创建Swift闭包以创建UIView

Question

我想将DRY快速应用于正在创建的行。如何重构此代码，以便调用闭包？它位于视图控制器上。

var topLineView: UIView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}()

var bottomLineView: UIView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}()

var centerLineView: UIView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}()

我尝试创建变量，但是导致错误：

let lineView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}

var centerLineView = lineView()

错误（无法推断闭包类型，等等。]

Answer 1

Swift无法推断闭包的返回类型，因此您需要提前告知它要返回UIView。这样可以编译并正常运行。

let lineView = { () -> UIView in
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}
var myViewFromClosure = lineView()
var myViewFromClosure2 = lineView()
var myViewFromClosure3 = lineView()

但是，在这种情况下，我个人会选择function而不是closure。像这样：

func lineViewFunc() -> UIView {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}

var myViewFromFunc = lineViewFunc()
var myViewFromFunc2 = lineViewFunc()
var myViewFromFunc3 = lineViewFunc()

Answer 2

只需提供足够的值即可正确推断类型。

任一：

let lineView: () -> UIView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}

var centerLineView = lineView()

或

let lineView: UIView = {
    let lineView = UIView()
    lineView.layer.borderWidth = 1.0
    lineView.layer.borderColor = UIColor.lightGray.cgColor
    return lineView
}()

var centerLineView = lineView