Delegation agreement, data source agreement and advanced view in view

Delegation agreement in view 、 Data source protocol and advanced view

Some advanced views have complex functions , We need to separate these complex functions from the view itself , Done by other classes . Of course , These classes need to follow the protocol specified by the view .

• Relatively simple views —— Only the entrustment agreement is specified , Include UITextField and UITextView, The corresponding naming rule of the delegation agreement is **“ View name +Delegate”**
• For some complex views , At the same time, we formulate the delegation agreement and data source agreement , These views are in iOS Not many , There are mainly selectors （UIPickerView）、 Collection view （UICollectionView） And table view （UItableView） The corresponding data source protocol naming rules are View name +DataSourse）

In the field of software , There is a classic saying ：“ Where there is input , You need to verify ”

1. Selectors

import UIKit

class ViewController: UIViewController{
    
    
    var datePicker:UIDatePicker!
    var label:UILabel!
    
    override func viewDidLoad() {
    
        super.viewDidLoad()
        let screen = UIScreen.main.bounds
        self.view.backgroundColor = .clear
        
        // Add date selector 
        let datePickerWidth:CGFloat = 320
        let datePickerHeight:CGFloat = 167
        self.datePicker = UIDatePicker(frame: CGRect(x: 0, y: 0, width: datePickerWidth, height: datePickerHeight))
        // Set simplified Chinese 
        self.datePicker.locale = NSLocale(localeIdentifier: "zh-Hans") as Locale
       // Format date and time 
        self.datePicker.datePickerMode = .dateAndTime
        self.view.addSubview(datePicker)
        
        // Add tags 
        let labelHeight:CGFloat = 200
        let labelWidth:CGFloat = 21
        let labelTopView:CGFloat = 281
        self.label = UILabel(frame: CGRect(x: (screen.size.width - labelWidth)/2, y: labelTopView, width: labelWidth, height: labelHeight))
        self.label.text = " Please select a date ："
        self.label.textAlignment = .center
        self.label.textColor = .white
        self.view.addSubview(self.label)
        
        // add to button Button 
        let button = UIButton(type: .system)
        let buttonHeight:CGFloat = 46
        let buttonWidth:CGFloat = 30
        let buttonTopView:CGFloat = 379
        button.frame = CGRect(x: (screen.size.width - buttonWidth)/2, y: buttonTopView, width: buttonWidth, height: buttonHeight)
        button.setTitle(" choice ", for: UIControl.State())
        button.addTarget(self, action: #selector(onClick(_:)), for: .touchUpInside)
        self.view.addSubview(button)
    }
    @objc func onClick(_ sender:AnyObject){
    
        let theDate:NSDate = self.datePicker.date as NSDate 
        // This property returns the selected time 
        let desc = theDate.description(with: NSLocale.current)
        // This property returns localized date information 
        NSLog("the date picked is:%@", desc)// Log information 
        let dateFormatter:DateFormatter = DateFormatter()
        dateFormatter.dateFormat = "YYYY-MM-dd HH:mm:ss"
        NSLog("the date formate is :%@", dateFormatter.string(from: theDate as Date))// Log information 
        self.label.text = dateFormatter.string(from: theDate as Date)
        
    }

}

2. Collection view

UICollecltionViewFlowLayout Is a streaming layout manager , From left to right, from top to bottom