ios - 自动布局问题

我正在开发一个使用自动布局的应用程序。我正在执行以下步骤:

步骤1:在viewDidLoad中创建一个按钮

[super viewDidLoad];

self.view.translatesAutoresizingMaskIntoConstraints = NO;

_button1 = [UIButton buttonWithType:UIButtonTypeRoundedRect];
_button1.translatesAutoresizingMaskIntoConstraints = NO;
[_button1 setTitle:@"B" forState:UIControlStateNormal];
[self.view addSubview:_button1];

步骤2:在updateViewConstraints方法中实现约束

[super updateViewConstraints];

[self.view removeConstraints:self.view.constraints];

if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
{
    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0f constant:100.0f];
    [self.view addConstraint:constraint];

    NSLayoutConstraint *constraint1 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0f constant:-100.0f];
    [self.view addConstraint:constraint1];

    NSLayoutConstraint *constraint2 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0f constant:200.0f];
    [self.view addConstraint:constraint2];

    NSLayoutConstraint *constraint3 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0f constant:-100.0f];
    [self.view addConstraint:constraint3];


    _button1.backgroundColor = [UIColor redColor];
} else{
    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0f constant:200.0f];
    [self.view addConstraint:constraint];

    NSLayoutConstraint *constraint1 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0f constant:-200];
    [self.view addConstraint:constraint1];

    NSLayoutConstraint *constraint2 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0f constant:50.0f];
    [self.view addConstraint:constraint2];

    NSLayoutConstraint *constraint3 = [NSLayoutConstraint constraintWithItem:_button1 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0f constant:-50.0f];
    [self.view addConstraint:constraint3];

    _button1.backgroundColor = [UIColor blueColor];
}

但是当我切换设备方向时，控制台将打印以下内容:

无法同时满足约束条件。大概至少一个
以下列表中的约束之一是您不想要的约束。尝试
这:(1)查看每个约束，并尝试找出哪个约束
没想到(2)找到添加了不必要约束的代码或
约束并修复它。 (注意:如果您看到
您不了解的NSAutoresizingMaskLayoutConstraints，请参阅
到UIView属性的文档
平移AutoresizingMaskIntoConstraints)(
“UIView:0x8a461c0(名称:'|':UIWindow:0x8a42970)>”，
“”，
“”，
“UIButton:0x8a45ea0(名称:'|':UIView:0x8a461c0)>”，
“”)

将尝试通过打破约束来恢复


中断objc_exception_throw以在调试器中捕获此错误。的
UIView上的UIConstraintBasedLayoutDebugging类别中的方法
列出的内容也可能会有帮助。

谁能告诉我这种布局有什么问题吗？

最佳答案

问题是您在仍然对按钮有约束的情况下在[super updateViewConstraints]中调用updateViewConstraints。因此，当您从横向过渡到纵向时，您仍然具有横向按钮约束(纵向无法满足)，但是要求主视图更新其(人像)约束。如果在删除所有现有的按钮约束后将调用移至[super updateViewConstraints]的任何位置，则您的状态应良好。

几个方面:

如果使用情节提要/ NIBS，则应删除显示以下内容的行:

self.view.translatesAutoresizingMaskIntoConstraints = NO;

但请保留以下内容:

_button1.translatesAutoresizingMaskIntoConstraints = NO;

我会警惕大规模删除所有约束的情况。我通常会保留要删除的约束数组，这样一来，我可以轻松删除仅需要删除并将要重构的约束。在您的情况下，删除所有内容可能没问题，但是随着您向视图中添加越来越多的约束，跟踪要删除和重建的对象可能更容易:

@property (nonatomic, strong) NSArray *verticalConstraints;
@property (nonatomic, strong) NSArray *horizontalConstraints;

我可能建议使用VFL，这更加简洁:

- (void)updateViewConstraints
{
    if (self.horizontalConstraints)
        [self.view removeConstraints:self.horizontalConstraints];

    if (self.verticalConstraints)
        [self.view removeConstraints:self.verticalConstraints];

    [super updateViewConstraints];

    NSDictionary *views   = NSDictionaryOfVariableBindings(_button1);
    NSDictionary *metrics = nil;

    if (UIInterfaceOrientationIsPortrait([UIApplication sharedApplication].statusBarOrientation))
    {
        metrics = @{@"left"   : @100,
                    @"right"  : @100,
                    @"top"    : @200,
                    @"bottom" : @100};

        _button1.backgroundColor = [UIColor redColor];
    } else{
        metrics = @{@"left"   : @200,
                    @"right"  : @200,
                    @"top"    : @50,
                    @"bottom" : @50};

        _button1.backgroundColor = [UIColor blueColor];
    }

    self.horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-(left)-[_button1]-(right)-|" options:0 metrics:metrics views:views];
    self.verticalConstraints   = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(top)-[_button1]-(bottom)-|" options:0 metrics:metrics views:views];
    [self.view addConstraints:self.horizontalConstraints];
    [self.view addConstraints:self.verticalConstraints];
}