Swift.md

Swift

• var indexL: Int = 0
  -Claim a variable with Int;

• indexL = Int.random(in:1...6)
  -Generate a random Int from 1 to 6 by "...";

• print(indexL)
  -When running the project, check whether the action did as the code shows in console by print;

• var str = "hello"
  -If the variable can be clearly recognised after "=", it don't need to claim the variable as the first line shows;
  -It is the same as var indexL = 0;

• command delete
  -When move the mouse on the last of current line, it can delete the whole line;

• command shift enter
  -When open a background not create a project on Xcode, it can run the pure code without UIview or simulator;

• command option [
  -Move the whole line codes up;
  -] means move the whole line codes down;

• let name = "grace"
  -It is same as final string;
  -The value of which let claims cannot be changed;
  -It cannot assign to value that 'name' is constant;
  -It needs less and less and less storage than ordinary variables;
  -We can claim the variable as let at the beginning, if we need to change its value, change it after then;

• let fullName = "\(name) liu"
  -"name" is another varible with let which contains the value of "grace";

• let flag: Bool = false
  -Bool not boolean;

• let mini = 3.14
  -It will be double, because it will directly recognise it as double;
  -But if we do not know the details of this variable, we should claim double though;

• diceImageViewL.image = UIImage(named = "dice-\(indexL)"
  -Change diceimageViewL's imageView into dice-X;

• let diceArray = ["dice-1", "dice-2", "dice-3", "dice-4", "dice-5", "dice-6"]
  -An array with String;
  -diceImageViewL.image = UIImage(named = diceArray[indexL];

• **func methodName() {}
  -Claim a function;

• Tells the receiver that a motion event has ended.

     override func motionEnded(_ motion: UIEvent.EventSubtype, with event: UIEvent?) {
              code
     }

  -motion: An event-subtype constant indicating the kind of motion. A common motion is shaking, which is indicated by UIEvent.EventSubtype.motionShake;
  -event: An object representing the event associated with the motion;

• Hard Code -E.g. print(1x) can only print 1x, cannot print 2x, so it is hard code;
  -If we want to print 2x/3x, etc. Use the parameter in the method();

• function

     func getMilk (nums: Int, total: Int) {
          total = nums * 5
          print(\(nums))
          print("Buy \(nums) bottles of milk needs \(total) pounds.")
     }  

  -Think more than twice about the license of the parameters -> nums: Int;
  -let rest = getMilk(nums: 2, total: 100);

• The type for return variable is **->Int**

     func getMilk (nums: Int) -> Int {
          return 0
     }

• if-else

     func textSimilar (herName: String, hisName: String, num: Int) -> String {
          if nums > 80 {  
             return "Up"   
          }else if nums > 40 && nums <=80{  
             return "Mid"
          }else{  
             return "Down"
          }   

• round(double)
  -Focus on a double variable value into 4cut5add BUT will return a double as well like 22 .0;

• pow(2, 3)
  -2^3 = 2x2x2;

• loop

     let nums = [1,2,7,4,3]`  
     for num in nums {
         print(num)
     }

  -It will print 1,2,7,4,3 is the same as for the below in java

     for(int item:arrayName){
         System.out.println(item);
     } 

  -The basic principle is:

     var num = nums[0]
     print(\(num))
     num = nums[1]
     print (\(num))
     then ...

• The original loop

     for num in 1...10{  
         print(num)
     }

  -It will print 1,2,3,...,10 as what java shows:

     for(int i=1; i<=10; i++) {
         System.out.println(i);
     }

• Fixed scope
  -1..<10: 10 is open, so the range is 1-9;
  -1>..10: 1 is open, so the range is 2-10;

• Add condition on loop

     for i in 1...10 where i % 2 == 0 {
           print(i)
           print("The current number is \(i)")
     }

  -It will print 2,4,6,8,10 which is same as what java show:

     for(int i=1; i<=10; i++) {
         if(i % 2 == 0) {
                System.out.println(i);    
         }
     }

• (1...10).reversed()
  -Change 1->10 into 10->1;

• How to use methods

     func calSong (howmany total: Int) {
     }
     
     calSong(howmany: 10)

  -howmany: It is the name to use;
  -total: It is the name to run in the code;
  -Target: To guarantee the frequency of different meaning of function target, which is focus on foreigner? Anyway, don't mention it;
  -If we don't care foreigner language:

     func calSong (_ total: Int) {
     }
     
     calSong(10)   

• IBAction of UIButton

     @IBAction func touchKeys (_ sender: UIBotton) {
     }

  -_: The meaning of null parameter outside method which we have mentioned before. It is the parameter name which when we use this method and give a name of this parameter;
  -sender: It is the sender of this action, the same as the object which sends this command. It is equal to what shows as follows that sender is btn:

     @IBOutlet weak var btn: UIButton    
     @IBAction func touchKeys (_ sender: btn) {    
     }    

• if send.tag == 1 {}

• import Foundation
  -It is everything we can use in the .swift, which after we created a .swift file it will appear;

• import UIKit
  -It is a more wide package than Foundation, it contains Foundation;

