swift - 淡入链动画不起作用 : only view fades in

Question

我正在尝试使用动画链中的淡入淡出来按顺序淡入我的对象。首先，我使 View 淡入，然后其余标签也应效仿。标签位于堆栈 View 中，其 alpha 为 1.0。我确保所有其他 alpha 值都从零开始。这是我的功能:

func fadeIn() {
    UIView.animate(withDuration: 0.5, delay: 0.0, options: UIView.AnimationOptions.curveEaseIn, animations: {
        self.view.alpha = 1.0
    }, completion: { finished in
        if finished {
            UIView.animate(withDuration: 0.5, delay: 0.0, options: UIView.AnimationOptions.curveEaseIn, animations: {
                self.gameOverLabel.alpha = 1.0
            }, completion: { finished in
                if finished {
                    UIView.animate(withDuration: 0.5, delay: 0.0, options: UIView.AnimationOptions.curveEaseIn, animations: {
                        self.scoreLabel.alpha = 1.0
                    }, completion: { finished in
                        if finished {
                            UIView.animate(withDuration: 0.5, delay: 0.0, options: UIView.AnimationOptions.curveEaseIn, animations: {
                                self.highScoreLabel.alpha = 1.0
                            }, completion: { finished in
                                if finished {
                                    UIView.animate(withDuration: 0.5, delay: 0.0, options: UIView.AnimationOptions.curveEaseIn, animations: {
                                        self.restartButton.alpha = 1.0
                                    }, completion: nil)
                                    //breakpoint set here
                                }
                            })
                        }
                    })
                }
            })
        }
    })
}

我在所有动画完成后设置了一个断点(如上所示)并且所有 alpha 值为 1.0。然而，该设备只给我一个空白的白色屏幕。这是怎么回事？

附注该函数在 View Controller 出现后立即调用:

view.present(vc, animated: false, completion: {
    vc.fadeIn()
})

Answer 1

尝试将 .layoutSubviews 选项添加到您的动画中。像这样:

UIView.animate(withDuration: 1.0, delay: 0.0, options: UIView.AnimationOptions.layoutSubviews, animations: {
    // animate here
})

根据苹果的文档，此选项的作用是:

Lay out subviews at commit time so that they are animated along with their parent.

可能由于已呈现， subview 在提交时尚未布局。