleNone;
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
return cell;
}
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
helpOn = !helpOn;
int ind = indexPath.section;
if(ind == selectedCellIndexPath)
{
}
else{
helpOn = 1;
}
if(helpOn)
{
selectedCellIndexPath = indexPath.section;
[self.mHelpTable reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationFade];
}
else
{
if(indexPath.row == 0)
{
//selectedCellIndexPath = indexPath.section;
[self.mHelpTable reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationFade];
}
}
}
Error :
Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (2) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'

Answer 1

As you are changing the number of cells at section, you need to wrap the reload operation with beginUpdates and endUpdates as well as specify the cells insertion and removal with insertRowsAtIndexPaths:withRowAnimation and deleteRowsAtIndexPaths:withRowAnimation:.
Alternatively you can use 'reloadData` to reload all the cells, however there will be problems either with animation or user experience if you use it.

Answer 2

Remove this from your code.
else{
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
}
There is no need to alloc your cell if it is nil, tableview will reuse from previous cell in this line
cell = [self.mHelpTable dequeueReusableCellWithIdentifier:cellIdentifier];
AND
Make in .h
int selectedCellIndexPath;
BOOL selected;
in .m
-(NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
if (section==selectedCellIndexPath)
{
//selected > this is because initialy selectedCellIndexPath is 0 and section is also 0
if (selected) {
return 2;
}
else{
return 1;
}
}
else{
return 1;
}
return 1;
}
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"CellIdentifier";
UITableViewCell *cell;
cell = [self.mHelpTable dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];
}
UIView* myBackgroundView = [[UIView alloc] initWithFrame:CGRectZero];
myBackgroundView.backgroundColor = [UIColor colorWithRed:240.0/255.0 green:240.0/255.0 blue:240.0/255.0 alpha:1.0];
cell.backgroundView = myBackgroundView;
//[cell addSubview:myBackgroundView];
//if(!helpOn)
if (indexPath.section!=selectedCellIndexPath)
{
cell.textLabel.text = [mArrQues objectAtIndex:indexPath.section];
}
else
{
if(indexPath.row == 0)
{
cell.textLabel.text = [mArrQues objectAtIndex:indexPath.section];
}
else{
cell.textLabel.text = [mArrAns objectAtIndex:indexPath.section];
}
}
//cell.textLabel.text = [self.mArrQues objectAtIndex:indexPath.section];
cell.selectionStyle = UITableViewCellSelectionStyleNone;
cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
return cell;
}
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
selected= !selected;
selectedCellIndexPath = indexPath.section;
//selectedCellIndexPath = indexPath.row;
[self.mHelpTable reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationFade];
}