• Initialise a class

  init(text: String, ans: Bool) {
       quesText = text
       quesAns = ans
  }    

• Judge then give a value
  -var name = (flag ? "yes" : "no");

• nil
  -It is the same as null in java/c/etc.;

• Transfer variable type
  -Int to String: String(IntVariableName);
  -String to Int: Int(StringVariableName);

• enum

  enum Type{
       case apple
       case orange
       case banana
  }
  var type = Type.banana
  //var type:Type = .banana

• A non-parameter constructor

  convenience init(){
       init(name: "hello", seats: 2, type: .sports)
  }    
  
  or
  
  convenience init(name: String){
       init(name: "hello", seats: 2, type: .sports)
  }

  -Then we can use two approaches to init;

• inherit
  -Tesla is son, Car is fater;

     class Tesla:Car{  
     }  

• Override

   class fish:animal{
       override func breathe (){
             super.breathe()
             //do sth. here
       }
  }   

• optional
  -Like ? or !;
  -var destination:String?;
  -It means at the beginning, there is no initialise value for it;
  -If we want to use destination into print which we have mention above, we need to use destination! as a wrap action or nil;

  -Tips: But if we have not give destination a value, we print it, the code will crush, because there is no value for destination, but we try to wrap which means forced to figure out "?";

• Use 'destination?' as a code
  -if let;

   if let dest = destination{ 
        print(dest)
   }

  -So we don't need to use destination! every time;

• import CoreLocation
  -Apple's own position package;

• Get the current location
  -let locationManager = CLLocationManager()
  -There is no actions in CLLocationManager;
  -The actions claims are the another protocol(CLLocationManagerDelegate);

• Some function appropriates Xcode to show it when the app appears

     override func viewWillAppear(_ animated: Bool) {
        <#code#>
     }   

• When the device wants to use the location, device may request the agreement from the device
  -Device may request the agreement from the device;
  -locationManager.requestWhenInUseAuthorization();

• Set accuracy of location
  -locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;

• Request for location
  -There is a description when click this one - request one-time/all the time(we can change it);
  -locationManager.requestLocation();

• A class has 3 parameters: property, method, actions

• delegate
  -Delegate is the same usage as Interface, just method name, no details;
  -All optional method can be chosen optional, others are must be used;

     class ViewController: UIViewController, CLLocationManagerDelegate{
     }

• didUplocation
  -It is used after we want to requestLocation;
  -It means if we use requestLocation, it will use didUplocation;

     func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
          <#code#>
     }
     //all requests are stored in an array - [CLLocation] which concerns latitude & longitude;  

• Get current position's lat and lon
  -let lat = locations[0].coordinate.latitude;
  -let lon = locations[0].coordinate.longitude;
  -Remember to add this line into viewdidload: locationManager.delegate = self;

• dictionary
  -(key:value): let dict : [String: String] = ["name":"Grace", "age":"12", "gender":"female"];
  -We can get one of an array by 'arr[index]', we can get one of dictionary's value by dict["name"];
  -dict[key] = value;
  -It can be set as [String:Any] that means "name":Grace but "age":12 is also allowed, the value can be any variables;

• SwiftyJSON
  -If we want to analyse JSON which we get from api, we can use SwiftyJSON on cocoapod;
  -When we use SwiftyJSON to anaylse, we need to get value;
  -.String: if the value of "name" is null, the whole one maybe null;
  -.StringValue: it will be a ' ', not null;

• Computed variable
  -The variable of this type cannot be detected automatically, so we need to give variables as a original value;

  var iconName:String{
      //the value of this iconName will change when the other changes;   
        switch (condition) {
        case 0...100:
            return "cloudy"
        case 100...200:
            return "fog"
        default:
            return: "sunny"
  } 

• round()
  -4 throw, 5 add;

• extention
  -We can create an extention viewcontroller outside of the main viewcontroller to avoid inconvenience of the confusing code;

• prepare in second viewController on segue
  -There will be a prepare method on the second viewController about segue;

• Switch one controller to another one

     override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destination.
        // Pass the selected object to the new view controller.
        if segue.identifier == "selectCity"{
            segue.destination as! SelectCityController
        }
    }

• as as! as?
  -Int(3.2) = 3.2 as Int: Up transfer, from sub to father;
  -as! and as?: Down transfer, from father to son, one is must, one is optional - upcasting;

• Individual delegate

     protocol SelectCityDelegate {
           func didChangeCity()
     }
     var delegate:SelectCityDelegate?
     @IBAction func changeCityBtn(_ sender: Any) {
           delegate?.didChangeCity()
     }
     vc.delagate = self; 

• Let current page disapper
  -dismiss(animated: true, completion: nil)

• Let different cell show different content by indexPath
  -cell.todoTextLabel.text = todos[indexPath.row].text

• Let the arrow become the first responder as blingbling
  -todoInput.becomeFirstResponder()

• Let the Navigation Controller pop any other controller
  -navigationController?.popViewController(animated: true)

• Delete an item from an array
  -todos.remove(at: indexPath.row)

• ``