将 (Block: Objective-C ) 翻译成 (Closure: Swift) 请验证我的代码

Question

我正在尝试将 ObjC 代码翻译成 swift 版本。我在 'Block' 和 'Closure' 之间有一些混淆点。

如图所示，有一个"completion:^(...)"让我无解。
以及"if(halfway) halfway(finished)"和"if(completion) completion(finished)"是什么意思？为什么存在“;”在控制流之后？

非常感谢您的帮助和指导。

伊桑·乔

ObjC 版本：

- (void)flipTransitionWithOptions:(UIViewAnimationOptions)options halfway:(void (^)(BOOL finished))halfway completion:(void (^)(BOOL finished))completion
{
    CGFloat degree = (options & UIViewAnimationOptionTransitionFlipFromRight) ? -M_PI_2 : M_PI_2;

CGFloat duration = 0.4;
CGFloat distanceZ = 2000;
CGFloat translationZ = self.frame.size.width / 2;
CGFloat scaleXY = (distanceZ - translationZ) / distanceZ;

CATransform3D rotationAndPerspectiveTransform = CATransform3DIdentity;
rotationAndPerspectiveTransform.m34 = 1.0 / -distanceZ; // perspective
rotationAndPerspectiveTransform = CATransform3DTranslate(rotationAndPerspectiveTransform, 0, 0, translationZ);

rotationAndPerspectiveTransform = CATransform3DScale(rotationAndPerspectiveTransform, scaleXY, scaleXY, 1.0);
self.layer.transform = rotationAndPerspectiveTransform;

[UIView animateWithDuration:duration / 2 animations:^{
    self.layer.transform = CATransform3DRotate(rotationAndPerspectiveTransform, degree, 0.0f, 1.0f, 0.0f);
} completion:^(BOOL finished){
    if (halfway) halfway(finished);
    self.layer.transform = CATransform3DRotate(rotationAndPerspectiveTransform, -degree, 0.0f, 1.0f, 0.0f);
    [UIView animateWithDuration:duration / 2 animations:^{
        self.layer.transform = rotationAndPerspectiveTransform;
    } completion:^(BOOL finished){
        self.layer.transform = CATransform3DIdentity;
        if (completion) completion(finished);
    }];
}];


</p>

<hr>

<p>My Swift Version:
    func flipTransitionWithOptions(var options:UIViewAnimationOptions, _halfway halfway:((finished: Bool) -> Void)?, _completion completion:((finished: Bool) -> Void)?) {
        var degree: CGFloat!
        if(options == UIViewAnimationOptions.TransitionFlipFromRight){
            degree = CGFloat(-M_PI_2)
        } else {
            degree = CGFloat(M_PI_2)
        }
        var duration: CGFloat = 0.4
        var distanceZ: CGFloat = 2000
        var translationZ: CGFloat = self.frame.width / 2
        var scaleXY: CGFloat = (distanceZ - translationZ) / distanceZ</p>

    var rotationAndPerspectiveTrabsform: CATransform3D = CATransform3DIdentity
    rotationAndPerspectiveTrabsform.m34 = 1.0 / (-distanceZ)
    rotationAndPerspectiveTrabsform = CATransform3DTranslate(rotationAndPerspectiveTrabsform, 0, 0, translationZ)
    rotationAndPerspectiveTrabsform = CATransform3DScale(rotationAndPerspectiveTrabsform, scaleXY, scaleXY, 1.0)
    layer.transform = rotationAndPerspectiveTrabsform

    UIView.animateWithDuration(0.2, animations: {self.layer.transform = CATransform3DRotate(rotationAndPerspectiveTrabsform, degree, 0.0, 1.0, 0.0)}, completion: {finished in
    self.layer.transform = CATransform3DRotate(rotationAndPerspectiveTrabsform, -degree, 0.0, 1.0, 0.0)
        UIView.animateWithDuration(0.2, animations: {self.layer.transform = rotationAndPerspectiveTrabsform}, completion: {finished in self.layer.transform = CATransform3DIdentity})
    })

}

Answer 1

在您未使用 finished 参数的任何情况下，将参数名称 finished 替换为 _。在 Objective C 版本中，finished 被传递给您从 Swift 翻译中省略的附加函数处理程序。

swift中的

_表示该参数未使用。在 Swift 文档中，它向您展示了闭包中的许多项目如果未使用则可以省略，因此请务必研究 Swift 语言指南以了解这些细微差别和选项。

^{ } 格式仅适用于 ObjC，Swift 中不需要。只是 { }

看起来开发人员添加了行以选择性地调用补充完成处理程序函数（如果它们存在）...称为 halfway 和 completion，分别。它们几乎肯定是函数指针，但 completion 可能不是最佳选择，因为它恰好与函数参数同名。

您应该检查原始代码，看看它们的源代码中是否有名为 halfway 或 completion 的函数或闭包，以确保您没有遗漏一些同样需要的基本代码在完成运行时调用。

将 (Block: Objective-C ) 翻译成 (Closure: Swift) 请验证我的代码

Translating (Block: Objective-C ) to (Closure: Swift) Please verify my code

block

swift