ios - 如何正确地将 UIView 连续移动到 UIButtons 下面

Question

我正在制作一种标签栏，其下方有一个指示器，指示选择了哪个标签。我的 View 层次结构非常简单:

---------------------------------
|-------------     -------------|
||            |    |           ||
||  Button 1  |    |  Button 2 ||
||____________|    |___________||
| ------------                  |
---------------------------------

我最初将指标前导和尾随约束设置为与按钮 1 相同:

self.indicatorLeadingConstraint = [self.indicatorView.leadingAnchor constraintEqualToAnchor:self.firstButton.leadingAnchor];
self.indicatorLeadingConstraint.active = YES;
self.indicatorTrailingConstraint = [self.indicatorView.trailingAnchor constraintEqualToAnchor:self.firstButton.trailingAnchor];
self.indicatorTrailingConstraint.active = YES;

然后我会在点击按钮时更新它们:

self.indicatorLeadingConstraint.active = NO;
self.indicatorLeadingConstraint = [self.indicatorView.leadingAnchor constraintEqualToAnchor:button.leadingAnchor];
self.indicatorLeadingConstraint.active = YES;

self.indicatorTrailingConstraint.active = NO;
self.indicatorTrailingConstraint = [self.indicatorView.trailingAnchor constraintEqualToAnchor:button.trailingAnchor];
self.indicatorTrailingConstraint.active = YES;

这实际上工作正常，但是我在控制台中收到警告:

(
"<NSLayoutConstraint:0x600001332620 H:[UIButton:0x7ffa68556530'First (0)']-(16)-[UIButton:0x7ffa6865e0f0'Second (0)']   (active)>",
"<NSLayoutConstraint:0x600001318a00 IndicatorView.leading == UIButton:0x7ffa6865e0f0'Second (0)'.leading   (active, names: IndicatorView:0x7ffa6865eb20 )>",
"<NSLayoutConstraint:0x600001332760 IndicatorView.trailing == UIButton:0x7ffa68556530'First (0)'.trailing   (active, names: IndicatorView:0x7ffa6865eb20 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600001332620 H:[UIButton:0x7ffa68556530'First (0)']-(16)-[UIButton:0x7ffa6865e0f0'Second (0)']   (active)>

我真的不明白为什么以这种方式移动 View 会对我的两个按钮之间的水平间距约束产生任何影响。

编辑这是最终产品:

Answer 1

重新排列代码，如下所示。我认为它会解决这个问题。尝试过后请告诉我。

IndicatorLeadingConstraint.isActive = false
IndicatorTrailingContraint.isActive = false
IndicatorLeadingConstraint = indicatorView.leadingAnchor.constraint(equalTo: sender.leadingAnchor)
IndicatorTrailingContraint = indicatorView.trailingAnchor.constraint(equalTo: sender.trailingAnchor)
IndicatorTrailingContraint.isActive = true
IndicatorLeadingConstraint.isActive = true