ios - WKWebView 约束不起作用

Question

我只是希望 WKWebView 固定到 self.view 的所有侧面，这样无论旋转它总是尽可能地拉伸(stretch)。使用以下代码，它将填充 View 以适应初始旋转，但旋转后，它会全部消失:

-(void)viewWillAppear:(BOOL)animated {
    [super viewDidLoad];
    self.title = @"Worship Slides";

    self.productURL = @"http://www.316apps.com/Fritch/worship.key";

    NSURL *url = [NSURL URLWithString:self.productURL];
    NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:60.0];

    _theWorship = [[WKWebView alloc] initWithFrame:self.view.frame];
    [_theWorship setTranslatesAutoresizingMaskIntoConstraints:NO];

    [_theWorship loadRequest:request];
    _theWorship.frame = CGRectMake(0, 0, self.navigationController.view.bounds.size.width, self.navigationController.view.bounds.size.height);
    [self.view addSubview:_theWorship];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:_theWorship attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.bottomLayoutGuide attribute:NSLayoutAttributeTop multiplier:1.0 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:_theWorship attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.topLayoutGuide attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:_theWorship attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0]];
    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:_theWorship attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:0]];
}

Answer 1

摆脱 addConstraint 并改为调用 isActive = true。请参阅文档:

When developing for iOS 8.0 or later, set the constraint’s active property to true instead of calling the addConstraint(_:) method directly. The isActive property automatically adds and removes the constraint from the correct view.

或者使用 NSLayoutAnchor ;它不像 NSLayoutConstraint 那样冗长。我只在循环中或当我无法用 NSLayoutAnchor 表达约束时(即居中乘法)使用 NSLayoutConstraint。