Blurry UILabel as programmatic subview of UITableV

Question

I am adding a UILabel instance as a subview of my custom UITableViewCell instance's contentView.

When I select the cell, the row is highlighted blue, except for the background of the label. The label text is sharp.

When I set the label and content view backgroundColor property to [UIColor clearColor], the label text becomes blurry.

How do I set the label background color to be clear, to allow the row highlight to come through, while still keeping the label text sharp?

One suggestion I read elsewhere was to round the label's frame values, but this did not have any effect.

CODE

Here is a snippet of my custom UITableViewCell subview's -setNeedsLayout method:

UILabel *_objectTitleLabel = [[UILabel alloc] initWithFrame:CGRectNull];
_objectTitleLabel.text = [self.awsObject cleanedKey];
_objectTitleLabel.font = [UIAppDelegate defaultObjectLabelFont];
_objectTitleLabel.highlightedTextColor = [UIColor clearColor]; //[UIAppDelegate defaultLabelShadowTint];
_objectTitleLabel.backgroundColor = [UIColor clearColor]; //[UIAppDelegate defaultWidgetBackgroundTint];
_objectTitleLabel.frame = CGRectMake(
        kCellImageViewWidth + 2.0 * self.indentationWidth,
        0.5 * (self.tableView.rowHeight - 1.5 * kCellLabelHeight) + kCellTitleYPositionNudge,
        contentViewWidth,
        kCellLabelHeight
);
_objectTitleLabel.frame = CGRectIntegral(_objectTitleLabel.frame);
_objectTitleLabel.tag = kObjectTableViewCellTitleSubviewType;
//NSLog(@"_objectTitleLabel: %@", NSStringFromCGRect(_objectTitleLabel.frame));
[self.contentView addSubview:_objectTitleLabel];
[_objectTitleLabel release], _objectTitleLabel = nil;

...

self.contentView.backgroundColor = [UIAppDelegate defaultWidgetBackgroundTint]; 
self.contentView.clearsContextBeforeDrawing = YES;
self.contentView.autoresizesSubviews = YES;
self.contentView.clipsToBounds = YES;
self.contentView.contentMode = UIViewContentModeRedraw;

Answer 1

Use round(); C functions are provided for a reason.

#define roundCGRectValues (frame) \
frame = CGRectMake(round(frame.origin.x),round(frame.origin.y),round(frame.size.width),round(frame.size.height));

All you need.

Answer 2

The issue is sub-pixel rendering, which occurs when your origin (which is a float value) has a non-zero fractional component. Round to the nearest whole number and you should be fine.

Answer 3

Does -setNeedsLayout get called even for dequeued reusable cells? If so, the cell will already have the label added to the content view, and you will draw it twice, making it blurry. You can inefficiently solve this by removing all of the content view's subviews before you add your subview:

for (UIView *subview in [[self contentView] subviews]) {
     [subview removeFromSuperview];
}

A better solution would be to provide properties on your cell subclass to let you modify the content of a reused cell as-needed, rather than rebuilding its view hierarchy from scratch.

Answer 4

I ran into this problem myself today, and read somewhere that non-integer values for the origin and size of the UILabel's frame can cause this (I know they're floats, but you know what I mean). There has got to be a more elegant solution, but this quick hack appears to have solved the problem for me:

self.valueLabel.frame = CGRectMake((int) frame.origin.x, (int) frame.origin.y, (int) frame.size.width, (int) frame.size.height);

If you find a better solution, please let me know, I'd love to replace this hack with something a bit more tasteful.

Answer 5

Another cause of garbled/blurry text is cell reuse. If you are de-queuing a reusable cell then it may redraw with different dimensions somewhere else and again be re-used when it gets to your cell with the garbled text.

To ensure the cells are unique be sure to allocate a new cell for the indicies where the text is garbled, and mark that UITableViewCell instance with a different reuse identifier. This is only practical of course if you're dealing with a very small number of cells and if you know exactly which cells are causing problems.

Answer 6

Setting shouldRasterize to YES may introduce blurriness. Set the rasterization scale and that should eliminate the blurriness. [self.layer setRasterizationScale:[[UIScreen mainScreen] scale]];