Question

Can I call tableViewcellForRowAtIndexPathtableView in heightForRowAtIndexPath to find cell’s size?

Is it too expensive in terms of performance, if not how else can I find cells height if it comes from XIB?

Answer 1

Don’t do this. It won’t work anyway. tableView:heightForRowAtIndexPath: is called for all of your cells. And cellForRowAtIndexPath: won’t return cells for the non visible indexPaths anyway.

When tableView:heightForRowAtIndexPath: is called the first time (just after numberOfSectionsInTableView: and tableView:numberOfRowsInSection:) there is no cell at all.

Just check the height of the cell in interface builder. Select the UITableViewCell view and look into the size panel.

Because tableView:heightForRowAtIndexPath: is called for every cell you should set the height of the cells in viewDidLoad if you only have one height. If tableView:heightForRowAtIndexPath: is not implemented it is not called, which is great if you have many cells.

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tableView.rowHeight = 44.0f;
}

If you have different heights, figure out the height from your dataSource. E.g. check the object at the indexPath from your dataSource NSArray and use the same logic you use in tableView:cellForRowAtIndexPath: to figure out which cell to use. Then return the appropriate height.

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EDIT: I just tested it and querying the tableView for a cell in tableView:heightForRowAtIndexPath: causes an infinite loop.