我一直试图弄清楚如何在swift中使用JavaScriptCore.我遇到了问题,但是当我必须处理块作为参数时,似乎块立即运行并且参数获得块的返回值.我究竟做错了什么?
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:
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'"
我在这里遗漏了什么,或者这只是Swift中的一个错误?
编辑:
我现在也尝试过Cast closures/blocks的建议
class Block<T> { let f : T init (_ f: T) { self.f = f } }
接着
ctx.setObject(Block<()->Void> { /*code*/ },forKeyedSubscript: "test")
Thread 1: EXC_BREAKPOINT (code=EXC_I386_BPT,subcode=0x0)
它与Swift如何实现闭包有关.你需要使用@convention(block)来注释闭包是ObjC块.使用unsafeBitCast强制转换它
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