iOS开发小技巧

获取Cell在tableView和当前屏幕中的位置

//获取某个cell在当前tableView上的坐标位置
CGRect rectInTableView = [tableView rectForRowAtIndexPath:indexPath];
//获取cell在当前屏幕的位置
CGRect rectInSuperview = [tableView convertRect:rectInTableView toView:[tableView superview]];

字符串UTF-8 编码与解码

// iOS9之前

// 编码
NSString *encodeStr = [@"你好世界" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

// 解码
NSString *decodeStr = [encodeStr stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

// iOS9之后

// 编码
NSString *encodeStr = [@"你好世界" stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];

// 解码
NSString *decodeStr = [encodeStr stringByRemovingPercentEncoding];

渐变色

extension UIColor {
    class func gradientLeftToRightColor(_ leftColor:UIColor,_ rightColor : UIColor,_ viewW:CGFloat) -> UIColor {
        let size = CGSize.init(width: viewW, height: 1)
        UIGraphicsBeginImageContextWithOptions(size, true, 0)
        let context = UIGraphicsGetCurrentContext()
        let colorspace = CGColorSpaceCreateDeviceRGB()
        let colors = [leftColor.cgColor,rightColor.cgColor]
        let gradient = CGGradient(colorsSpace: colorspace, colors: colors as CFArray, locations: nil)
        context!.drawLinearGradient(gradient!, start: CGPoint(x: 0, y: 0), end: CGPoint(x: size.width, y: 0), options: CGGradientDrawingOptions(rawValue: 0))
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return UIColor.init(patternImage:img!)
    }
}

计算CollectionView高度

let s = Int(SCREEN_WIDTH/collectionItemWidth)
var n = dataSource.count/s
var h: CGFloat
if n != 0 {
   if n == 1 {
       if dataSource.count > s {
           n += 1
       }
   } else {
       n = dataSource.count % s == 0 ? n : n+1
   }

   h = CGFloat(n) * collectionItemHeight + CGFloat(n-1)*collectionItemSpace + topInset + bottomInset
}
else {
   h = collectionItemHeight + topInset + bottomInset
}
collectionView.snp.remakeConstraints { (make) in
   make.top.equalTo(bottomView).offset(WH(44+10))
   make.left.right.equalTo(bottomView)
   make.height.equalTo(WH(h))
}
collectionView.reloadData()