Application crashed when calling selectRowAtIndexPath - iphone

Question

In my application I have an UITableView with dynamic number of rows. Once user click on a cell, the application navigates to another UIView and user can click the back button to go to the UITableView. When going back I wanted to highlight the selected cell and scroll the cell to the center. This is how I achieve it
-(void) tableView:(UITableView *)tableView
willDisplayCell:(UITableViewCell *)cell
forRowAtIndexPath:(NSIndexPath *)indexPath {
if (!isScrollerSet && self.selectedRowNo!=-1) {
NSIndexPath *indexPath = [NSIndexPath indexPathForRow:self.selectedRowNo
inSection:0];
[self.tableViewP selectRowAtIndexPath:indexPath
animated:YES
scrollPosition:UITableViewScrollPositionMiddle];
isScrollerSet = YES;
}
}
When the user comes back this method will be call when the rows are displayed again. I set the correct row number in the didSelectRowAtIndexPath: method.
When the UITableView has less numbers of rows this works fine. Lets say UITableVIew have 100 rows and user clicked on 90th row. When he comes back application crashed when calling the didSelectRowAtIndexPath: method. Exception is as follows
*** Terminating app due to uncaught exception 'NSRangeException',
reason: '*** -[__NSArrayM objectAtIndex:]: index 3 beyond bounds
for empty array'
Then I move this code to viewDidAppear:. Now it woks with with any number of rows. I cant figure out why this happen. Can some one explain what was the reason?

Answer 1

Assuming that you do not have defective code it is possible that:
-(void) tableView:(UITableView *)tableView
willDisplayCell:(UITableViewCell *)cell
forRowAtIndexPath:(NSIndexPath *)indexPath
is called before your Datasource is initialized. For example, if your UITableView is instantiated in the UIViewController's viewDidLoad function, and then you initialize your Datasource afterwards then upon reloading the UITableView you will have a nil value.
Whereas viewDidAppear occurs later in the runtime than viewDidLoad so at that point your Datasource is valid and you're able to reference that index in the NSArray. If this is the cause of your exception then you would be able to solve it by doing your Datasource initializing at the very beginning of viewDidLoad.
This is my best guess based on the information you provided. You may want to give more detail in your question.

Answer 2

tableView willDisplayCell
method is called before your data is loaded.so deferentially it will show an error because it is not getting any index position because of no data in tableview
So the solution is that you can set an integer or any other variable and check it inside cellforRowAtindexpath. when you return back..(Better to store value in UserDafault)
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
...
if(indexpath.row==<your value>)
{
// your code.
}
....
}