Basic UIAlertController Unable to satisfy constraints

问题

 UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title
                                                                         message:message
                                                                  preferredStyle:UIAlertControllerStyleAlert];

[alertController show];

This code is causing the following error:

...[LayoutConstraints] 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) 
(
"<NSAutoresizingMaskLayoutConstraint:0x7af32260 h=-&- v=-&- UITransitionView:0x7ae60c70.height == UIWindow:0x7aebc600.height   (active)>",
"<NSAutoresizingMaskLayoutConstraint:0x7af9b6f0 h=--- v=--- UIWindow:0x7aebc600.height == 0   (active)>",
"<NSLayoutConstraint:0x79f1f050 UIView:0x7ae6ec40.height >= 44   (active)>",
"<NSLayoutConstraint:0x79f1d6a0 _UIAlertControllerView:0x7a26ce00'Error'.height == UIView:0x7ae6ec40.height   (active)>",
"<NSLayoutConstraint:0x7aafb360 _UIAlertControllerView:0x7a26ce00'Error'.centerY == UITransitionView:0x7ae60c70.centerY   (active)>",
"<NSLayoutConstraint:0x7afb81e0 V:|-(>=0)-[_UIAlertControllerView:0x7a26ce00'Error']   (active, names: '|':UITransitionView:0x7ae60c70 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x79f1f050 UIView:0x7ae6ec40.height >= 44   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to     catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView  listed in <UIKit/UIView.h> may also be helpful.

Note: In the wider context of what my app is doing, I have no choice but to use [alertController show]

回答1:

You have UIWindow:0x7aebc600.height == 0. I'm guessing that your issue.

Obviously your window height shouldn't be set to 0, otherwise whatever that you add to it won't have enough height.

Additionally you can find a very good debugging tutorial from here. On the page search for "Will attempt to recover by breaking constraint"

来源：https://stackoverflow.com/questions/44425217/basic-uialertcontroller-unable-to-satisfy-constraints

标签

objective-c

autolayout

uialertcontroller