设置依赖于父视图框架的约束

Question

我想设置一些宽度约束，这取决于超级视图的宽度。事实上，我想使用自动布局，但我需要访问 superviews 框架来计算我的子视图的宽度。我所有的子视图都添加到 UIView 而不是视图控制器。

我在构造函数中设置了约束，但我想在updateConstraints中更改它们。

构造函数：

nfloat initialWidth = (nfloat)Math.Round((Bounds.Size.Width / 7) - (nfloat)(Math.Ceiling(Bounds.Size.Width % 7) / 2));
container0WidthConstraint = NSLayoutConstraint.Create (container0, NSLayoutAttribute.Width, NSLayoutRelation.Equal, null, NSLayoutAttribute.NoAttribute, 1, initialWidth);
container1WidthConstraint = NSLayoutConstraint.Create (container1, NSLayoutAttribute.Width, NSLayoutRelation.Equal, null, NSLayoutAttribute.NoAttribute, 1, initialWidth);

AddConstraints (new NSLayoutConstraint[] { container0WidthConstraint, container1WidthConstraint });

updateConstraints:

public override void UpdateConstraints ()
{
    nfloat desiredItemWidth = (nfloat)Math.Round(Bounds.Size.Width / 7);
    nfloat remainingWidth = Bounds.Size.Width - desiredItemWidth * 5;

    if (remainingWidth % 2 == 0) {
        // even
        container0WidthConstraint.Constant = remainingWidth / 2;
        container1WidthConstraint.Constant = remainingWidth / 2;
    } else {
        // odd
        container0WidthConstraint.Constant = (nfloat)Math.Floor(remainingWidth / 2);
        container1WidthConstraint.Constant = (nfloat)Math.Ceiling(remainingWidth / 2);
        }

    base.UpdateConstraints ();
}

代码在 C# 中，但我仅将其添加为附加信息。基本上，我想将屏幕分成大小相等的视图。我发现唯一可行的方法是通过如上所示的计算。

我需要Bounds.Size.Width，但调试时它总是空的。设置后如何添加取决于超级视图框架的约束？

编辑：

我认为这对我不起作用的主要原因是它被添加为子视图，因此自动布局系统尚未完成。我应该在哪里放置layoutIfNeeded 还是应该使用layoutSubviews？尝试后一种时，我收到错误“执行 -layoutSubviews 后仍需要自动布局”。那么我应该在哪里放置我的约束或者我应该如何设置我的视图层次结构？

自动布局错误：

"<NSLayoutConstraint:0x7bd11540 H:|-(0)-[UIView:0x7bd16b90]   (Names: '|':TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0 )>",
    "<NSLayoutConstraint:0x7bd11660 H:[UIView:0x7bd16b90]-(0)-[UIView:0x7bd166a0]>",
    "<NSLayoutConstraint:0x7bd114f0 H:[UIView:0x7bd166a0]-(0)-[UIView:0x7bd16a10]>",
    "<NSLayoutConstraint:0x7bd114c0 H:[UIView:0x7bd16a10]-(0)-[UIView:0x7bd163f0]>",
    "<NSLayoutConstraint:0x7bd11490 H:[UIView:0x7bd163f0]-(0)-[UIView:0x7bd15f90]>",
    "<NSLayoutConstraint:0x7bd11460 H:[UIView:0x7bd15f90]-(0)-[UIView:0x7bd15d80]>",
    "<NSLayoutConstraint:0x7bd11410 H:[UIView:0x7bd15d80]-(0)-[UIView:0x7bd15ad0]>",
    "<NSLayoutConstraint:0x7bd113e0 H:[UIView:0x7bd15ad0]-(0)-|   (Names: '|':TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0 )>",
    "<NSLayoutConstraint:0x7bd115c0 UIView:0x7bd16b90.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd11820 UIView:0x7bd166a0.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd11850 UIView:0x7bd16a10.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd11880 UIView:0x7bd163f0.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd118b0 UIView:0x7bd15f90.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd11270 UIView:0x7bd15d80.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7bd11240 UIView:0x7bd15ad0.width == 0.142857*TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0.width>",
    "<NSLayoutConstraint:0x7b8d6d60 H:|-(0)-[TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0]   (Names: '|':UIView:0x7bc3e1e0 )>",
    "<NSLayoutConstraint:0x7b8ce180 H:[TestSevenEquallySpaced_SevenEquallySpacedViews:0x7bd255e0]-(0)-|   (Names: '|':UIView:0x7bc3e1e0 )>",
    "<NSAutoresizingMaskLayoutConstraint:0x7bd018b0 h=-&- v=-&- UIView:0x7bc3e1e0.height == UIWindow:0x7bc3e710.height>",
    "<NSAutoresizingMaskLayoutConstraint:0x7bd00ea0 h=--- v=--- V:[UIWindow:0x7bc3e710(1024)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7bd11410 H:[UIView:0x7bd15d80]-(0)-[UIView:0x7bd15ad0]>

Answer 1

您应该将这些视图限制为视图的宽度，而不是根据它计算的常数。

在 Objective-c 中看起来像

[NSLayoutConstraint constraintWithItem:container0
                             attribute:NSLayoutAtrributeWidth
                             relatedBy:NSLayoutRelationEqual
                                toItem:self
                             attribute:NSLayoutAttributeWidth
                            multiplier:(1.0f/7.0f)
                              constant:0];

这将为您提供一个始终为其父视图宽度的 1/7 的视图。

我猜在 C# 中会是这样

NSLayoutConstraint.Create (container0, NSLayoutAttribute.Width, NSLayoutRelation.Equal, this, NSLayoutAttribute.Width, (1/7), 0);