1.swift @discardableResult 声明：

swift正常的方法如果有返回值的话,调用的时候必须有一个接收方,否则的话编译器会报一个警告,
如果在方法前加上 @discardableResult 不处理的时候就不会有警告了。也可以用一个通配符接收方法返回值,可以达到同样的目的。

2.控制器初始化：

init(urlStr: String?) {
super.init(nibName: nil, bundle: nil)
if let urlStr = urlStr {
self.urlStr = urlStr
}
}
UIView初始化：调用父类initWithFrame

3.更新View的约束：

/// 更新二级菜单约束
private func updateSecondCategoryLayout(){
if let tempHeight = height {
secondCategoryView.needsUpdateConstraints()
tempHeight.update(offset: )
UIView.animate(withDuration: 0.25) {
self.secondCategoryView.layoutIfNeeded()
}
}
}

4.上拉加载更多：

printTable.mj_footer = MJRefreshAutoNormalFooter(refreshingBlock: { [weak self] in
guard let `self` = self else {return}
if self.pageNum <= self.totalPage {
self.loadData()
} else {
self.printTable.mj_footer.endRefreshing()
self.printTable.mj_footer.endRefreshingWithNoMoreData()
}
})

5.UIView.performWithoutAnimation：

UIView.performWithoutAnimation {
planDiscountCollectionView.reloadSections(IndexSet(integer: IndexSet.Element()))
}

//视图转换时不执行动画，参数为block对象，来执行你要执行的代码

• (void)performWithoutAnimation:(void (^)(void))actionsWithoutAnimation

6.十进制转换：

if tempTextCount.decimalValue > NSDecimalNumber(string: WaiterManager.shared.waiterPower(PowerCode.ignore)?.powerValue).decimalValue {
}

7.限制textField只能输入3个字符：

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    let currentCharacterCount = textField.text?.count ??  
    let newLength = currentCharacterCount + string.count - range.length  
    return newLength <=  
}

8.变量安全使用使用set方法private，可以调方法改变值：

class HHTComboGlobalData: NSObject {
static let shared = HHTComboGlobalData()

private(set) var comboModes:\[ComboModel\] = \[\]

func setComboModel(with dicts:\[JSONDictionary\]) {  
    comboModes.removeAll()  
    comboModes = dicts.flatMap { (dict) -> ComboModel? in  
        return ComboModel(with: dict)  
    }  
}  

}

9.for循环创建九宫格：

private func setupUI() {
let count: Int =
let width: CGFloat =
let height: CGFloat =
let bgViewWidth: CGFloat =
let col: Int =
// 间距
let hMargin = (bgViewWidth - (CGFloat(col) * width)) / CGFloat((col+))
let vMargin:CGFloat =

    var row:Int =  
    for i in ..<count {  
        let button: UIButton = UIButton()  
        button.setTitle("打印一", for: .normal)  
        button.setTitleColor(UIColor.white, for: .normal)  
        button.backgroundColor = UIColor.red  
        if i%col ==  {  
            row +=  
        }  
        var y: CGFloat =  
        if row ==  {  
            y =  
        } else {  
            y = vMargin + (height + vMargin) \* CGFloat(row)  
        }  
        let x:CGFloat = hMargin + (width + hMargin) \* CGFloat(i%col)  
        button.frame = CGRect(x: x, y: y, width: width, height: height)  
        bgView.addSubview(button)  
        bottomMargin = button.frame.maxY +  
    }  
    bgHeightConstraint.constant = bottomMargin!  
}  

}