Case
Normally you would use the cellForRowAtIndexPath delegate method to setup your cell. The information set for the cell is important for how the cell is drawn and what the size will be.
Unfortunatly the heightForRowAtIndexPath delegate method is called before the cellForRowAtIndexPath delegate method so we can't simply tell the delegate to return the height of the cell, since this will be zero at that time.
So we need to calculate the size before the cell is drawn in the table. Luckily there is a method that does just that, sizeWithFont, which belongs to the NSString class. However there is problem, in order to calculate the correct size dynamically it needs to know how the elements in the cell will be presented. I will make this clear in an example:
Imagine a UITableViewCell, which contains a label named textLabel. Within the cellForRowAtIndexPath delegate method we place textLabel.numberOfLines = 0, which basically tells the label it can have as many lines as it needs to present the text for a specific width. The problem occurs if we give textLabel a text larger then the width originally given to textLabel. The second line will appear, but the height of the cell will not be automatically adjusted and so we get a messed up looking table view.
As said earlier, we can use sizeWithFont to calculate the height, but it needs to know which Font is used, for what width, etc. If, for simplicity reasons, we just care about the width, we could hardcode that the width would be around 320.0 (not taking padding in consideration). But what would happen if we used UITableViewStyleGrouped instead of plain the width would then be around 300.0 and the cell would again be messed up. Or what happends if we swap from portrait to landscape, we have much more space, yet it won't be used since we hardcoded 300.0.
This