閉包的介紹

閉包和OC中的block非常相似
OC中的block是匿名的函數(shù)
Swift中的閉包是一個(gè)特殊的函數(shù)
block和閉包都經(jīng)常用于回調(diào)
閉包的使用

block的用法回顧

定義網(wǎng)絡(luò)請(qǐng)求的類
@interface HttpTool : NSObject
- (void)loadRequest:(void (^)())callBackBlock;
@end

@implementation HttpTool
- (void)loadRequest:(void (^)())callBackBlock
{
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"加載網(wǎng)絡(luò)數(shù)據(jù):%@", [NSThread currentThread]);

        dispatch_async(dispatch_get_main_queue(), ^{
            callBackBlock();
        });
    });
}
@end
進(jìn)行網(wǎng)絡(luò)請(qǐng)求,請(qǐng)求到數(shù)據(jù)后利用block進(jìn)行回調(diào)
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    [self.httpTool loadRequest:^{
        NSLog(@"主線程中,將數(shù)據(jù)回調(diào).%@", [NSThread currentThread]);
    }];
}
block寫法總結(jié):
block的寫法:
    類型:
    返回值(^block的名稱)(block的參數(shù))

    值:
    ^(參數(shù)列表) {
        // 執(zhí)行的代碼
    };
使用閉包代替block

定義網(wǎng)絡(luò)請(qǐng)求的類
class HttpTool: NSObject {

    func loadRequest(callBack : ()->()){
        dispatch_async(dispatch_get_global_queue(0, 0)) { () -> Void in
            print("加載數(shù)據(jù)", [NSThread.currentThread()])

             dispatch_async(dispatch_get_main_queue(), { () -> Void in
                callBack()
             })
        }
    }
}
進(jìn)行網(wǎng)絡(luò)請(qǐng)求,請(qǐng)求到數(shù)據(jù)后利用閉包進(jìn)行回調(diào)
    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        // 網(wǎng)絡(luò)請(qǐng)求
        httpTool.loadRequest ({ () -> () in
            print("回到主線程", NSThread.currentThread());
        })
    }
閉包寫法總結(jié):
閉包的寫法:
    類型:(形參列表)->(返回值)
    技巧:初學(xué)者定義閉包類型,直接寫()->().再填充參數(shù)和返回值

    值:
    {
        (形參) -> 返回值類型 in
        // 執(zhí)行代碼
    }
閉包的簡(jiǎn)寫

如果閉包沒有參數(shù),沒有返回值.in和in之前的內(nèi)容可以省略
    httpTool.loadRequest({
        print("回到主線程", NSThread.currentThread());
    })
尾隨閉包寫法:
如果閉包是函數(shù)的最后一個(gè)參數(shù),則可以將閉包寫早()后面
如果函數(shù)只有一個(gè)參數(shù),并且這個(gè)參數(shù)是閉包,那么()可以不寫
    httpTool.loadRequest() {
        print("回到主線程", NSThread.currentThread());
    }
    // 開發(fā)中建議該寫法
    httpTool.loadRequest {
        print("回到主線程", NSThread.currentThread());
    }
閉包的循環(huán)引用

如果在HttpTool中有對(duì)閉包進(jìn)行強(qiáng)引用,則會(huì)形成循環(huán)引用
class HttpTool: NSObject {

    // 定義屬性,來(lái)強(qiáng)引用傳入的閉包
    var callBack : (()->())?

    func loadRequest(callBack : ()->()){
        dispatch_async(dispatch_get_global_queue(0, 0)) { () -> Void in
            print("加載數(shù)據(jù)", [NSThread.currentThread()])

             dispatch_async(dispatch_get_main_queue(), { () -> Void in
                callBack()
             })
        }

        self.callBack = callBack
    }
}
swift中解決循環(huán)引用的方式
    // weak var weakSelf = self;
    // [weak self] () -> () in
    // [unowned self] () -> () in
    httpTool.loadRequest { [unowned self] () -> () in
        self.view.backgroundColor = UIColor.redColor()
        print("回到主線程", NSThread.currentThread());
    }