swift – 使用DispatchTime.now()float延迟？

为什么我不能指定等待变量的时间？

我怎么能使用变量？

给定错误>>>

var time : Float = 2.2 // <---time 

@IBACtion func buttonPressed(_ sender: Any) {

    let when = DispatchTime.Now() + 2.2 // <---- THIS IS OKAY
    DispatchQueue.main.asyncAfter(deadline: when){

        print("Hello")
    }

    let whenWhen = DispatchTime.Now() + time // <---- THIS IS NOT OKAY
    DispatchQueue.main.asyncAfter(deadline: whenWhen){

        print("Hello")
    }
}