Autolayout layoutIfNeeded正在打破限制

Question

我在xib文件中創建以下視圖。 有兩個約束，我想一次一個，所以我激活一個並停用其他約束。

其中一個約束是View（頂層視圖） view.bottom == inputView.bottom 。 當文本視圖中的用戶輸入正確時，將啟用此約束。 如果用戶輸入了一些特殊字符，則會顯示錯誤消息並禁用此約束，並激活另一個約束，即view.bottom == errorLabel.bottom 。 最初這兩個約束都存在於xib文件中，但view.bottom == errorLabel.bottom設置為750優先級， view.bottom == input View.bottom設置為所需的優先級1000 。 這是為了避免沖突的約束。

現在，當用戶輸入一些輸入時，我會做以下

[NSLayoutConstraint deactivateConstraints:@[self.inputViewConstraint, self.inputViewWithErrorConstraint]];

        self.inputViewConstraint.active = (result == NBValidationResultOK);
        self.inputViewWithErrorConstraint.active = !self.inputViewConstraint.active;

        [UIView animateWithDuration:0.1 animations:^{
            [self layoutIfNeeded];
        }];


inputViewConstraint -----> view.bottom == InputView.bottom
inputViewWithErrorConstraint -----> view.bottom == errorLabel.bottom

當我執行上面的代碼調試器給我打破約束警告。

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.
2016-08-09 17:11:45.181 NB[17707:1811620] 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:0x7faf12ac8850 h=-&- v=-&- UIView:0x7faf12ac41f0.width == NBSendMoneyTextInputView:0x7faf128c8ab0.width>",
    "<NSLayoutConstraint:0x7faf12a74020 H:|-(16)-[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a4a950 UITextView:0x7faf140b7400.leading == NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel'.leading>",
    "<NSLayoutConstraint:0x7faf12a76630 H:[UITextView:0x7faf140b7400]-(16)-|   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a2ae80 H:[UIView:0x7faf12ac31e0]-(0)-|   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12a2aed0 H:|-(0)-[UIView:0x7faf12ac31e0]   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12ac5ac0 '_UITemporaryLayoutWidth' H:[NBSendMoneyTextInputView:0x7faf128c8ab0(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7faf12a4a950 UITextView:0x7faf140b7400.leading == NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel'.leading>

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.
2016-08-09 17:11:45.182 NB[17707:1811620] 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:0x7faf12ac88f0 h=-&- v=-&- UIView:0x7faf12ac41f0.height == NBSendMoneyTextInputView:0x7faf128c8ab0.height>",
    "<NSLayoutConstraint:0x7faf12aa8b20 V:[NBUISeparatorView:0x7faf12ac3990(2)]>",
    "<NSLayoutConstraint:0x7faf12a64b10 V:|-(18)-[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a368b0 V:[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']-(4)-[UITextView:0x7faf140b7400]>",
    "<NSLayoutConstraint:0x7faf12a41f60 V:[UITextView:0x7faf140b7400]-(2)-[NBUISeparatorView:0x7faf12ac3990]>",
    "<NSLayoutConstraint:0x7faf12a3e240 V:[NBUISeparatorView:0x7faf12ac3990]-(0)-|   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a211e0 V:|-(0)-[UIView:0x7faf12ac31e0]   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12a9ba30 V:[UIView:0x7faf12ac31e0]-(0)-|   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12ac5bf0 '_UITemporaryLayoutHeight' V:[NBSendMoneyTextInputView:0x7faf128c8ab0(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7faf12aa8b20 V:[NBUISeparatorView:0x7faf12ac3990(2)]>

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.
2016-08-09 17:11:45.196 NB[17707:1811620] 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:0x7faf12ac88f0 h=-&- v=-&- UIView:0x7faf12ac41f0.height == NBSendMoneyTextInputView:0x7faf128c8ab0.height>",
    "<NSLayoutConstraint:0x7faf12a64b10 V:|-(18)-[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a368b0 V:[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']-(4)-[UITextView:0x7faf140b7400]>",
    "<NSLayoutConstraint:0x7faf12a41f60 V:[UITextView:0x7faf140b7400]-(2)-[NBUISeparatorView:0x7faf12ac3990]>",
    "<NSLayoutConstraint:0x7faf12a3e240 V:[NBUISeparatorView:0x7faf12ac3990]-(0)-|   (Names: '|':UIView:0x7faf12ac31e0 )>",
    "<NSLayoutConstraint:0x7faf12a211e0 V:|-(0)-[UIView:0x7faf12ac31e0]   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12a9ba30 V:[UIView:0x7faf12ac31e0]-(0)-|   (Names: '|':UIView:0x7faf12ac41f0 )>",
    "<NSLayoutConstraint:0x7faf12ac5bf0 '_UITemporaryLayoutHeight' V:[NBSendMoneyTextInputView:0x7faf128c8ab0(0)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7faf12a368b0 V:[NBUISecondaryLabel:0x7faf12ac3560'SecondaryLabel']-(4)-[UITextView:0x7faf140b7400]>

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.

請注意，只有在調用layoutIfNeeded()方法時才會出現這些警告。

在我的公開中，沒有相互矛盾的約束。 但如果有人可以幫助我，那將是非常高興的。

Answer 1

作為建議：

您可以將其中一個約束更改為低優先級，

其中約束活動狀態之前發生了變化：

在您的情況下，低優先級約束應該是self.inputViewConstraint或self.inputViewWithErrorConstraint （不是兩者）。

Answer 2

在打開某些約束之前，必須將活動標志設置為false。 例：

self.inputViewConstraint.active = false
self.inputViewWithErrorConstraint.active = false
self.inputViewConstraint.active = result == NBValidationResultOK
self.inputViewWithErrorConstraint.active = !self.inputViewConstraint.active

如果您同時打開兩個約束，您將收到警告。