问题描述

我正在尝试将自动布局合并到我的 UITableViewHeaderFooterView 子类中.该类非常基础，只有两个标签.这是完整的子类:

I am trying to incorporate auto layout into my UITableViewHeaderFooterView subclass. The class is pretty basic, just two labels. This is the complete subclass:

@implementation MBTableDetailStyleFooterView

static void MBTableDetailStyleFooterViewCommonSetup(MBTableDetailStyleFooterView *_self) {
    UILabel *rightLabel = [[UILabel alloc] init];
    _self.rightLabel = rightLabel;
    rightLabel.translatesAutoresizingMaskIntoConstraints = NO;
    [_self.contentView addSubview:rightLabel];

    UILabel *leftLabel = [[UILabel alloc] init];
    _self.leftLabel = leftLabel;
    leftLabel.translatesAutoresizingMaskIntoConstraints = NO;
    [_self.contentView addSubview:leftLabel];

    NSDictionary *views = NSDictionaryOfVariableBindings(rightLabel, leftLabel);

    NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"|-10-[leftLabel]-(>=10)-[rightLabel]-10-|" options:0 metrics:nil views:views];
    [_self.contentView addConstraints:horizontalConstraints];

    // center views vertically in super view
    NSLayoutConstraint *leftCenterYConstraint = [NSLayoutConstraint constraintWithItem:leftLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_self.contentView attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];
    [_self.contentView addConstraint:leftCenterYConstraint];
    NSLayoutConstraint *rightCenterYConstraint = [NSLayoutConstraint constraintWithItem:rightLabel attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_self.contentView attribute:NSLayoutAttributeCenterY multiplier:1 constant:0];
    [_self.contentView addConstraint:rightCenterYConstraint];

    // same height for both labels
    NSLayoutConstraint *sameHeightConstraint = [NSLayoutConstraint constraintWithItem:leftLabel attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:rightLabel attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
    [_self.contentView addConstraint:sameHeightConstraint];
}

+ (BOOL)requiresConstraintBasedLayout {
    return YES;
}

- (id)initWithReuseIdentifier:(NSString *)reuseIdentifier {
    self = [super initWithReuseIdentifier:reuseIdentifier];
    MBTableDetailStyleFooterViewCommonSetup(self);
    return self;
}

@end

该类用作具有 2 个部分的 tableView 的第一部分的页脚.第一部分包含动态项目.第二部分只有一行，用于向第一部分添加新项目.

This class is used as a footer in the first section in a tableView with 2 sections. The first section contains dynamic items. The second section has only one row, which is used to add new items to the first section.

如果第一部分中没有项目，我会隐藏 footerView.因此，当我添加第一个新项目时，我必须重新加载该部分，以便显示 footerView.完成这一切的代码如下所示:

If there are no items in the first section I hide the footerView. So when I add the first new item I have to reload the section so the footerView appears. The code that does all this looks like this:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    [tableView deselectRowAtIndexPath:indexPath animated:YES];
    if (indexPath.section == 1) {
        BOOL sectionNeedsReload = ([self.data count] == 0); // reload section when no data (and therefor no footer) was present before the add
        [self.data addObject:[NSDate date]];
        NSIndexPath *newIndexPath = [NSIndexPath indexPathForRow:[self.data count]-1 inSection:0];
        if (sectionNeedsReload) {
            [self.tableView reloadSections:[NSIndexSet indexSetWithIndex:0] withRowAnimation:UITableViewRowAnimationAutomatic];
        }
        else {
            [self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
        }
        [self configureFooter:(MBTableDetailStyleFooterView *)[tableView footerViewForSection:0] forSection:0];
    }
}

- (void)configureFooter:(MBTableDetailStyleFooterView *)footer forSection:(NSInteger)section {
    footer.leftLabel.text = @"Total";
    footer.rightLabel.text = [NSString stringWithFormat:@"%d", [self.data count]];
}

- (UIView *)tableView:(UITableView *)tableView viewForFooterInSection:(NSInteger)section {
    MBTableDetailStyleFooterView *footer = nil;
    if (section == 0 && [self.data count]) {
        footer = [tableView dequeueReusableHeaderFooterViewWithIdentifier:@"Footer"];
        [self configureFooter:footer forSection:section];
    }
    return footer;
}

- (CGFloat)tableView:(UITableView *)tableView heightForFooterInSection:(NSInteger)section {
    CGFloat height = 0;
    if (section == 0 && [self.data count]) {
        height = 20.0f;
    }
    return height;
}

没什么特别的.但是，只要在我的 tableView 上调用 reloadSections:withRowAnimations: 就会引发异常，因为它无法同时满足约束".

Nothing really fancy. However, as soon as reloadSections:withRowAnimations: is called on my tableView it throws an exception because it is "Unable to simultaneously satisfy constraints.".

tableView 在某处向我的页脚添加了翻译后的自动调整大小掩码约束.

Somewhere the tableView added a translated auto resizing mask constraint to my footer.

(
    "<NSLayoutConstraint:0x718a1f0 H:[UILabel:0x7189130]-(10)-|   (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )>",
    "<NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(>=10)-[UILabel:0x7189130]>",
    "<NSLayoutConstraint:0x718a0a0 H:|-(10)-[UILabel:0x71892c0]   (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )>",
    "<NSAutoresizingMaskLayoutConstraint:0x7591ab0 h=--& v=--& H:[_UITableViewHeaderFooterContentView:0x7188df0(0)]>"
)

当我将 reloadSections:withRowAnimations: 替换为对 reloadData 的调用时，不会添加自动调整大小的掩码约束，并且一切正常.

When I replace reloadSections:withRowAnimations: with a call to reloadData no autoresizing mask constraint is added and everything works fine.

有趣的是，异常告诉我它试图打破约束 <NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(>=10)-[UILabel:0x7189130]>

(
    "<NSLayoutConstraint:0x718a0a0 H:|-(10)-[UILabel:0x71892c0]   (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )>",
    "<NSLayoutConstraint:0x7189e30 H:[UILabel:0x71892c0]-(>=10)-[UILabel:0x7189130]>",
    "<NSLayoutConstraint:0x718a1f0 H:[UILabel:0x7189130]-(10)-|   (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )>",
    "<NSLayoutConstraint:0x718a3f0 UILabel:0x71892c0.centerY == _UITableViewHeaderFooterContentView:0x7188df0.centerY>",
    "<NSLayoutConstraint:0x718a430 UILabel:0x7189130.centerY == _UITableViewHeaderFooterContentView:0x7188df0.centerY>",
    "<NSLayoutConstraint:0x718a4b0 UILabel:0x71892c0.height == UILabel:0x7189130.height>"
)

- (void)setFrame:(CGRect)frame {
    if (frame.size.width == 0) {
        return;
    }
    
    [super setFrame:frame];
}