覆盖updateViewConstraints方法UIViewController为特定情况提供布局约束。这样，布局总是根据实际情况来设置正确的方式。确保它们与故事板中创建的约束一起形成完整的约束。可以使用IB设置一般约束，并将要更改的对象标记为在运行时删除。

​

​

我使用以下实现为每个方向提供了一组不同的约束：

-(void)updateViewConstraints {
    [super updateViewConstraints];

    // constraints for portrait orientation
    // use a property to change a constraint's constant and/or create constraints programmatically, e.g.:
    if (!self.layoutConstraintsPortrait) {
        UIView *image1 = self.image1;
        UIView *image2 = self.image2;
        self.layoutConstraintsPortrait = [[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[image1]-[image2]-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(image1, image2)] mutableCopy];
        [self.layoutConstraintsPortrait addObject:[NSLayoutConstraint constraintWithItem:image1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem: image1.superview attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
        [self.layoutConstraintsPortrait addObject:[NSLayoutConstraint constraintWithItem:image2 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:image2.superview attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
    }

    // constraints for landscape orientation
    // make sure they don't conflict with and complement the existing constraints
    if (!self.layoutConstraintsLandscape) {
        UIView *image1 = self.image1;
        UIView *image2 = self.image2;
        self.layoutConstraintsLandscape = [[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[image1]-[image2]-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(image1, image2)] mutableCopy];
        [self.layoutConstraintsLandscape addObject:[NSLayoutConstraint constraintWithItem:image1 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:image1.superview attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
        [self.layoutConstraintsLandscape addObject:[NSLayoutConstraint constraintWithItem:image2 attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem: image2.superview attribute:NSLayoutAttributeCenterY multiplier:1 constant:0]];
    }

    BOOL isPortrait = UIInterfaceOrientationIsPortrait(self.interfaceOrientation);
    [self.view removeConstraints:isPortrait ? self.layoutConstraintsLandscape : self.layoutConstraintsPortrait];
    [self.view addConstraints:isPortrait ? self.layoutConstraintsPortrait : self.layoutConstraintsLandscape];        
}

现在，只要情况发生变化，就只需触发约束更新即可。覆盖willAnimateRotationToInterfaceOrientation:duration:若要对方向更改进行约束更新，请执行以下操作：

- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
    [super willAnimateRotationToInterfaceOrientation:toInterfaceOrientation duration:duration];

    [self.view setNeedsUpdateConstraints];

}

为了避免狗血的故事板警告，我把所有的一组放在999的优先级上，这样它在任何地方都不会显示红色。

然后我将所有约束添加到出口集合中：

@property (strong, nonatomic) IBOutletCollection(NSLayoutConstraint) NSArray *portraitConstraints;
@property (strong, nonatomic) IBOutletCollection(NSLayoutConstraint) NSArray *landscapeConstraints;

最后，我执行我的ViewControllers的viewWillLayout method：

- (void) viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    for (NSLayoutConstraint *constraint in self.portraitConstraints) {
        constraint.active = (UIApplication.sharedApplication.statusBarOrientation == UIDeviceOrientationPortrait);
    }
    for (NSLayoutConstraint *constraint in self.landscapeConstraints) {
        constraint.active = (UIApplication.sharedApplication.statusBarOrientation != UIDeviceOrientationPortrait);
    }
}