Swift3.0 function closure and OC Block

Just contact Swift, if there is a wrong point, please correct me. Reprint please indicate the source

• Define a basic function in Swift

// defines a function that receives a string that returns the value of a string type, func test (name:string), string        {return ("  output \ (name)    }// general form return  type {        function Body    }

• The similarity between the basic closure function in Swift and the block in OC
  
• With closed package
  

  //This is the block in OC.void(^test) (NSString *) =^ (NSString *name) {NSLog (@"%@", name);    }; Test (@"Test");//corresponding to Swift with the reference closureLet Test={(_ Name:string) ()inch  //In the back is the function that is processed after the callback, equivalent to the {} after the blockprint (name)} Test ("Test")//General Form{(parameters)ReturnTypeinchCode}

Here the effect of the underline _ is used to ignore the external parameter name, specifically refer to this article http://www.cnblogs.com/bhlsheji/p/4746072.html

• function definition with block parameter in OC

-(void) LoadData: (  void(^) (void)) completetion{    completetion ();}

• function definition with closure parameters in Swift

Func LoadData (completetion: ()), () {       completetion ()    }//

• For a more common example, network data acquisition

//block transfer value in OC-(void) LoadData: (void(^) (Nsarray *)) completetion{//Here for the time being, ignoring the thread, simple processing, focusing on swift closureNSLog (@"time-consuming Operation"); Sleep (2);//Simulating network requestsNsarray*[email protected][@"1",@"2"]; NSLog (@"Main thread Callback"); Completetion (arr); //returns the data obtainedcall: [Self loaddata:^ (Nsarray *callBack) {NSLog (@"%@,%@", callback[0],callback[1]); }]; output: .-Geneva- A  -: -:45.273tessst[3642:187462] Time-consuming Operation .-Geneva- A  -: -:47.345tessst[3642:187462] Main thread update .-Geneva- A  -: -:47.346tessst[3642:187462]1,2//closed packet transfer value in SwiftFunc loaddate (Completion: @escaping (_ Result: [String]), () {//here is a very important parameter @escaping, escape closure//simply put, the closure is called before the end of the function, which is the non-escape closure, where the call exceeds the range of the function, called escape closure .//The general network request is the request after a period of time the closure is executed, so all are escape closures. //all closed Baudumo in Swift3.0 are considered non-escape closures, so they need to be modified with @escapingDispatchqueue.Global(). async {Print ("time consuming Operation \ (thread.current)") Thread.Sleep (fortimeinterval:2) Let JSON=["1","2"] DispatchQueue.main.async {print ("main thread update \ (thread.current)") Completion (JSON)//function after the execution of two seconds, the main line friend callback data, beyond the scope of the function, here is the escape closure, if not @escaping, the compiler is compiled but}}} Main function call Loaddate:loaddate {(callBack)inchPrint ("\ (callBack)")} Output value time consuming operation<nsthread:0x608000069140>{number =1, name =main} main thread update<nsthread:0x608000069140>{number =1, name =main}1,2

• There are often circular references in blocks, as in closures, and there are two common ways to solve them.

//First KindWeak Var weakwelf= Self//the way OC is applied (__weak typedef (WEAKSELF) =self).//It is important to note that you cannot use let because self may release a pointer to nil, which is equivalent to a mutable value//can I use the option to send a message? Unpacking, No! Pringt ("weakself?. View") No"weakself!. View"//because forcing the unpacking will crash once Weakself=nil//second, at the time of the call//[Weak self] identifies that all self in {} is a weak referenceloaddate {[Weak self]inchPrint ( self?. View)}

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Swift3.0 function closure and OC Block