Question

我试图找到最简洁的方法来调整我的UITableView的tableHeaderView的高度，它本身只是一个带有多行标签的视图。似乎autolayout应该能够很容易地计算出高度。

我像这样创建标签：

DDInsetLabelView *header = [[DDInsetLabelView alloc] initWithFrame:CGRectZero];
header.insets = UIEdgeInsetsMake(10.f, 10.f, 10.f, 10.f);
header.label.text = [NSString stringWithFormat:@"%@\n%@", self.categoryTitle, self.subcategoryTitle];
header.label.numberOfLines = 0;
header.label.textAlignment = NSTextAlignmentCenter;
self.tableView.tableHeaderView = header;

在标签类中，我处理这样的布局：

- (void)updateConstraints {
    [super updateConstraints];

    NSDictionary *metrics = @{@"t": @(self.insets.top), @"l": @(self.insets.left),
                              @"b": @(self.insets.bottom), @"r": @(self.insets.right)};
    NSDictionary *views = NSDictionaryOfVariableBindings(_label);
    self.label.translatesAutoresizingMaskIntoConstraints = NO;
    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(t)-[_label]-(b)-|" options:0 metrics:metrics views:views]];
    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-(l)-[_label]-(r)-|" options:0 metrics:metrics views:views]];
}

- (void)layoutSubviews {
    [super layoutSubviews];
    self.label.preferredMaxLayoutWidth = self.label.frame.size.width;
    [super layoutSubviews];
}

现在，这是我如何计算控制器中标题视图的高度：

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    UIView *header = self.tableView.tableHeaderView;
    NSLayoutConstraint *headerWidthConstraint = [NSLayoutConstraint
                                                 constraintWithItem:header attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual
                                                 toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0f constant:header.frame.size.width];
    [header addConstraint:headerWidthConstraint];
    CGFloat height = [header systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
    [header removeConstraint:headerWidthConstraint];

    header.frame = CGRectMake(0, 0, header.frame.size.width, height);
    header.translatesAutoresizingMaskIntoConstraints = YES;
    self.tableView.tableHeaderView = header;
}

看起来这在视觉上很好用，但我在控制台中一直收到以下错误：

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:0x7fb2e5bb7540 'UIView-Encapsulated-Layout-Height' V:[DDInsetLabelView:0x7fb2e5b53250(0)]>",
    "<NSLayoutConstraint:0x7fb2e5bb84b0 V:|-(10)-[UILabel:0x7fb2e5b65200'Custom Box\nCustomize with...']   (Names: '|':DDInsetLabelView:0x7fb2e5b53250 )>",
    "<NSLayoutConstraint:0x7fb2e5bb8500 V:[UILabel:0x7fb2e5b65200'Custom Box\nCustomize with...']-(10)-|   (Names: '|':DDInsetLabelView:0x7fb2e5b53250 )>"
)

我假设UIView-Encapsulated-Layout-Height表示标头的一些内部计算的高度值。如何在使用autolayout计算标题的高度时避免此警告？

Answer 1

尝试删除该行... header.translatesAutoresizingMaskIntoConstraints = YES;

另外，在创建标题时添加[header setTranslatesAutoresizingMaskIntoConstraints:NO]

UIView-Encapsulated-Layout-Height：tableHeaderView中的约束无效

1 个答案: