视图层次结构没有为约束做好准备？

Posted 2023-03-15

【中文标题】视图层次结构没有为约束做好准备？

【英文标题】：The view hierarchy is not prepared for the constraint?

【发布时间】：2015-08-12 19:51:15

【问题描述】：

我收到以下错误，即使我在添加按钮和应用约束之前设置了表格视图页脚。在-viewDidLoad 和-viewDidAppear 中设置和页脚视图后，我尝试调用以下方法。我似乎无法隔离问题。

视图层次结构没有为约束做好准备： 当添加到 视图，约束的项目必须是该视图的后代（或 查看自己）。如果需要解决约束，这将崩溃 在组装视图层次结构之前。打破 - [UIView _viewHierarchyUnpreparedForConstraint:] 进行调试。

2015-08-12 15:43:05.086 myApp[2293:299005] 未准备好查看层次结构 为约束。约束：容器层次结构：> | > 在容器层次结构中找不到视图： > 该视图的超级视图：;层 = ;内容偏移：0, 0;内容大小：800, 75>

这是我用来添加按钮和应用约束的代码：

- (void)addButtonContraints
//Create button
    _nextQuestionButton = [UIButton buttonWithType:UIButtonTypeSystem];
    [_nextQuestionButton addTarget:self action:@selector(nextQuestion) forControlEvents:UIControlEventTouchUpInside];
    //_nextQuestionButton.frame = CGRectMake(0, 0, 200,40);
    [_nextQuestionButton setTitle:@"Next Question" forState:UIControlStateNormal];
    [_nextQuestionButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    _nextQuestionButton.backgroundColor = [UIColor whiteColor];
    _nextQuestionButton.titleLabel.attributedText = [[NSAttributedString alloc] initWithString:@"Next Question"
                                                                                    attributes:@NSForegroundColorAttributeName:[UIColor blackColor], NSFontAttributeName:[UIFont fontWithName:@"HelveticaNeue-Bold" size:18.0f]];

    //Add shadow to button
    UIBezierPath *shadowPath = [UIBezierPath bezierPathWithRect:_nextQuestionButton.bounds];
    _nextQuestionButton.layer.masksToBounds = NO;
    _nextQuestionButton.layer.shadowColor = [UIColor blackColor].CGColor;
    _nextQuestionButton.layer.shadowOffset = CGSizeMake(0.0f, 5.0f);
    _nextQuestionButton.layer.shadowOpacity = 0.25f;
    _nextQuestionButton.layer.shadowPath = shadowPath.CGPath;

    [_nextQuestionButton setTranslatesAutoresizingMaskIntoConstraints:NO];


    [self.quizTableView.tableFooterView addSubview:_nextQuestionButton];



    //Add contraints to button

    NSDictionary *dict = NSDictionaryOfVariableBindings(_nextQuestionButton);

    //width
    [_nextQuestionButton addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[_nextQuestionButton(200)]"
                                                                                options:0x00
                                                                                metrics:nil
                                                                                  views:dict]];
    //height
    [_nextQuestionButton addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_nextQuestionButton(40)]"
                                                                                options:0x00
                                                                                metrics:nil
                                                                                  views:dict]];
    //right
    [_nextQuestionButton addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"[_nextQuestionButton]-40-|"
                                                                                options:0x00
                                                                                metrics:nil
                                                                                  views:dict]];
    //top
    [_nextQuestionButton addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[_nextQuestionButton]"
                                                                                options:0x00
                                                                                metrics:nil
                                                                                  views:dict]];
    _nextQuestionButton.hidden = YES;

【参考方案1】：

您应该将最后两个约束添加到 self.quizTableView.tableFooterView，而不是 _nextQuestionButton。