Swift中的非布爾if語句/ Obj-C閉包

Question

我一直在嘗試將教程https://github.com/fastred/CustomScrollView從Objective-C轉換為Swift，但是我被困在一些地方。

在Objective-C中，它具有以下屬性：

@property (nonatomic, weak) UIDynamicItemBehavior *decelerationBehavior;
@property (nonatomic, weak) UIAttachmentBehavior *springBehavior;

然后具有if語句：

if self.decelerationBehavior && !self.springBehavior { ... }

由於這些顯然不是Bool的，這在Swift中意味着什么？

---

void(^solveForY)(CGPoint*) = ^(CGPoint *anchor) {
    if (deltaY != 0) {
        anchor->y = a * anchor->x + b;
    }
};

這似乎是一種關閉，我嘗試使用以下方法將其轉換為Swift：

func solveForY(_ anchor: inout CGPoint) { if deltaY != 0 { anchor.y = a * anchor.x + b } }

---

__weak typeof(self)weakSelf = self;

decelerationBehavior.action = ^{
    CGRect bounds = weakSelf.bounds;
    bounds.origin = weakSelf.dynamicItem.center;
    weakSelf.bounds = bounds;
};

---

但是轉換后的應用程序的行為與原始行為完全不同。 有人可以告訴我如何將其轉換為Swift嗎？

Answer 1

如果我正確地解釋了所有這些，那么我將在Swift中執行以下操作：

var decelerationBehavior: UIDynamicItemBehavior?
var springBehavior: UIAttachmentBehavior?

// the if statement in Objective-C is checking for nil. In Objective-C nil == 0 == false
if let decelerationBehavior = decelerationBehavior, let springBehavior = springBehavior { ... }

let solveForY: (CGPoint) -> () = { (anchor) in
    if deltaY != 0 {
        anchor.y = a * anchor.x + b;
    }
}

decelerationBehavior.action = { [weak self] in
    if let weakSelf = self {
        CGRect bounds = weakSelf.bounds
        bounds.origin = weakSelf.dynamicItem.center
        weakSelf.bounds = bounds
    }
}