ios - 正确的子类化和UITableViewHeaderFooterView的自动布局

这是我在UITableViewHeaderFooterView视图中设置内容的方法。

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
    [self.contentView addSubview:self.createHeader];
}
return self;
}

- (UIView *)createHeader
{
  UIView *headerContainer = [[UIView alloc] init];
  headerContainer.backgroundColor = [UIColor blackColor];
  UILabel *label = [[UILabel alloc] initWithFrame:CGRectZero];
  label.translatesAutoresizingMaskIntoConstraints = NO;
  label.text = @"titlename";

  [headerContainer addSubview:label];

  NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:label
                                                                   attribute:NSLayoutAttributeLeading
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:headerContainer
                                                              attribute:NSLayoutAttributeLeft
                                                             multiplier:1.f constant:16.f];
[headerContainer addConstraint:constraint];

constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeTrailing
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:headerContainer
                                          attribute:NSLayoutAttributeRight
                                         multiplier:1.f constant:-16.f];
[headerContainer addConstraint:constraint];

constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeTop
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:headerContainer
                                          attribute:NSLayoutAttributeTop
                                         multiplier:1.f constant:0.f];
[headerContainer addConstraint:constraint];

constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeBottom
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:headerContainer
                                          attribute:NSLayoutAttributeBottom
                                         multiplier:1.f constant:0.f];
[headerContainer addConstraint:constraint];

return headerContainer;
}

我收到此自动布局错误:

 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:0xd4bd7e0 UILabel:0x17254980.leading == UIView:0x172547d0.left + 16>",
"<NSLayoutConstraint:0xd4bd810 UILabel:0x17254980.trailing == UIView:0x172547d0.right - 16>",
"<NSAutoresizingMaskLayoutConstraint:0xd402510 h=--& v=--& H:[UIView:0x172547d0(0)]>"
)

Will attempt to recover by breaking constraint
<NSLayoutConstraint:0xd4bd810 UILabel:0x17254980.trailing == UIView:0x172547d0.right - 16>

最佳答案

错误的线索就在那里:translatesAutoresizingMaskIntoConstraints。

我会说您需要将以下行添加到createHeader方法中:
headerContainer.translatesAutoresizingMaskIntoConstraints = NO;
这是第二个想法。看起来您想将标签居中在headerContainer中，对吗？代替:

NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:label
                                                                   attribute:NSLayoutAttributeLeading
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:headerContainer
                                                              attribute:NSLayoutAttributeLeft
                                                             multiplier:1.f constant:16.f];
[headerContainer addConstraint:constraint];

constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeTrailing
                                          relatedBy: NSLayoutRelationLessThanOrEqual
                                             toItem:headerContainer
                                          attribute:NSLayoutAttributeRight
                                         multiplier:1.f constant:-16.f];
[headerContainer addConstraint:constraint];

尝试:

NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:label
                                                                   attribute:NSLayoutAttributeLeading
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:headerContainer
                                                              attribute:NSLayoutAttributeLeft
                                                             multiplier:1.f constant:16.f];
[headerContainer addConstraint:constraint];

constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeTrailing
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:label
                                          attribute:NSLayoutAttributeLeading
                                         multiplier:1.f constant:0];
[headerContainer addConstraint:constraint];