我试图将自动布局合并到我的UITableViewHeaderFooterView子类中.该课程是非常基本的,只有两个标签.这是完整的子类：
@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
这个类用作tableView中的第一部分的页脚,具有2个部分.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.
如果第一部分没有项目,我隐藏了脚注视图.所以当我添加第一个新项目时,我必须重新加载该部分,以便footerView出现.所有这些代码看起来像这样：
- (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;
}
没什么好想的但是,只要reloadSections：withRowAnimations：在我的tableView上被调用,它会抛出异常,因为它是“无法同时满足约束”.
在某处,tableView将翻译的自动调整大小的掩码约束添加到我的页脚.
(
"<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)]>"
)
当我替换reloadSections：withRowAnimations：调用reloadData不添加自动调整掩码约束,一切正常.
有趣的是,异常告诉我,它试图中断约束< NSLayoutConstraint：0x7189e30 H：[UILabel：0x71892c0] - (> = 10) – [UILabel：0x7189130]>
但是当我在对configureFooter的后续调用中记录约束：forSection：该约束仍然存在,但是自动调整大小掩码约束已经消失
这些约束正是我所设定的.
(
"<NSLayoutConstraint:0x718a0a0 H:|-(10)-[UILabel:0x71892c0] (Names: '|':_UITableViewHeaderFooterContentView:0x7188df0 )>","<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>"
)
这个自动调整大小面膜约束来自哪里？哪里去
我错过了什么吗？我第一次看汽车布局就像一个星期前,所以这是完全可能的.
解决方法
我有一个类似的问题,只有一个额外的标签在contentView.尝试插入
static void MBTableDetailStyleFooterViewCommonSetup(MBTableDetailStyleFooterView *_self) {
_self.contentView.translatesAutoresizingMaskIntoConstraints = NO
[...]
}
在您的MBTableDetailStyleFooterViewCommonSetup函数的第一行.对于我来说,这与reloadSections结合使用：withRowAnimations :.
更新：
我还为contentView添加了一个新的约束来使用所有宽度：
NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[contentView]|"
options:0
metrics:nil
views:@{@"contentView" : _self.contentView}];
[_self.contentView.superview addConstraints:horizontalConstraints];
