Delegate

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1. 前言

以前只知道怎么用 Delegate，能够传值和回传值。最近写代码封装一个 UIPickerView+UIButton，时候需要传值，就想到了 Delegate。但是自己写一个却把我难住了。最后看了还是看了一个 Demo, 单步调试才算真正理解的Delegate 整个流程和原理。

简单来说就是声明 Protocol，添加触发 调用Protocol 方法的条件，被委托者设置 Delegate = self，就会在触发条件下调用 Protocol 方法（参数和返回值可实现双向传值）。

主要看了这个教程：
CREATE CUSTOM DELEGATE AND PROTOCOL IOS | SWIFT & OBJECTIVE-C，下面是作者提供的源码Objective-C  Project，Swift Project。

教材中MyTimer是Custom ViewController，我实际工作中是 UIView，也是参考了另外一篇 Apple 的教程：Implement a Custom Control。发现开发真的离不开 Google，但是前提是要有思路，或者对一个项目或者难题，要有整体的框架和可用的知识点熟悉。

2. 源码

下面是UIPickerView+UIButton封装后的源码：

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//  GenderPickerView.swift

import UIKit

protocol GenderPickerViewDelegate: NSObjectProtocol {
    func genderPickerDidSelectItem(row: Int)
}

class GenderPickerView: UIView, UIPickerViewDataSource, UIPickerViewDelegate {
    var delegate: GenderPickerViewDelegate!
    var toolbar: UIToolbar!
    var picker: UIPickerView!
    var genderPickerViewData = ["不告诉你", "男", "女"]
    var genderSelectedRow = 0

    override init(frame: CGRect) {
        super.init(frame: frame)
        toolbar = UIToolbar.init(frame: CGRectMake(0, 0, UIScreen.mainScreen().bounds.width, 20))
        toolbar.barStyle = .Default
        toolbar.sizeToFit()

        let cancelButton = UIBarButtonItem.init(title: "取消", style: UIBarButtonItemStyle.Done,  target: self, action: "genderPickerDidCancel")
        let flexibleButton = UIBarButtonItem.init(barButtonSystemItem: UIBarButtonSystemItem.FlexibleSpace, target: self, action: nil)
        let doneButton = UIBarButtonItem.init(title: "确定", style: UIBarButtonItemStyle.Done,  target: self, action: "genderPickerDidSelect")
        toolbar.setItems([cancelButton, flexibleButton, doneButton], animated: true)

        picker = UIPickerView.init(frame: CGRectMake(0, 44, UIScreen.mainScreen().bounds.width, 120))
        picker.dataSource = self
        picker.delegate = self

        addSubview(toolbar)
        addSubview(picker)
    }

    convenience init() {
        self.init(frame: CGRectMake(0, UIScreen.mainScreen().bounds.height - 164, UIScreen.mainScreen().bounds.width, 164))
    }

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


    //MARK: - 性别选择视图
    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return 3
    }

    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return genderPickerViewData[row]
    }

    func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        genderSelectedRow = row
    }

    func genderPickerDidSelect() {
        delegate?.genderPickerDidSelectItem(genderSelectedRow)
        removeFromSuperview()
    }

    func genderPickerDidCancel() {
        removeFromSuperview()
    }
}
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//  PersonalInfoViewController.swift

import UIKit

class ViewController: UIViewController, GenderPickerViewDelegate {
    var genderPicker: GenderPickerView!
    override func viewDidLoad() {
        super.viewDidLoad()
        genderPicker = GenderPickerView.init()
        genderPicker.delegate = self
        self.view.addSubview(genderPicker)}

    //MARK: - GenderPickerViewDelegate
    func genderPickerDidSelectItem(row: Int) {
        // Do something
    }
}