Swift Learning Day 15th: Closures

Closure Closure Package Introduction

• Closures are very similar to block in OC
  • Block in OC is an anonymous function
  • Closures in Swift are a special function
  • Block and closures are often used for callbacks
• Note: Closures and blocks, the first use may not be used to its syntax, you can follow the use of a simple closure, with the depth of learning, slowly grasp its flexible use of methods.

A review of the usage of block in closures

• Classes that define network requests

 @interface httptool: nsobject-(void) Loadrequest: (void (^) ()) Callbackblock;  @end  @implementation httptool-(void) Loadrequest: (void (^) ()) callbackblock{dispatch_async (Dispatch_get_global_queue (0 , 0), ^{nslog (@ "Load network data:%@", [ Span class= "hljs-built_in" >nsthread CurrentThread]); dispatch_async (Dispatch_get_main_queue (), ^{Callbackblock ();});});  @end             

• Make network requests, request to data and use block for callback

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{    [self.httpTool loadRequest:^{        NSLog(@"主线程中,将数据回调.%@", [NSThread currentThread]);
 self.view.backgroundColor = [UIColor redColor]; }];}

• Block notation Summary:

block的写法:    类型:    返回值(^block的名称)(block的参数)    值:    ^(参数列表) {        // 执行的代码    };
Note: In the block in the OC above, set in block statement blocksself.view.backgroundColor = [UIColor redColor];不会产生循环引用，原因是，：

控制器中属性定义HttpTool，则控制器会对HttpTool有一个强引用，在block语句块中会对外部引用的变量产生一个强引用，所以block对控制器有一个强引用，但HttpTool不会对block产生一个强引用，所以没有形成闭环，不会产生循环引用。若是解决循环引用可以用：__weak typeof(self) weakSelf = self;typeof(self)意思是取self的类型，所以也可以：__weak vc *weakSelf = self。

Swift Learning Day 15th: Closures