ios 布尔与 swift
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Boolean with swift
提问by George Asda
This is really confusing. Does anyone have any ideas?
这真的很令人困惑。有没有人有任何想法？
let viewHasMovedToRight == false //initially I want this to be false
then
然后
func moveViewToRight(sender: UIButton!) {
if viewHasMovedToRight == false {
viewHasMovedToRight == true;
UIView.animateWithDuration(
0.75,
animations: {},
completion: { (value: Bool) in
println(" moved")
}
)
}
else {
viewHasMovedToRight == false;
UIView.animateWithDuration(
0.75,
animations:{},
completion:{ (value: Bool) in
println("not moved")
}
)
}
// println("move view")
}
Only the first ifis called.
I cannot re-assign the value back to true...
只有第一个if被调用。我无法将值重新分配回 true...
Something that was so easy on Obj-C now with swift is so frustrating...
现在使用 swift 在 Obj-C 上如此简单的事情是如此令人沮丧......
回答by rob mayoff
You have two problems.
你有两个问题。
One, you are using ==(which tests for equality) where you should be using =(which assigns a value). Two, you are declaring a constant and then trying to assign a new value to it later. You need to declare a variable.
一，您正在使用==（测试相等性）您应该使用的位置=（分配一个值）。第二，您要声明一个常量，然后尝试稍后为其分配一个新值。您需要声明一个变量。
var viewHasMovedToRight = false
...
viewHasMovedToRight = true
Also, most people would find this ifcondition more understandable:
此外，大多数人会发现这种if情况更容易理解：
if !viewHasMovedToRight {
And it would be even simpler if you were to reverse the order of your ifclauses:
如果您要颠倒if子句的顺序，那就更简单了：
if viewHasMovedToRight {
viewHasMovedToRight = false
...
} else {
viewHasMovedToRight = true
...
}
回答by AdamPro13
let viewHasMovedToRight = falsenot let viewHasMovedToRight == false
let viewHasMovedToRight = false不是 let viewHasMovedToRight == false
EDIT: It looks like you use ==instead of =everywhere you are setting the boolean.
编辑：看起来您使用==而不是=在您设置布尔值的任何地方。
回答by casillas
@George, you should use set operator
@George，您应该使用 set 运算符
let viewHasMovedToRight = false
not comparison operator
不是比较运算符
let viewHasMovedToRight == false
回答by paulomatsui
Newbie here. I used to do that mistake all the time, using = both for assign and to compare. Use = to assign and == to compare
新手来了 我曾经经常犯这个错误，使用 = 赋值和比较。使用 = 分配，使用 == 进行比较
