Swift闭包(7)
2020-07-12 本文已影响0人
_菩提本无树_
教程目录
与OC一样的内容不重复介绍
闭包
闭包其实和OC中的Block差不多,作用是一样的.下面说一下主要的用法和注意事项.
所有要说的话全在代码里
闭包的表现形式
{ (parameters) -> return type in
statements
}
定义全局的闭包
import UIKit
class BlockViewController: UIViewController {
//定义一个全局的无参无返回值的block
let block = {() -> () in
print("调用无参无返回值的block");
}
//有参无返回值
let blockParam = {(s: String) -> () in
print("调");
}
//无参有返回值
let blockRuturn = {() -> String in
return "无参数有返回值"
}
//有参数有返回值
let blockParamRuturn = {(s: String) -> (String) in
return "返回值"+s
}
override func viewDidLoad() {
super.viewDidLoad()
block();
blockParam("有参数");
// Do any additional setup after loading the view.
}
}
闭包作为参数
import UIKit
class BlockViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
blockTest();
blockAsParam(str: "字符串", success: {
//第一个闭包
}, error: {
//正常情况blockTwo会被省略掉,但是我不省略,否则看起来代码不容易辨识,当然看个人情况
})
blockAsParamAndParam(successBlock: { (content, status) in
print("\(content)状态码\(status)")
}, errorBlock: {(content,status) in
print("\(content)状态码\(status)")
})
blockParamAndReturn(successBlock: { (successContent, status) -> (String) in
let str = "\(successContent)状态码为\(status)返回告诉他成功了我很高兴"
return str;
},errorBlock: { (errorContent, status) -> (String) in
let str = "\(errorContent)状态码为\(status)返回告诉他失败了无所谓,但是需努力"
return str;
})
///逃逸闭包
blockEscapingTest();
// Do any additional setup after loading the view.
}
func blockTest() {
//定义一个简单的局部block,
let appendBlock = {(orignStr: String,appendStr: String) -> String in
return orignStr + appendStr;
}
let orginStr = "原始字符串";
let appendStr = "新添加的字符串";
let newStr = appendBlock(orginStr,appendStr);
print(newStr);
//通过上面的例子可以多得出一个结论,Swift是值传递
//调用全局的block
block();
blockParam("调用有参无返回值的block");
print(blockRuturn());
print(blockParamRuturn("有参数"));
}
//无参数无返回值闭包作为参数,开发中很常见的,block: () -> ()闭包,blockTwo: ()闭包,一般把闭包写在参数的后面
func blockAsParam(str:String,success: () -> (),error: ()->()) -> () {
success();
error();
}
//有参数无返回值闭包作为参数,开发中很常见的,block: (String,Int) -> ()闭包
func blockAsParamAndParam(successBlock: (String,Int) -> (),errorBlock: (String,Int) -> ()) -> () {
successBlock("成功了",200);
errorBlock("失败了",404);
}
//有参数有返回值闭包作为参数,开发中很常见的,block: (String,Int) -> ()闭包
func blockParamAndReturn(successBlock: (String,Int)->(String),errorBlock: (String, Int)->(String)) -> () {
let success = successBlock("成功了",200);
let error = errorBlock("失败了",404);
print(success);
print(error);
}
//返回一个block闭包
//如果单纯返回一个参数这么写 func returnBlock() -> (){}
//如果返回一个函数参数这么写 func returnBlock() -> ()->Int{},后面的()->Int相当于一个无参带Int返回值的函数
//其实闭包和函数的写法非常类似
func returnBlock() -> ()->Int {
let block = {()->Int in
return 10;
}
return block;
}
//返回一个函数
func returnFunc() -> ()->() {
func blockT ()->(){
}
return blockT;
}
///有一种情况当闭包作为参数,需要在函数结束后过段时间在执行,这种是逃逸闭包这个时候需要使用@escaping关键字修饰
///使用了这个关键字那么所有使用self的必须显示的使用self不能隐式了,就是必须把self写出来
func blockEscaping(success: @escaping ()->()) -> () {
//将success赋值给block,在合适的时机调用block,blockEscaping的回调正常执行
block = success;
}
func blockEscapingTest() -> () {
blockEscaping {
print("测试逃逸");
};
//不执行block(),上面的block是不执行回调的
block();
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
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.
