Question

我正在尝试在每个自定义单元格（继承自NSLayoutConstraint）中设置UITableViewCell，而不是在UIViewController中指定它们，以避免因为每个自定义约束而使其混乱细胞类型。

问题在于我无法找到单元生命周期的适当部分来创建布局约束（我尝试layoutSubviews()和awakeFromNib()），但它们都在单元的生命周期中被调用得太早，当其superview尚未定义时 - 会导致此错误：

约束必须包含第一个布局项

由于UITableViewCell没有像viewDidLoad()那样的UIViewController方法，如何在单元格中定义布局约束呢？

layoutSubviews()自定义UITableViewCell：

- (void) layoutSubviews {
    self.translatesAutoresizingMaskIntoConstraints = false;
    [[NSLayoutConstraint constraintWithItem: self.attributeNameLabel
                                  attribute: NSLayoutAttributeLeading
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.contentView
                                  attribute: NSLayoutAttributeLeading
                                 multiplier: 1
                                   constant: 3] setActive:true];
    [[NSLayoutConstraint constraintWithItem: self.attributeNameLabel
                                  attribute: NSLayoutAttributeTop
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.contentView
                                  attribute: NSLayoutAttributeTop
                                 multiplier: 1
                                   constant: 3] setActive:true];
    [[NSLayoutConstraint constraintWithItem: self.attributeNameLabel
                                  attribute: NSLayoutAttributeRight
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.contentView
                                  attribute: NSLayoutAttributeRight
                                 multiplier: 1
                                   constant: 3] setActive:true];
    [[NSLayoutConstraint constraintWithItem: self.attributeNameLabel
                                  attribute: NSLayoutAttributeBottom
                                  relatedBy: NSLayoutRelationEqual
                                     toItem: self.contentView
                                  attribute: NSLayoutAttributeBottom
                                 multiplier: 1
                                   constant: 3] setActive:true];   
}

UIViewController中的初始化示例：

- (UITableViewCell *)tableView:(UITableView *)view cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell;

    if (indexPath.row % 2 == 0) {
        cell = [[CustomCell1 alloc] init];
    } else if (indexPath.row % 2 == 1) {
        cell = [[CustomCell2 alloc] init];
    } else if (...) {
        ...
    }
    return cell;
}

Answer 1

尝试制作

 self.attributeNameLabel.translatesAutoresizingMaskIntoConstraints = NO;

对于每个标签而不是contentView

转换它们就像它对我有用

这样做

  - (void)awakeFromNib {
// Initialization code



[super awakeFromNib];


UILabel*ddd = [UILabel new];

ddd.text = @"adsbcujklasdcbaksci";

ddd.translatesAutoresizingMaskIntoConstraints = NO ;

[self.contentView addSubview:ddd];

 NSLayoutConstraint*ss1 =  [NSLayoutConstraint constraintWithItem: ddd
                              attribute: NSLayoutAttributeCenterX
                              relatedBy: NSLayoutRelationEqual
                                 toItem: self.contentView
                              attribute: NSLayoutAttributeCenterX
                             multiplier: 1 constant: 3] ;
NSLayoutConstraint*ss2 =  [NSLayoutConstraint constraintWithItem: ddd
                              attribute: NSLayoutAttributeCenterY
                              relatedBy: NSLayoutRelationEqual
                                 toItem: self.contentView
                              attribute: NSLayoutAttributeCenterY
                             multiplier: 1   constant: 3]  ;

 [self.contentView addConstraints:@[ss1,ss2]];



 [self layoutSubviews];

 [self layoutIfNeeded];



}

UITableViewCell的NSLayoutConstraint：约束必须包含第一个布局项

1 个答案: