1.oc中的block

ViewController.m

#import "ViewController.h"
#import "HttpTools.h"

@interface ViewController ()

@property (nonatomic, strong) HttpTools *tools;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.tools = [[HttpTools alloc] init];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    // 閉包&控制器&HttpTools對象有沒有形成循環引用
    
    __weak ViewController *weakSelf = self;
    
    [self.tools loadData:^(NSString *jsonData) {
        // NSLog(@"在控制器中,拿到數據:%@", jsonData);
        weakSelf.view.backgroundColor = [UIColor redColor];
    }];
}

- (void)dealloc {
    NSLog(@"ViewController -- dealloc");
}

@end

HttpTools.h

#import <Foundation/Foundation.h>

@interface HttpTools : NSObject

- (void)loadData:(void(^)(NSString *))finishedCallback;

@end

HttpTools.m

#import "HttpTools.h"


@interface HttpTools()

@property(nonatomic ,copy) void (^finishedCallback)(NSString *);

@end

@implementation HttpTools

- (void)loadData:(void (^)(NSString *))finishedCallback
{
    self.finishedCallback = finishedCallback;
    
    // 1.發送網絡的異步請求
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"已經發送了網絡請求:%@", [NSThread currentThread]);
        
        // 2.回到主線程
        dispatch_sync(dispatch_get_main_queue(), ^{
            NSLog(@"回到主線程:%@", [NSThread currentThread]);
            
            // 3.獲取數據, 并且將數據回調出去
            finishedCallback(@"json數據");
        });
        
    });
    
}

@end

2.swift中的閉包

HttpTools.swift

import UIKit

class HttpTools {
    
    var finishedCallback : ((_ jsonData : String) -> ())?
    
    // 閉包類型: (_ 參數列表) -> (返回值類型)
    // @escaping : 逃逸的
    func loadData(_ finishedCallback : @escaping (_ jsonData : String) -> ()) {
        
        self.finishedCallback = finishedCallback
        
        // 1.發送異步網絡請求
        DispatchQueue.global().async {
            print("發送異步網絡請求:\(Thread.current)")
            
            DispatchQueue.main.sync {
                print("回到主線程:\(Thread.current)")
                
                finishedCallback("json數據")
            }
        }
    }
}

ViewController.swift

import UIKit

class ViewController: UIViewController {
    
    var httpTools : HttpTools?
    
    // 在swift中只要是對父類的方法進行重寫, 必須在方法前加上override
    override func viewDidLoad() {
        super.viewDidLoad()
        
        httpTools = HttpTools()
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        
        // 解決循環引用的方案:
        // 解決方案一:
        /*
        weak var weakSelf : ViewController? = self
        httpTools?.loadData({ (jsonData : String) in
            weakSelf?.view.backgroundColor = UIColor.red
        })
        */
        
        // 解決方案二:
        /*
        httpTools?.loadData({[weak self] (jsonData : String) in
            self?.view.backgroundColor = UIColor.red
        })
        */
        
        // 解決方案三:
        // unowned --> unsafe_unretained(野指針)
        httpTools?.loadData({[unowned self] (jsonData : String) in
            self.view.backgroundColor = UIColor.red
        })
        
        
        // 尾隨閉包的概念(不建議)
        // 如果在函數中, 閉包是最后一個參數, 那么可以寫成尾隨閉包
        httpTools?.loadData() {[unowned self] (jsonData : String) in
            self.view.backgroundColor = UIColor.red
        }
        
        // 如果是唯一的參數, 也可以將前面的()省略掉
        httpTools?.loadData {[unowned self] (jsonData : String) in
            self.view.backgroundColor = UIColor.red
        }
    }
    
    
    deinit {
        print("ViewController -- deinit")
    }
}