以编程方式访问自动布局约束 [英] Access Auto Layout Constraint Programmatically

问题描述

我有一个有很多子视图的视图，我将这些视图称为superview，子视图A，子视图B，子视图C等。

I have a view that has a lot of subviews, I will refer to these views as superview, subview A, subview B, subview C, etc.

所以我需要访问我在subView A上设置的尾随空间约束来superview并修改它。此约束将出现在superview.constraints中。

So I need to access the trailing space constraint I set on subView A to superview and modify it. This constraint would appear in superview.constraints.

但是，所有子视图都在它们和superview之间设置了前导/尾随空间约束。

However, all the subviews have leading/trailing space constraints set between them and the superview.

所以，如果我记录superview.constraints，它看起来像这样：

So, if I log superview.constraints, it would look like this:

<__NSArrayM 0xac744e0>(
<NSLayoutConstraint:0x98f3500 H:|-(0)-[UILabel:0x98f2190]   (Names:     '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3540 H:[UILabel:0x98f2190]-(20)-|   (Names:   '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3580 V:[UILabel:0x98f2190]-(-4)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f35c0 V:[UIView:0x98f2770]-(42)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3600 H:[UIView:0x98f2770]-(20)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3640 H:|-(0)-[UIView:0x98f2770]   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3680 H:|-(0)-[UIView:0x98f2610]   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f36c0 H:[UIView:0x98f2610]-(0)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3700 V:[UIView:0x98f2610]-(1)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3740 V:[UIView:0x98f2920]-(107)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3780 H:[UIView:0x98f2920]-(20)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f37c0 H:|-(0)-[UIView:0x98f2920]   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3800 H:[UIButton:0x98f19c0]-(178)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3840 V:[UIButton:0x98f19c0]-(55)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3880 H:|-(0)-[UILabel:0x98f2a80]   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f38c0 V:[UILabel:0x98f2a80]-(109)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3900 H:[UILabel:0x98f2a80]-(20)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3940 H:|-(171)-[UIButton:0x98f2ff0]   (Names: '|':HeaderReusableView:0x98f1f40 )>,
<NSLayoutConstraint:0x98f3980 V:[UIButton:0x98f2ff0]-(55)-|   (Names: '|':HeaderReusableView:0x98f1f40 )>

）

我不知道哪个约束是我想要的。

I have no idea which constraint is the one I want.

推荐答案

好的我明白了。
NSLayoutConstraint有一个名为firstItem的属性和一个属性secondItem。这些是设置约束的视图。

Ok I figured it out. NSLayoutConstraint has a property named firstItem and a property secondItem. These are the views that the constraints are set on.

通常，secondItem将是视图本身。因此，view.constraints [0] .secondItem是视图。

Usually the secondItem would be the view itself. Thus, view.constraints[0].secondItem is view.

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