UIAlertController 无法满足约束

Question

我正在用UIAlertController 转换我所有的UIActionSheet 和UIAlertView。

我的问题是当我尝试呈现样式 ActionSheet 的UIAlertController 时。 这是我的代码：

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Title"
                                                               message:@"My message"
                                                        preferredStyle:UIAlertControllerStyleActionSheet];

UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil];
[alert addAction:cancelAction];

UIAlertAction *OKAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:nil];
[alert addAction:OKAction];

UIAlertAction *destroyAction = [UIAlertAction actionWithTitle:@"Destroy" style:UIAlertActionStyleDestructive handler:nil];
[alert addAction:destroyAction];

UIPopoverPresentationController *popPresenter = [alert popoverPresentationController];
popPresenter.sourceView = self.view;
popPresenter.sourceRect = self.view.bounds;

[self presentViewController:alert animated:YES completion:nil];

这是错误：

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you 
don't want. Try this: 
(1) look at each constraint and try to figure out which you don't expect; 
(2) find the code that added the unwanted constraint or constraints and fix it. 
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property 
translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x7c00ab40 H:[UIView:0x7c0764c0(304)]>",
    "<NSLayoutConstraint:0x7b6c7f80 _UIAlertControllerView:0x7b6c2e50'title'.width >= UIView:0x7b6c3230.width>",
    "<NSLayoutConstraint:0x7ccdfe40 _UIAlertControllerView:0x7b6c2e50'title'.width == UIView:0x7b6efbe0.width>",
    "<NSAutoresizingMaskLayoutConstraint:0x7c33b9d0 h=--& v=--& H:[UIView:0x7c1094e0(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7c00ab40 H:[UIView:0x7c0764c0(304)]>

谢谢大家。

Answer 1

我在提交UIAlertController 样式的 ActionSheet 时也遇到了类似的问题。

另一个可能的原因是错误地设置了UIPopoverPresentationController 的permittedArrowDirections。就我而言，弹出框的 sourceView 位于顶部，但我已将 permittedArrowDirections 设置为 UIPopoverArrowDirectionDown，这会导致“无法同时满足约束”错误。设置为UIPopoverArrowDirectionUp后错误消失了。

Answer 2

我遇到了同样的问题，因为我最初不明白sourceView 和sourceRect 必须引用与操作表相关的按钮/视图。这样弹出框就会出现在它旁边。如果改为使用整个视图，则弹出框将出现在屏幕之外，从而产生约束错误。

Answer 3

我收到此错误是因为我专注于 UITextField。首先UITextField好像有点问题，所以the code below from this SO post帮我解决了，

extension UIView
{
    func fixInputAssistant()
    {
        for subview in self.subviews
        {
            if type(of: subview) is UITextField.Type
            {
                let item = (subview as! UITextField).inputAssistantItem
                item.leadingBarButtonGroups = []
                item.trailingBarButtonGroups = []
            }
            else if subview.subviews.count > 0
            {
                subview.fixInputAssistant()
            }
        }
    }
}

但是在验证我的UITextField 时，我的UIAlertController 会引发您提到的约束冲突。为了解决这个问题，我需要在显示我的 UIAlertController 之前失去焦点，因此

firstName.resignFirstResponder()
surname.resignFirstResponder()
emailAddress.resignFirstResponder()
... etc...

请注意确定这是否与您的特定场景相关，但请注意它可能与 UITextField 焦点有关。

Answer 4

我自己找到了解决方案：

这来自以下几行：

popPresenter.sourceView = self.view;
popPresenter.sourceRect = self.view.bounds;

我必须设置 sourceView 或 sourceRect 但不能同时设置。