ios - 带有持续时间的 UIView.animate 无法正常工作

Question

UIView.animate 在我的代码的“else”部分不起作用。但是，它在“if”语句中工作得很好。有什么建议可能导致此问题吗？

    if notification.name == UIResponder.keyboardWillShowNotification ||
        notification.name == UIResponder.keyboardWillChangeFrameNotification {

        // Keyboard shows
        self.view.layoutIfNeeded()
        UIView.animate(withDuration: 0.25) {
            self.view.layoutIfNeeded()
            let heightHelper = self.bottomConstraint.constant
            self.bottomConstraint.constant = keyboardRect.height + 20

            self.bottomConstraintEmail.constant += keyboardRect.height + 20 - heightHelper
            self.anmeldenLabel.alpha = 0
            self.logoConstraint.constant = 45
        }
    } else {
        // Keyboard hides
        self.view.layoutIfNeeded()
        UIView.animate(withDuration: 0.5) {
            self.view.layoutIfNeeded()
            self.bottomConstraintEmail.constant = 337
            self.bottomConstraint.constant = 255.5
            self.logoConstraint.constant = 60
            self.anmeldenLabel.alpha = 1
        }
    }

Answer 1

@Don 完全正确:layoutIfNeeded() 应该在设置新约束后调用。

这应该可以正常工作:

if notification.name == UIResponder.keyboardWillShowNotification ||
    notification.name == UIResponder.keyboardWillChangeFrameNotification {

    // Keyboard shows
    let heightHelper = self.bottomConstraint.constant
    self.bottomConstraint.constant = keyboardRect.height + 20

    self.bottomConstraintEmail.constant += keyboardRect.height + 20 - heightHelper
    self.anmeldenLabel.alpha = 0
    self.logoConstraint.constant = 45

    UIView.animate(withDuration: 0.25) {
        self.view.layoutIfNeeded()
    }
} else {
    // Keyboard hides
    self.bottomConstraintEmail.constant = 337
    self.bottomConstraint.constant = 255.5
    self.logoConstraint.constant = 60
    self.anmeldenLabel.alpha = 1

    UIView.animate(withDuration: 0.5) {
        self.view.layoutIfNeeded()
    }
}