通过UIGraphics重新设置image的大小

UIImage *icon = [UIImage imageNamed:@"图片"];
CGS
4000
ize itemSize = CGSizeMake(20, 20);//设置要显示的width跟height
UIGraphicsBeginImageContextWithOptions(itemSize, NO,0.0);
CGRect imageRect = CGRectMake(0.0, 0.0, itemSize.width, itemSize.height);
[icon drawInRect:imageRect];

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();