ios - 为什么这个布局模棱两可？

Question

我有一个带有一些标签和 ImageView 的基本单元格。我使用视觉格式语言添加约束，但在运行时它们变得模棱两可。这是怎么回事？!

[self.constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-15-[_typeLabel]-10-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_typeLabel)]];
[self.constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-15-[_addressLabel]-10-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_addressLabel)]];
[self.constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-15-[_mapImageView]-10-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_mapImageView)]];
[self.constraints addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-11-[_typeLabel]-2-[_addressLabel]-[_mapImageView]-10-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_typeLabel, _addressLabel, _mapImageView)]];

这是我的 _autolayoutTrace:

*<UITableViewCellContentView:0x940dc30>
|   *<UILabel:0x943aab0> - AMBIGUOUS LAYOUT
|   *<UILabel:0x940ead0> - AMBIGUOUS LAYOUT
|   *<UIImageView:0x9445c20> - AMBIGUOUS LAYOUT
<_UITableViewCellSeparatorView:0x9446200>

下面是影响前两个 UILabel 的约束:

(lldb) po [0x943aab0 constraintsAffectingLayoutForAxis:0]
<__NSArrayM 0x975fee0>(
<NSLayoutConstraint:0x940eca0 H:|-(15)-[UILabel:0x943aab0]   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSLayoutConstraint:0x940ecf0 H:[UILabel:0x943aab0]-(10)-|   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSAutoresizingMaskLayoutConstraint:0x9446a70 h=--& v=--& H:[UITableViewCellContentView:0x940dc30(320)]>
)


(lldb) po [0x943aab0 constraintsAffectingLayoutForAxis:1]
<__NSArrayM 0xaa4af10>(
<NSLayoutConstraint:0x9446030 V:|-(11)-[UILabel:0x943aab0]   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSContentSizeLayoutConstraint:0x943a840 V:[UILabel:0x943aab0(17)] Hug:250 CompressionResistance:750>
)


(lldb) po [0x940ead0 constraintsAffectingLayoutForAxis:0]
<__NSArrayM 0x97b4240>(
<NSLayoutConstraint:0x940ed90 H:|-(15)-[UILabel:0x940ead0]   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSLayoutConstraint:0x940ede0 H:[UILabel:0x940ead0]-(10)-|   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSAutoresizingMaskLayoutConstraint:0x9446a70 h=--& v=--& H:[UITableViewCellContentView:0x940dc30(320)]>
)


(lldb) po [0x940ead0 constraintsAffectingLayoutForAxis:1]
<__NSArrayM 0xa985d30>(
<NSLayoutConstraint:0x9446030 V:|-(11)-[UILabel:0x943aab0]   (Names:'|':UITableViewCellContentView:0x940dc30 )>,
<NSLayoutConstraint:0x9446080 V:[UILabel:0x943aab0]-(2)-[UILabel:0x940ead0]>,
<NSContentSizeLayoutConstraint:0x943a840 V:[UILabel:0x943aab0(17)] Hug:250 CompressionResistance:750>,
<NSContentSizeLayoutConstraint:0x9446bb0 V:[UILabel:0x940ead0(33)] Hug:250 CompressionResistance:750>
)

Answer 1

对于模棱两可的布局，您需要设置标签的属性，例如 contentHugging 和 contentCompressionResistance

希望对你有帮助

编辑: 要了解此属性，您可以关注 Cocoa Autolayout: content hugging vs content compression resistance priority