}
*/
}
闭包的值捕获
//
// BlockViewController.swift
// SwiftCourse
//
// Created by 董德帅 on 2020/7/11.
// Copyright © 2020 九天. All rights reserved.
//
import UIKit
class BlockViewController: UIViewController {
//定义全局属性
var globalNum = 12;
var globalStr:String? = "全局字符串";
static var globalStaticStr = "静态全局变量";
override func viewDidLoad() {
super.viewDidLoad()
///值捕获
blockCapture();
// Do any additional setup after loading the view.
}
///闭包的值捕获
func blockCapture() -> () {
var num = "测试";
let testBlock = {() -> () in
num.append("新的字符串");
self.globalNum = 123;
self.globalStr = "修改全局字符串"
BlockViewController.globalStaticStr = "修改静态全局字符串";
}
testBlock();
//和OC不一样,局部变量可以直接被修改,不需要被修饰.全局的可以被直接修改.
//所以在Swift中捕获的是对象不是值了.
print(num,self.globalStr,self.globalNum,BlockViewController.globalStaticStr);
//测试值的捕获.可以发现即使已经出了作用域,值还是被block一直持有,未被释放
let blockTest = blockCaptureTest(oraginNum: 10);
blockTest();//打印为110
blockTest();//打印为120
blockTest();//打印为130
}
///测试值捕获
func blockCaptureTest(oraginNum: Int) -> ()->() {
var currentNum = 100;
let testBlock = {()->() in
//这里这个block捕获了currentNum和oraginNum两个值
currentNum += oraginNum;
print(currentNum);
}
//将block返回
return testBlock;
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
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.
}
*/
}
闭包的循环引用
//
// BlockViewController.swift
// SwiftCourse
//
// Created by 董德帅 on 2020/7/11.
// Copyright © 2020 九天. All rights reserved.
//
import UIKit
class BlockViewController: UIViewController {
//定义全局属性
var globalStr:String? = "全局字符串";
/**
全局block,这里使用lazy的作用是确保self已经被初始化了,否则在全局的闭包中不能使用self.
这个时候使用blockGlobal这个闭包就会引起循环引用.self强引用blockGlobal,blockGlobal强引用self
*/
lazy var blockGlobal: () -> String = {()->(String) in
//这是一个全局的block
//在里面调用self的属性
let n = self.globalStr ?? "22";
return n;
}
///解决的办法使用弱引用或者新增的一个属性无主引用,这里使用弱引用修饰
///将需要弱引用的使用weak修饰[weak weakSelf = self,weak delegate = self.delegate]这是个list
lazy var blockGlobalWeak: () -> String = {[weak weakSelf = self]()->(String) in
//这是一个全局的block
//在里面调用self的属性
if let weakS = weakSelf {
let n = weakS.globalStr ?? "22";
return n;
}else{
return "空的"
}
}
///使用无主引用
///将需要使用无主引用的使用unowned修饰[unowned weakSelf = self],这是个list
lazy var blockGlobalUnowned = {[unowned self]()->String in
//这是一个全局的block
//在里面调用self的属性
let n = self.globalStr ?? "22";
return n;
}
override func viewDidLoad() {
super.viewDidLoad()
///循环引用
blockCirculate();
// Do any additional setup after loading the view.
}
///既然写到了闭包,那么必不可少的一件事就是循环引用,Swift同样会有
func blockCirculate() -> () {
//下面调用的这个block是会引起循环引用的
let title = blockGlobal();
//调用下面的两个block不会出现循环引用的问题
let titleOne = blockGlobalWeak();
let titleTwo = blockGlobalUnowned();
print(title);
}
///deinit相当于dealloc
deinit {
print("被释放")
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
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.
}
*/
}
