UIViews within UIView not being drawn - ios

Question

I'm programatically creating a grid of UIViews for a tile based game. The trouble is that, in a three by three grid, only the centre tile is getting drawn at initialisation. The other tiles show up when they're tapped on - but not until (which isn't very good) - and changes to the tile at other times often don't appear. I've adapted my code from Mac OS NSViews (which works very well).
In the subclass for the 'grid' UIView (i.e. the container for the 'tile' UIViews):
- (void)renewRows:(NSInteger)rows columns:(NSInteger)columns {
for (int i=0; i<rows; i++) {
for (int j=0; j<columns; j++) {
CGRect tileRect;
tileRect.origin.x = j*tileSize.width;
tileRect.origin.y = i*tileSize.height;
tileRect.size.width = tileSize.width;
tileRect.size.height = tileSize.height;
id tileView = [[tilePrototype alloc]initWithFrame:tileRect patternNumber:arc4random_uniform(3) + 1];
//add touch recogniser. Will need additional recognisers for left and right swipe
UITapGestureRecognizer *singleFingerTap =
[[UITapGestureRecognizer alloc] initWithTarget:self
action:#selector(tapTile:)];
[tileView addGestureRecognizer:singleFingerTap];
[self addSubview:tileView];
}
}
}
Quite apart from the fact that the tiles show (and animate) correctly when they're tapped, I can see that the tiles are being created in the right place by stepping through this code in debug.
In my Tile UIView I have a drawRect as follows:
- (void)drawRect:(CGRect)dirtyRect {
NSLog(#"%f %f %f %f", dirtyRect.origin.x, dirtyRect.origin.y, dirtyRect.size.width, dirtyRect.size.height);
CGContextRef context = UIGraphicsGetCurrentContext();
_grid = (YANGrid *)[self superview];
double tileWidth = dirtyRect.size.width;
if (_flags.isRotating || _flags.iscentrenode ) {
CGRect centredSquare = CGRectMake(-(tileWidth/4), -(tileWidth/4), tileWidth/2, tileWidth/2);
[_backgroundColor set];
UIRectFill(dirtyRect);
CGContextSaveGState(context);
[self drawPatternConnections];
// Render Nodes
if (_flags.iscentrenode) {
[PatternGraphics centrenodeInRect:&centredSquare];
} else if (_flags.deviceType) {
[PatternGraphics outletnodeInRect:&centredSquare turnedOn:(_flags.isPowered && !_flags.isRotating)];
}
CGContextRestoreGState(context);
}
}
Can anyone here see if I'm missing anything - why aren't my tile UIViews being drawn correctly!