是啥导致两个具有相同自动布局约束的 UITableViewCell 表现不同?
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【中文标题】是啥导致两个具有相同自动布局约束的 UITableViewCell 表现不同?【英文标题】:What causes two UITableViewCells with the same autolayout constraints to behave differently?是什么导致两个具有相同自动布局约束的 UITableViewCell 表现不同? 【发布时间】:2016-11-21 19:36:19 【问题描述】:我正在使用表格中的AFCollectionView,但它没有像我预期的那样呈现。为了调试问题,我创建了另一个具有所需布局的自定义表格单元格,并将其放入 AFCollectionView 单元格中。集合视图单元格仍未正确呈现。
这两个单元都是在没有 xib 或情节提要的情况下构建的,因此我正在努力尝试调试自动布局控制台问题。我知道 UICollectionView 比 UIView 更复杂,但鉴于显示的问题,我什至不确定从哪里开始尝试进行更改。
两个单元格都有以下从 - (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
方法内部调用的 updateConstraints 方法。
[self updateConstraints];
return self;
- (void)updateConstraints
[super updateConstraints];
//Create local versions of the ivars
UILabel *titleLabelP = self.titleLabel;
UIView *bottomViewP = self.collectionView;
NSNumber *bottomViewHeightP = [NSNumber numberWithInteger:self.bottomViewHeight];
//Build the visual constraints
NSDictionary *views = NSDictionaryOfVariableBindings(titleLabelP, bottomViewP);
NSDictionary *metrics = @ @"padding" : @8.0, @"viewHeight": bottomViewHeightP ;
// title and bottom view fill the width of the superview (cell content view)
[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-padding-[titleLabelP]-padding-|" options:0 metrics:metrics views:views]];
[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-padding-[bottomViewP]-padding-|" options:0 metrics:metrics views:views]];
// title and bottom view are setup vertically with 8px of padding between. The cell should expand to fit the full size of the bottom view.
[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-padding-[titleLabelP]-padding-[bottomViewP(viewHeight)]-padding-|" options:0 metrics:metrics views:views]];
自动布局问题的控制台日志:
2016-11-21 14:19:06.423003 AutoLayoutTableCellTest[71645:4731377] [Warning] Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.
2016-11-21 14:19:06.425136 AutoLayoutTableCellTest[71645:4731377] [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSAutoresizingMaskLayoutConstraint:0x608000096710 h=--& v=--& UITableViewCellContentView:0x7fb87ac1a770.midY == 22.25 (active)>",
"<NSAutoresizingMaskLayoutConstraint:0x6080000966c0 h=--& v=--& UITableViewCellContentView:0x7fb87ac1a770.height == 44.5 (active)>",
"<NSLayoutConstraint:0x608000095860 V:|-(8)-[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1'] (active, names: '|':AFTableViewCell:0x7fb87b050400'CellIdentifier' )>",
"<NSLayoutConstraint:0x608000095900 AFIndexedCollectionView:0x7fb87b051000.height == 150 (active)>",
"<NSLayoutConstraint:0x608000095950 V:[AFIndexedCollectionView:0x7fb87b051000]-(8)-| (active, names: '|':UITableViewCellContentView:0x7fb87ac1a770 )>",
"<NSLayoutConstraint:0x608000095fe0 V:[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1']-(8)-[AFIndexedCollectionView:0x7fb87b051000] (active)>",
"<NSAutoresizingMaskLayoutConstraint:0x608000095180 h=-&- v=--& 'UIView-Encapsulated-Layout-Top' AFTableViewCell:0x7fb87b050400'CellIdentifier'.minY == 0 (active, names: '|':UITableViewWrapperView:0x7fb87b03b800 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x608000095fe0 V:[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1']-(8)-[AFIndexedCollectionView:0x7fb87b051000] (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2016-11-21 14:19:06.425934 AutoLayoutTableCellTest[71645:4731377] [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSAutoresizingMaskLayoutConstraint:0x608000096710 h=--& v=--& UITableViewCellContentView:0x7fb87ac1a770.midY == 22.25 (active)>",
