纯代码

自定义：

import UIKit

class CustomView: UIView {
    var lab:UILabel!
    var btn:UIButton!

    override init(frame: CGRect) {
        super.init(frame: frame)

        //初始化
        lab = UILabel()
        lab.textAlignment = .center
        lab.font = UIFont.systemFont(ofSize: 12)
        self.addSubview(lab)

        btn = UIButton()
        self.addSubview(btn)

    }

    override func layoutSubviews() {
        super.layoutSubviews()

        //设置 子控件 frame, 也可以在这里使用自动布局
        lab.frame = CGRect(x:10, y:10, width:100, height:40)

        btn.frame = CGRect(x:lab.frame.origin.x, y:lab.frame.maxY + 10, width:100, height:40)

    }

    //传入model对子控件进行配置，这里暂用NSObject
    func setUp(model:NSObject) {
        lab.text = "你好"//model.xx

        btn.setTitle("确定", for: .normal) //title:model.xx
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

使用

//纯代码 view
        let view = CustomView()
        view.frame = CGRect(x:10, y:100, width:200, height:100)
        view.backgroundColor = UIColor.cyan
        view.setUp(model: "" as NSObject)
        self.view.addSubview(view)

xib

自定义：

新建个view，再新建个同名的xib文件，在xib的 Identity insperctor （面板第三个按钮）里设置class为新建的view文件名

import UIKit

class CustomXibView: UIView {

    @IBOutlet weak var nameTF: UITextField!

    @IBOutlet weak var sexTF: UITextField!

    class func instantiateFromNib() -> CustomXibView {
        return Bundle.main.loadNibNamed("CustomXibView", owner: nil, options: nil)?.first as! CustomXibView
    }

    //用约束在xib里设置frame
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        //设置一些子视图的固定属性
        nameTF.font = UIFont.systemFont(ofSize: 12)

        sexTF.font = UIFont.systemFont(ofSize: 12)
    }

    func setUp(model:NSObject) {
        //传入model对子控件进行配置，这里暂用NSObject
        nameTF.placeholder = "请输入姓名"

        sexTF.placeholder = "请输入性别"
    }

}

使用

//xibView
        let xibView = CustomXibView.instantiateFromNib()
        xibView.frame = CGRect(x:10, y:view.frame.maxY + 10, width:200, height:100)
        self.view.addSubview(xibView)

这篇文章里有一些原理的解释： http://www.jianshu.com/p/7e47da62899c