ios - 为什么这不足以添加一个 View 以使用自动布局占据所有屏幕？

Question

我不明白为什么这对添加 subview 不起作用。

UIView *orangeView = [[UIView alloc] init];
orangeView.translatesAutoresizingMaskIntoConstraints = NO;
orangeView.backgroundColor = [UIColor orangeColor];

[self.view addSubview:orangeView];

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0]];

我没有收到任何错误或警告，但 View 没有显示。

Answer 1

您正在向 self.view 添加约束，使 self.view 与 self.view 具有相同的尺寸。添加约束时永远不要使用 orangeView。

将您的代码更改为:

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:orangeView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0.0]];