"<NSAutoresizingMaskLayoutConstraint:0x6080000966c0 h=--& v=--& UITableViewCellContentView:0x7fb87ac1a770.height == 44.5 (active)>",
"<NSLayoutConstraint:0x608000095860 V:|-(8)-[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1'] (active, names: '|':AFTableViewCell:0x7fb87b050400'CellIdentifier' )>",
"<NSLayoutConstraint:0x6080000958b0 V:[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1']-(8)-[AFIndexedCollectionView:0x7fb87b051000] (active)>",
"<NSLayoutConstraint:0x608000095900 AFIndexedCollectionView:0x7fb87b051000.height == 150 (active)>",
"<NSLayoutConstraint:0x608000095950 V:[AFIndexedCollectionView:0x7fb87b051000]-(8)-| (active, names: '|':UITableViewCellContentView:0x7fb87ac1a770 )>",
"<NSAutoresizingMaskLayoutConstraint:0x608000095180 h=-&- v=--& 'UIView-Encapsulated-Layout-Top' AFTableViewCell:0x7fb87b050400'CellIdentifier'.minY == 0 (active, names: '|':UITableViewWrapperView:0x7fb87b03b800 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x6080000958b0 V:[UILabel:0x7fb87ac1b670'CURRENT INDEXPATH ROW: 1']-(8)-[AFIndexedCollectionView:0x7fb87b051000] (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
我已经把示例项目放到了github上@https://github.com/propstm/AutoLayoutTableCellTest
使用 COLLECTIONVIEW 编辑以显示单元格的初始化:
- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
if (!(self = [super initWithStyle:style reuseIdentifier:reuseIdentifier])) return nil;
UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
layout.sectionInset = UIEdgeInsetsMake(10, 10, 9, 10);
layout.itemSize = CGSizeMake(100, 100);
layout.scrollDirection = UICollectionViewScrollDirectionVertical;
self.collectionView = [[AFIndexedCollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:CollectionViewCellIdentifier];
[self.collectionView setTranslatesAutoresizingMaskIntoConstraints:FALSE];
self.collectionView.backgroundColor = [UIColor whiteColor];
self.collectionView.showsHorizontalScrollIndicator = NO;
[self.contentView addSubview:self.collectionView];
if(!self.titleLabel)
self.titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(16, 8, self.frame.size.width-8, 20)];
[self.titleLabel setTranslatesAutoresizingMaskIntoConstraints:FALSE];
UIFont *boldFont = [UIFont fontWithName:@".SFUIText-Bold" size:16.0f];
[self.titleLabel setFont:boldFont];
[self addSubview:self.titleLabel];
self.bottomViewHeight = 150;
[self updateConstraints];
return self;
【问题讨论】:
【参考方案1】:通过以下更改,我能够消除这些自动布局警告:
在您的AFTableViewCell
的-initWithStyle:reuseIdentifier:
方法中,在返回之前,将单元格的contentView
的translatesAutoresizingMaskIntoConstraints
属性设置为NO
。
将标题标签添加到单元格的内容视图,而不是单元格本身。
这会导致出现新的警告:
[Warning] Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.
但是,布局似乎更接近您的预期。
【讨论】:
【参考方案2】:每当您以编程方式创建视图并设置自动布局约束时,您必须在添加约束的视图上设置translatesAutoresizingMaskIntoConstraints = false
。如果没有,自动调整掩码将转换为自动布局约束。
在这种情况下,您需要添加类似:
self.titleLabel.translateAutoresizingMaskIntoConstraints = false
self.collectionView.translateAutoresizingMaskIntoConstraints = false
已添加
根据您添加的日志,collectionView 的高度为 150,但 contentView 的高度小于该高度。您必须返回正确的高度UITableViewCell
。
【讨论】:
我已经在单元格的 init 方法中将那部分放在上面。我也将该代码添加到帖子中。我尝试将 NO 替换为 FALSE,仍然没有解决方案。 我正在使用估计的行高。 titleLabel 的高度为 20,collectionView 的高度为 150,因此在我的垂直约束下,我希望自动调整大小的高度约为 200。 你也有填充物。返回所有高度和填充总和的确切高度以上是关于是啥导致两个具有相同自动布局约束的 UITableViewCell 表现不同?的主要内容,如果未能解决你的问题,请参考以下文章