UITableView comes to a crawl when adding a UILabel with cornerRadius to each cell

问题

I'm adding a UILabel to each cell in my table view. This presents no problem initially. When I round the corners of the UILabel using layer.cornerRadius scrolling the table view grinds to a halt.

 UILabel *label1 = [[UILabel alloc] initWithFrame:CGRectMake(cell.bounds.origin.x+10 ,5, 30, 30)];
 label1.backgroundColor = ([[managedObject valueForKey:@"color"] hasPrefix:@"FFFFFF"]) ? [UIColor blackColor] : color;
 label1.layer.cornerRadius = 10.0f;
 [cell addSubview:label1];

回答1:

I've tried this before myself and found that it's useless for any kind of view that moves. You should create an image with rounded corners and add that as the background of your label instead.

回答2:

There is no need for an image with rouned corners - see the answer by fknrdcls to this question:

UILabel layer cornerRadius negatively impacting performance

Basically, you simply need to give your label a transparent background, and add the backgroundcolor to the layer instead. Then, you can disable maskToBounds, which greatly improves performance. So your code becomes:

UILabel *label1 = [[UILabel alloc] initWithFrame:CGRectMake(cell.bounds.origin.x+10 ,5, 30, 30)];
label1.backgroundColor = [UIColor clearColor];
label1.layer.backgroundColor=[UIColor whiteColor].CGColor;
label1.layer.cornerRadius = 10.0f;
label1.layer.masksToBounds = NO;
label1.layer.shouldRasterize = YES;

回答3:

for an UIImageView the UILabel trick didn't work because I had to crop an image as well, not just a background color. the quickest solution I found was to rasterize the view's parent whenever I animated it (I have a sliding panel).

来源：https://stackoverflow.com/questions/2256314/uitableview-comes-to-a-crawl-when-adding-a-uilabel-with-cornerradius-to-each-cel