UITableViewCell 的 setSelected 方法中的 animateWithDuration 没有效果

Question

我正在为 UITableViewCell 的 selection/deselection 尝试一个简单的动画，如下所示：

- (void)setSelected:(BOOL)selected animated:(BOOL)animated {

    [UIView animateWithDuration: 0.5 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:^{

        tabConstraint.constant = selected ? 40 : 20;

    } completion:nil];
}

将调用动画块中的代码，但它不是动画。一切正常，但根本没有任何动画。我怎样才能使单元格选择动画化？

Answer 1

每次更新自动布局约束时，都必须调用 layoutIfNeeded，

- (void)setSelected:(BOOL)selected animated:(BOOL)animated {


    [UIView animateWithDuration: 0.5 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:^{

        tabConstraint.constant = selected ? 40 : 20;
        [self layoutIfNeeded];

    } completion:nil];
}

Answer 2

您需要在 animations 块中调用 layoutIfNeeded。查看关于此问题的已接受答案以了解更多详细信息：How do I animate constraint changes?

Answer 3

您需要在动画块中调用 layoutIfNeeded():-)

- (void)setSelected:(BOOL)selected animated:(BOOL)animated {

    tabConstraint.constant = selected ? 40 : 20;
    [UIView animateWithDuration: 0.5 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:^{
        whateverTabYouHaveHere.layoutIfNeeded()
    } completion:nil];
}