我在正在加载到表格视图单元格中的字段上使用自动布局。对于每个单元格，我清除contentView中的所有子视图，并根据我需要的字段类型加载我自己的视图。大多数细胞都很好，但当这个细胞进入视野时，我得到一个例外。
以下是单元格的代码：
UILabel *questionText = [[UILabel alloc] init];
questionText.text = self.field.questionText;
questionText.font = font;
questionText.numberOfLines = 0;
questionText.adjustsFontSizeToFitWidth = NO;
questionText.lineBreakMode = NSLineBreakByWordWrapping;
[questionText setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.contentView addSubview:questionText];
UIView *listContainer = [[UIView alloc] init];
listContainer.backgroundColor = [UIColor whiteColor];
listContainer.layer.cornerRadius = 8;
listContainer.layer.borderWidth = 1.0;
[listContainer setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.contentView addSubview:listContainer];
// Get the views dictionary
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(questionText, listContainer);
//Create the constraints using the visual language format
NSString *format = @"V:|-10-[questionText]-10-[listContainer]-10-|";
NSArray *constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:NSLayoutFormatAlignAllLeft metrics:nil views:viewsDictionary];
[self.contentView addConstraints:constraintsArray];
format = @"|-10-[questionText]-10-|";
constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:NSLayoutFormatAlignAllLeft metrics:nil views:viewsDictionary];
[self.contentView addConstraints:constraintsArray];
format = @"|-10-[listContainer]-10-|";
constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:NSLayoutFormatAlignAllLeft metrics:nil views:viewsDictionary];
[self.contentView addConstraints:constraintsArray];
ToggleButton *prevCheckbox;
ToggleButton *checkbox;
for (AssessmentAnswer *answer in self.field.answers)
{
checkbox = [[ToggleButton alloc] initWithText:answer.text ofType:ToggleButtonTypeCheckbox];
[checkbox setTranslatesAutoresizingMaskIntoConstraints:NO];
[listContainer addSubview:checkbox];
viewsDictionary = NSDictionaryOfVariableBindings(checkbox);
format = @"|-10-[checkbox]-10-|";
constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:NSLayoutFormatAlignAllCenterY metrics:nil views:viewsDictionary];
[listContainer addConstraints:constraintsArray];
if (prevCheckbox)
{
// This is not the first item
[listContainer addConstraint:[NSLayoutConstraint constraintWithItem:checkbox attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:prevCheckbox attribute:NSLayoutAttributeBottom multiplier:1.0 constant:20.0]];
}
else
{
// This is the first item
[listContainer addConstraint:[NSLayoutConstraint constraintWithItem:checkbox attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:listContainer attribute:NSLayoutAttributeTop multiplier:1.0 constant:10.0]];
}
prevCheckbox = checkbox;
}
if (checkbox)
{
// This is the last checkbox
[listContainer addConstraint:[NSLayoutConstraint constraintWithItem:listContainer attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:checkbox attribute:NSLayoutAttributeBottom multiplier:1.0 constant:10.0]];
}
在这种情况下，self.field.answers中只有一个项目。字体与下面使用的值相同。
以下是单元格高度的代码：
UIFont *font = [UIFont fontWithName:@"Helvetica" size:14.0];
//Find height of question text
CGFloat questionTextHeight = [field.questionText sizeWithFont:font constrainedToSize:CGSizeMake(width - (2 * PAD_X), CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping].height;
//Find height of each row
CGFloat listHeight = 0.0;
for (AssessmentAnswer *answer in field.answers)
{
listHeight += MAX([answer.text sizeWithFont:font constrainedToSize:CGSizeMake(width - 43.0 - [ToggleButton getImageWidth], CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping].height, [ToggleButton getImageHeight]) + 20.0;
