Question

我有一个依赖于iAdBanner的UIImageView位置。我收到错误：

"<NSLayoutConstraint:0x17409eb40 UIImageView:0x1741e9200.bottom == UIView:0x17418d270.bottom - 100>",
"<NSLayoutConstraint:0x174281e00 UIImageView:0x1741e9200.bottom == UIView:0x17418d270.bottom - 50>"

关于导致这种情况的任何想法？下面是设置uiimageview的代码，根据iAd是否加载，设置了它的高度。

    UIImageView *imgView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"sunshine.png"]];
    CGRect frame = imgView.frame;
    frame.size.width = 180;
    frame.size.height = 30;
    imgView.frame = frame;
    imgView.translatesAutoresizingMaskIntoConstraints = NO;

    [imgView setContentMode:UIViewContentModeScaleAspectFit];
    [imgView sizeToFit];
    [self.view addSubview:imgView];

    [self.view addConstraint:[NSLayoutConstraint
                              constraintWithItem:imgView
                              attribute:NSLayoutAttributeTrailing
                              relatedBy:NSLayoutRelationEqual
                              toItem:self.view
                              attribute:NSLayoutAttributeTrailing
                              multiplier:1.0
                              constant:6.0]];
    _imgView = imgView;

}

-(void)bannerViewDidLoadAd:(ADBannerView *)banner {
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1];
    [banner setAlpha:1];
    [UIView commitAnimations];

        [self.view addConstraint:[NSLayoutConstraint
                                  constraintWithItem:_imgView
                                  attribute:NSLayoutAttributeBottom
                                  relatedBy:NSLayoutRelationEqual
                                  toItem:self.view
                                  attribute:NSLayoutAttributeBottom
                                  multiplier:1.0
                                  constant:-100.0]];

}

-(void)bannerView:(ADBannerView *)banner didFailToReceiveAdWithError:(NSError *)error {
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1];
    [banner setAlpha:0];
    [UIView commitAnimations];

        [self.view addConstraint:[NSLayoutConstraint
                                  constraintWithItem:_imgView
                                  attribute:NSLayoutAttributeBottom
                                  relatedBy:NSLayoutRelationEqual
                                  toItem:self.view
                                  attribute:NSLayoutAttributeBottom
                                  multiplier:1.0
                                  constant:-50.0]];
}

Answer 1

据我所知，你在约束之间存在冲突，你应该删除两个约束中的一个。

Answer 2

问题是您要添加2次底部约束，一次在-(void)bannerViewDidLoadAd:(ADBannerView *)banner中，一次在(void)bannerView:(ADBannerView *)banner didFailToReceiveAdWithError:(NSError *)error方法中。约束具有不同的常量值（-100和-50），因此它们会崩溃。

这样做的正确方法是只添加一次约束，然后在2种方法中添加约束值。

这样的事情：

在第一个添加尾随约束的方法中，还要添加一个底部约束并保留对它的引用：

self.bottomOffsetConstraint = [NSLayoutConstraint
                                  constraintWithItem:_imgView
                                  attribute:NSLayoutAttributeBottom
                                  relatedBy:NSLayoutRelationEqual
                                  toItem:self.view
                                  attribute:NSLayoutAttributeBottom
                                  multiplier:1.0
                                  constant:-100.0];
[self.view addConstraint:self.bottomOffsetConstraint];

然后在2种方法中更改常量：

-(void)bannerViewDidLoadAd:(ADBannerView *)banner {
    [self.bottomOffsetConstraint setConstant:-50];
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1];
    [banner setAlpha:1];
    // You need to call this in the animation block to trigger the constraints update
    [self.view layoutIfNeeded]; 
    [UIView commitAnimations];
}

-(void)bannerView:(ADBannerView *)banner didFailToReceiveAdWithError:(NSError *)error {

    [self.bottomOffsetConstraint setConstant:-50];
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:1];
    [banner setAlpha:0];
    [self.view layoutIfNeeded];
    [UIView commitAnimations];
}

这将修复崩溃约束并为布局更改设置动画。

让我知道它是怎么回事！

以编程方式设置动态uiimageview时LayoutConstraint错误

2 个答案: