迅捷方块不起作用 [英] Swift blocks not working

问题描述

我一直试图弄清楚如何快速使用JavaScriptCore.但是，当我不得不将块作为参数处理时，我遇到了问题，好像该块立即运行并且该参数获取了该块的返回值.我在做什么错了?

I've been trying to figure out how to use JavaScriptCore in swift. I'm running into problems however when I have to deal with blocks as arguments, seems like the block is run immediately and the arguments gets the return value of the block. What am I doing wrong?

工作目标C代码:

JSContext* context = [[JSContext alloc] initWithVirtualMachine:[[JSVirtualMachine alloc] init]];
context[@"test"] = ^(NSString *string) {
    //code
};

我尝试过的事情:

1:

var ctx = JSContext(virtualMachine:JSVirtualMachine())
var ctx["test"] = {(string:NSString)->() in /*code*/ }

//Gives me "'JSContext' does not have a member named 'subscript'"

2:

var ctx = JSContext(virtualMachine:JSVirtualMachine())
let n: (string: String)->() = {string in /*code*/}

ctx.setObject(n, forKeyedSubscript:"test")

//Gives me "Type '(x: String) -> () does not conform to protocol 'AnyObject'"

3:

var ctx = JSContext(virtualMachine:JSVirtualMachine())
let n: (string: String)->() = {string in /*code*/}

ctx.setObject(n as AnyObject, forKeyedSubscript:"test")

//Gives me "Cannot downcast from '(string: String) -> () to non-@objc protocol type 'AnyObject'"

我在这里丢失了什么吗，还是仅仅是Swift中的错误?

Am I missing something here, or is this just a bug in Swift?

我现在还尝试了铸封/块

class Block<T> {
    let f : T
    init (_ f: T) { self.f = f }
}

然后

ctx.setObject(Block<()->Void> {
        /*code*/
    }, forKeyedSubscript: "test")

此解决方案可让我编译，但会遇到运行时错误:

This solution lets me compile but I get a runtime error:

Thread 1: EXC_BREAKPOINT (code=EXC_I386_BPT, subcode=0x0)

推荐答案

它与Swift实现闭包有关.您需要使用@convention(block)注释闭包是ObjC块.使用unsafeBitCast强制投射

It has something to do with how Swift implement closure. You need to use @convention(block) to annotate that the closure is ObjC block. Use unsafeBitCast to force cast it

var block : @convention(block) (NSString!) -> Void = {
   (string : NSString!) -> Void in 
    println("test")
}

ctx.setObject(unsafeBitCast(block, AnyObject.self), forKeyedSubscript: "test")

来自REPL

swift
Welcome to Swift!  Type :help for assistance.
  1> import Foundation
  2> var block : @convention(block)(NSString!) -> Void = {(string : NSString!) -> Void in println("test")}
block: @convention(block)(NSString!) -> Void =
  3> var obj: AnyObject = reinterpretCast(block) as AnyObject
obj: __NSMallocBlock__ = {} // familiar block type

这篇关于迅捷方块不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！