}
// Question text height + list height + spacers
return questionTextHeight + listHeight + 30.0;
以下是创建ToggleButton内部的代码，它是一个UIButton：
for (UIView *subview in self.subviews)
{
[subview removeFromSuperview];
}
// Add the toggle button image
self.toggleImgView = [[UIImageView alloc] init];
[self.toggleImgView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self addSubview:self.toggleImgView];
// Add the label
self.toggleLabel = [[UILabel alloc] init];
self.toggleLabel.font = [UIFont fontWithName:@"Helvetica" size:14.0f];
self.toggleLabel.numberOfLines = 0;
self.toggleLabel.adjustsFontSizeToFitWidth = NO;
self.toggleLabel.lineBreakMode = NSLineBreakByWordWrapping;
self.toggleLabel.backgroundColor = [UIColor clearColor];
[self.toggleLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
[self addSubview:self.toggleLabel];
// Get the views dictionary
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(_toggleImgView, _toggleLabel);
//Create the constraints using the visual language format
NSString *format = [NSString stringWithFormat:@"|-0-[_toggleImgView(%f)]-3-[_toggleLabel]-0-|", IMAGE_WIDTH];
NSArray *constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:nil metrics:nil views:viewsDictionary];
[self addConstraints:constraintsArray];
viewsDictionary = NSDictionaryOfVariableBindings(_toggleLabel);
format = [NSString stringWithFormat:@"V:|-0-[_toggleLabel(>=%f)]-0-|", IMAGE_HEIGHT];
constraintsArray = [NSLayoutConstraint constraintsWithVisualFormat:format options:NSLayoutFormatAlignAllLeft metrics:nil views:viewsDictionary];
[self addConstraints:constraintsArray];
[self addConstraint:[NSLayoutConstraint constraintWithItem:self.toggleImgView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.toggleImgView attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];
[self addConstraint:[NSLayoutConstraint constraintWithItem:self.toggleImgView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.toggleLabel attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
以下是我得到的异常读数：
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)
(
"<NSLayoutConstraint:0x1f28c4f0 V:[UILabel:0x1f288f10(>=27)]>",
"<NSLayoutConstraint:0x1f291460 V:[ToggleButton:0x1f068e50]-(10)-| (Names: '|':UIView:0x1f0182a0 )>",
"<NSLayoutConstraint:0x1f293830 V:[UILabel:0x1f288f10]-(0)-| (Names: '|':ToggleButton:0x1f068e50 )>",
"<NSLayoutConstraint:0x1f28b480 V:|-(10)-[UILabel:0x1f062890] (Names: '|':UITableViewCellContentView:0x1f1c23d0 )>",
"<NSLayoutConstraint:0x1f29b070 V:|-(10)-[ToggleButton:0x1f068e50] (Names: '|':UIView:0x1f0182a0 )>",
"<NSLayoutConstraint:0x1f289810 V:[UIView:0x1f0182a0]-(10)-| (Names: '|':UITableViewCellContentView:0x1f1c23d0 )>",
"<NSLayoutConstraint:0x1f292eb0 V:|-(0)-[UILabel:0x1f288f10] (Names: '|':ToggleButton:0x1f068e50 )>",
"<NSLayoutConstraint:0x1f28dc90 V:[UILabel:0x1f062890]-(10)-[UIView:0x1f0182a0]>",
"<NSAutoresizingMaskLayoutConstraint:0x1f1e5ed0 h=--& v=--& V:[UITableViewCellContentView:0x1f1c23d0(60)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x1f293830 V:[UILabel:0x1f288f10]-(0)-| (Names: '|':ToggleButton:0x1f068e50 )>
Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
我不明白为什么我得到了例外，因为所有的高度加起来。这种情况与其他一些细胞类型一起发生，因此任何见解都会有所帮助。
答案 0 :(得分：1)
错误消息非常清楚地告诉您它不能满足要求ToggleButton中的UILabel高度大于或等于27的约束。据推测，在布局过程中的某些时候，没有足够的空间来保持你已经规定的其他垂直间距规则。
有趣的是，我实际上并没有看到关于代码中UILabel高度的约束;也许你在笔尖设置它？如果是这样，请尝试降低其优先级，或者设置一个插座并在笔尖加载后将其删除。从这里开始有点神秘，因为你没有解释ToggleButton是什么。但它肯定似乎里面有一个UILabel，并且UILabel肯定似乎有高度不平等，这是造成麻烦的原因。