ios - 获取自动布局、NSAutoLayout、objective C 的警告

Question

我的目标：将指示器（垂直和水平）居中到视图中的按钮

我正在做的是：

[self.logInButton addConstraint:[NSLayoutConstraint constraintWithItem:spinner1
                                                             attribute:NSLayoutAttributeCenterY
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:self.logInButton
                                                             attribute:NSLayoutAttributeCenterY
                                                            multiplier:1.0
                                                              constant:0]];
[self.logInButton addConstraint:[NSLayoutConstraint constraintWithItem:spinner1
                                                             attribute:NSLayoutAttributeCenterX
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:self.logInButton
                                                             attribute:NSLayoutAttributeCenterX
                                                            multiplier:1.0
                                                              constant:0]];
self.logInButton addSubView:spinner

但是，我在下面收到警告

The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x17e19390 UIActivityIndicatorView:0x17d035d0.centerY == UIButton:0x17df4430.centerY>
    When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView _viewHierarchyUnpreparedForConstraint:] to debug.
2013-06-12 17:37:19.610 FlipGive[366:60b] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x17e19810 UIActivityIndicatorView:0x17d035d0.centerX == UIButton:0x17df4430.centerX>
    When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView _viewHierarchyUnpreparedForConstraint:] to debug.

有谁知道我在这里做错了什么？请帮忙

欢迎所有评论在这里。谢谢

Answer 1

您需要在添加约束之前添加视图。

先放这个，然后添加约束

self.logInButton addSubView:spinner