Wrong value from UITableView:rowHeight at iOS8

Question

The code I used to create a rectangle (at least until iOS7) was

CGRect rect = [cTableView frame];
rect.origin.y += [cTableView rowHeight];
searchOverlayView = [[BecomeFirstResponderControl alloc] initWithFrame:rect];

On iOS7, cTableView (an instance of a UITableView) returned 44. Testing in iOS8 with an iPhone 5s returns -1.

Why is this happening? What is the correct code that needs to be used in order for my app to be backwards compatible with iOS7?

Answer 1

Apple changed the default row height in iOS8 to UITableViewAutomaticDimension, which is declared as -1. This means that your table view is set up for automatic cell height calculation.

You will either need to implement autoLayout (recommended) or implement the new delegate method: heightForRowAtIndexPath. Here's a great question about auto layout: Using Auto Layout in UITableView for dynamic cell layouts & variable row heights

Seems like you were effectively hard coding 44 (the old default) anyway, though, so you could just do that (not recommended).

Answer 2

This made me struggle for hours. I ended up hard coding the value to 44:

self.tableView.rowHeight = 44;

Answer 3

There is a performance penalty for implementing heightForRowAtIndexPath that I prefer not to incur when all rows in a table are the same height and never change at runtime (it is called once for every row, each time the table is displayed).

In this situation, I continue to set "Row Height" in the XIB and use the following iOS 8 friendly code when I need rowHeight (it works on iOS 7 and below too).

NSInteger aRowHeight = self.tableView.rowHeight;
if (-1 == aRowHeight)
{
    aRowHeight = 44;
}

This allows you to keep freely editing Row Height in the XIB and will work even if Apple fixes this bug/feature in the future and a XIB set Row Height = 44 stops coming back as -1.

Answer 4

If you accidentally change the row height in IB from 44 to something else (like 40), automatic cell size calculation fails. You owe me 3 hours, Apple.

Answer 5

One more consideration is that if you are calculating the height based on existing view dimensions, the heightForRowAtIndexPath method may be called before viewDidLayoutSubviews.

In this case, override viewDidLayoutSubviews, and recalculate the frame.size.height value for all the visible cells.

Answer 6

My solution to this problem:

@interface MCDummyTableView () <UITableViewDataSource, UITableViewDelegate>
@end

@implementation MCDummyTableView

    - (instancetype) initWithFrame:(CGRect)frame style:(UITableViewStyle)style {
        frame = (CGRect){ 0, 0, 100, 100 };

        self = [super initWithFrame:frame style:style];
        if(!self) return self;

        self.dataSource = self;
        self.delegate = self;

        [self registerClass:[UITableViewCell class] forCellReuseIdentifier:@"CELL"];

        return self;
    }

    - (NSInteger) numberOfSections {
        return 1;
    }

    - (NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
        return 1;
    }

    - (UITableViewCell*) cellForRowAtIndexPath:(NSIndexPath*)indexPath {
        /*
            UITableView doesn't want to generate cells until it's in the view hiearchy, this fixes that.
            However, if this breaks (or you don't like it) you can always add your UITableView to a UIWindow, then destroy it
            (that is likely the safer solution).
        */

        return [self.dataSource tableView:self cellForRowAtIndexPath:indexPath];
    }

    - (UITableViewCell*) tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath {
        return [self dequeueReusableCellWithIdentifier:@"CELL"];
    }

    - (CGFloat) defaultRowHeight {
        return [self cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]].frame.size.height;
    }

@end

I really don't like hardcoding things. I use this class to cache the default cell height early on in the app.